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The blockdev book basically contains user-faced documentation.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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Rename the block documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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Rename the blockdev documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.
The drbd sub-directory contains some graphs and data flows.
Add those too to the documentation.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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This patch includes some fixes and cleanup for idle-page writeback.
1. writeback_limit interface
Now writeback_limit interface is rather conusing. For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment. IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.
To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable
* before:
while true :
# to re-enable writeback limit once previous one is used up
echo 0 > /sys/block/zram0/writeback_limit
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget
* new
# To enable writeback limit, from the beginning, admin should
# enable it.
echo $((200<<20)) > /sys/block/zram0/writeback_limit
echo 1 > /sys/block/zram/0/writeback_limit_enable
while true :
echo $((200<<20)) > /sys/block/zram0/writeback_limit
..
.. # used up the writeback limit budget
It's much strightforward.
2. fix condition check idle/huge writeback mode check
The mode in writeback_store is not bit opeartion any more so no need to
use bit operations. Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.
3. clean up idle_store
No need to use goto.
[minchan@kernel.org: missed spin_lock_init]
Link: http://lkml.kernel.org/r/20190103001601.GA255139@google.com
Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Suggested-by: John Dias <joaodias@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: John Dias <joaodias@google.com>
Cc: Srinivas Paladugu <srnvs@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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If there are lots of write IO with flash device, it could have a
wearout problem of storage. To overcome the problem, admin needs
to design write limitation to guarantee flash health
for entire product life.
This patch creates a new knob "writeback_limit" for zram.
writeback_limit's default value is 0 so that it doesn't limit
any writeback. If admin want to measure writeback count in a
certain period, he could know it via /sys/block/zram0/bd_stat's
3rd column.
If admin want to limit writeback as per-day 400M, he could do it
like below.
MB_SHIFT=20
4K_SHIFT=12
echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
/sys/block/zram0/writeback_limit.
If admin want to allow further write again, he could do it like below
echo 0 > /sys/block/zram0/writeback_limit
If admin want to see remaining writeback budget,
cat /sys/block/zram0/writeback_limit
The writeback_limit count will reset whenever you reset zram (e.g., system
reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of writeback
happened until you reset the zram to allocate extra writeback budget in
next setting is user's job.
[minchan@kernel.org: v4]
Link: http://lkml.kernel.org/r/20181203024045.153534-8-minchan@kernel.org
Link: http://lkml.kernel.org/r/20181127055429.251614-8-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Joey Pabalinas <joeypabalinas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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bd_stat represents things that happened in the backing device. Currently
it supports bd_counts, bd_reads and bd_writes which are helpful to
understand wearout of flash and memory saving.
[minchan@kernel.org: v4]
Link: http://lkml.kernel.org/r/20181203024045.153534-7-minchan@kernel.org
Link: http://lkml.kernel.org/r/20181127055429.251614-7-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Joey Pabalinas <joeypabalinas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Add a new feature "zram idle/huge page writeback". In the zram-swap use
case, zram usually has many idle/huge swap pages. It's pointless to keep
them in memory (ie, zram).
To solve this problem, this feature introduces idle/huge page writeback to
the backing device so the goal is to save more memory space on embedded
systems.
Normal sequence to use idle/huge page writeback feature is as follows,
while (1) {
# mark allocated zram slot to idle
echo all > /sys/block/zram0/idle
# leave system working for several hours
# Unless there is no access for some blocks on zram,
# they are still IDLE marked pages.
echo "idle" > /sys/block/zram0/writeback
or/and
echo "huge" > /sys/block/zram0/writeback
# write the IDLE or/and huge marked slot into backing device
# and free the memory.
}
Per the discussion at
https://lore.kernel.org/lkml/20181122065926.GG3441@jagdpanzerIV/T/#u,
This patch removes direct incommpressibe page writeback feature
(d2afd25114f4 ("zram: write incompressible pages to backing device")).
Below concerns from Sergey:
== &< ==
"IDLE writeback" is superior to "incompressible writeback".
"incompressible writeback" is completely unpredictable and uncontrollable;
it depens on data patterns and compression algorithms. While "IDLE
writeback" is predictable.
I even suspect, that, *ideally*, we can remove "incompressible writeback".
"IDLE pages" is a super set which also includes "incompressible" pages.
So, technically, we still can do "incompressible writeback" from "IDLE
writeback" path; but a much more reasonable one, based on a page idling
period.
I understand that you want to keep "direct incompressible writeback"
around. ZRAM is especially popular on devices which do suffer from flash
wearout, so I can see "incompressible writeback" path becoming a dead
code, long term.
== &< ==
Below concerns from Minchan:
== &< ==
My concern is if we enable CONFIG_ZRAM_WRITEBACK in this implementation,
both hugepage/idlepage writeck will turn on. However someuser want to
enable only idlepage writeback so we need to introduce turn on/off knob
for hugepage or new CONFIG_ZRAM_IDLEPAGE_WRITEBACK for those usecase. I
don't want to make it complicated *if possible*.
Long term, I imagine we need to make VM aware of new swap hierarchy a
little bit different with as-is. For example, first high priority swap
can return -EIO or -ENOCOMP, swap try to fallback to next lower priority
swap device. With that, hugepage writeback will work tranparently.
So we could regard it as regression because incompressible pages doesn't
go to backing storage automatically. Instead, user should do it via "echo
huge" > /sys/block/zram/writeback" manually.
== &< ==
Link: http://lkml.kernel.org/r/20181127055429.251614-6-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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To support idle page writeback with upcoming patches, this patch
introduces a new ZRAM_IDLE flag.
Userspace can mark zram slots as "idle" via
"echo all > /sys/block/zramX/idle"
which marks every allocated zram slot as ZRAM_IDLE.
User could see it by /sys/kernel/debug/zram/zram0/block_state.
300 75.033841 ...i
301 63.806904 s..i
302 63.806919 ..hi
Once there is IO for the slot, the mark will be disappeared.
300 75.033841 ...
301 63.806904 s..i
302 63.806919 ..hi
Therefore, 300th block is idle zpage. With this feature,
user can how many zram has idle pages which are waste of memory.
Link: http://lkml.kernel.org/r/20181127055429.251614-5-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Pull documentation updates from Jonathan Corbet:
"This is a fairly typical cycle for documentation. There's some welcome
readability improvements for the formatted output, some LICENSES
updates including the addition of the ISC license, the removal of the
unloved and unmaintained 00-INDEX files, the deprecated APIs document
from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
fixes and corrections"
* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
docs: Fix typos in histogram.rst
docs: Introduce deprecated APIs list
kernel-doc: fix declaration type determination
doc: fix a typo in adding-syscalls.rst
docs/admin-guide: memory-hotplug: remove table of contents
doc: printk-formats: Remove bogus kobject references for device nodes
Documentation: preempt-locking: Use better example
dm flakey: Document "error_writes" feature
docs/completion.txt: Fix a couple of punctuation nits
LICENSES: Add ISC license text
LICENSES: Add note to CDDL-1.0 license that it should not be used
docs/core-api: memory-hotplug: add some details about locking internals
docs/core-api: rename memory-hotplug-notifier to memory-hotplug
docs: improve readability for people with poorer eyesight
yama: clarify ptrace_scope=2 in Yama documentation
docs/vm: split memory hotplug notifier description to Documentation/core-api
docs: move memory hotplug description into admin-guide/mm
doc: Fix acronym "FEKEK" in ecryptfs
docs: fix some broken documentation references
iommu: Fix passthrough option documentation
...
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This is a respin with a wider audience (all that get_maintainer returned)
and I know this spams a *lot* of people. Not sure what would be the correct
way, so my apologies for ruining your inbox.
The 00-INDEX files are supposed to give a summary of all files present
in a directory, but these files are horribly out of date and their
usefulness is brought into question. Often a simple "ls" would reveal
the same information as the filenames are generally quite descriptive as
a short introduction to what the file covers (it should not surprise
anyone what Documentation/sched/sched-design-CFS.txt covers)
A few years back it was mentioned that these files were no longer really
needed, and they have since then grown further out of date, so perhaps
it is time to just throw them out.
A short status yields the following _outdated_ 00-INDEX files, first
counter is files listed in 00-INDEX but missing in the directory, last
is files present but not listed in 00-INDEX.
List of outdated 00-INDEX:
Documentation: (4/10)
Documentation/sysctl: (0/1)
Documentation/timers: (1/0)
Documentation/blockdev: (3/1)
Documentation/w1/slaves: (0/1)
Documentation/locking: (0/1)
Documentation/devicetree: (0/5)
Documentation/power: (1/1)
Documentation/powerpc: (0/5)
Documentation/arm: (1/0)
Documentation/x86: (0/9)
Documentation/x86/x86_64: (1/1)
Documentation/scsi: (4/4)
Documentation/filesystems: (2/9)
Documentation/filesystems/nfs: (0/2)
Documentation/cgroup-v1: (0/2)
Documentation/kbuild: (0/4)
Documentation/spi: (1/0)
Documentation/virtual/kvm: (1/0)
Documentation/scheduler: (0/2)
Documentation/fb: (0/1)
Documentation/block: (0/1)
Documentation/networking: (6/37)
Documentation/vm: (1/3)
Then there are 364 subdirectories in Documentation/ with several files that
are missing 00-INDEX alltogether (and another 120 with a single file and no
00-INDEX).
I don't really have an opinion to whether or not we /should/ have 00-INDEX,
but the above 00-INDEX should either be removed or be kept up to date. If
we should keep the files, I can try to keep them updated, but I rather not
if we just want to delete them anyway.
As a starting point, remove all index-files and references to 00-INDEX and
see where the discussion is going.
Signed-off-by: Henrik Austad <henrik@austad.us>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Just-do-it-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: [Almost everybody else]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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The DAC960 driver has been obsoleted by the myrb/myrs drivers,
so it can be dropped.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Some time ago REQ_DISCARD was renamed into REQ_OP_DISCARD. Some comments
and documentation files were not updated however. Update these comments
and documentation files. See also commit 4e1b2d52a80d ("block, fs,
drivers: remove REQ_OP compat defs and related code").
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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zRam as swap is useful for small memory device. However, swap means
those pages on zram are mostly cold pages due to VM's LRU algorithm.
Especially, once init data for application are touched for launching,
they tend to be not accessed any more and finally swapped out. zRAM can
store such cold pages as compressed form but it's pointless to keep in
memory. Better idea is app developers free them directly rather than
remaining them on heap.
This patch tell us last access time of each block of zram via "cat
/sys/kernel/debug/zram/zram0/block_state".
The output is as follows,
300 75.033841 .wh
301 63.806904 s..
302 63.806919 ..h
First column is zram's block index and 3rh one represents symbol (s:
same page w: written page to backing store h: huge page) of the block
state. Second column represents usec time unit of the block was last
accessed. So above example means the 300th block is accessed at
75.033851 second and it was huge so it was written to the backing store.
Admin can leverage this information to catch cold|incompressible pages
of process with *pagemap* once part of heaps are swapped out.
I used the feature a few years ago to find memory hoggers in userspace
to notify them what memory they have wasted without touch for a long
time. With it, they could reduce unnecessary memory space. However, at
that time, I hacked up zram for the feature but now I need the feature
again so I decided it would be better to upstream rather than keeping it
alone. I hope I submit the userspace tool to use the feature soon.
[akpm@linux-foundation.org: fix i386 printk warning]
[minchan@kernel.org: use ktime_get_boottime() instead of sched_clock()]
Link: http://lkml.kernel.org/r/20180420063525.GA253739@rodete-desktop-imager.corp.google.com
[akpm@linux-foundation.org: documentation tweak]
[akpm@linux-foundation.org: fix i386 printk warning]
[minchan@kernel.org: fix compile warning]
Link: http://lkml.kernel.org/r/20180508104849.GA8209@rodete-desktop-imager.corp.google.com
[rdunlap@infradead.org: fix printk formats]
Link: http://lkml.kernel.org/r/3652ccb1-96ef-0b0b-05d1-f661d7733dcc@infradead.org
Link: http://lkml.kernel.org/r/20180416090946.63057-5-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Mark incompressible pages so that we could investigate who is the owner
of the incompressible pages once the page is swapped out via using
upcoming zram memory tracker feature.
With it, we could prevent such pages to be swapped out by using mlock.
Otherwise we might remove them.
This patch exposes new stat for huge pages via mm_stat.
Link: http://lkml.kernel.org/r/20180416090946.63057-3-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Pull SCSI updates from James Bottomley:
"This is mostly updates of the usual suspects: lpfc, qla2xxx, hisi_sas,
megaraid_sas, zfcp and a host of minor updates.
The major driver change here is the elimination of the block based
cciss driver in favour of the SCSI based hpsa driver (which now drives
all the legacy cases cciss used to be required for). Plus a reset
handler clean up and the redo of the SAS SMP handler to use bsg lib"
* tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi: (279 commits)
scsi: scsi-mq: Always unprepare before requeuing a request
scsi: Show .retries and .jiffies_at_alloc in debugfs
scsi: Improve requeuing behavior
scsi: Call scsi_initialize_rq() for filesystem requests
scsi: qla2xxx: Reset the logo flag, after target re-login.
scsi: qla2xxx: Fix slow mem alloc behind lock
scsi: qla2xxx: Clear fc4f_nvme flag
scsi: qla2xxx: add missing includes for qla_isr
scsi: qla2xxx: Fix an integer overflow in sysfs code
scsi: aacraid: report -ENOMEM to upper layer from aac_convert_sgraw2()
scsi: aacraid: get rid of one level of indentation
scsi: aacraid: fix indentation errors
scsi: storvsc: fix memory leak on ring buffer busy
scsi: scsi_transport_sas: switch to bsg-lib for SMP passthrough
scsi: smartpqi: remove the smp_handler stub
scsi: hpsa: remove the smp_handler stub
scsi: bsg-lib: pass the release callback through bsg_setup_queue
scsi: Rework handling of scsi_device.vpd_pg8[03]
scsi: Rework the code for caching Vital Product Data (VPD)
scsi: rcu: Introduce rcu_swap_protected()
...
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The hpsa driver now has support for all boards the cciss driver
used to support, so this patch removes the cciss driver and
make hpsa an alias to cciss.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Acked-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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This patch adds document and kconfig for using of writeback feature.
Link: http://lkml.kernel.org/r/1498459987-24562-10-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This drivers was added in 2008, but as far as a I can tell we never had a
single platform that actually registered resources for the platform driver.
It's also been unmaintained for a long time and apparently has a ATA mode
that can be driven using the IDE/libata subsystem.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
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Fix typos and add the following to the scripts/spelling.txt:
followings||following
While we are here, add a missing colon in the boilerplate in DT binding
documents. The "you SoC" in allwinner,sunxi-pinctrl.txt was fixed as
well.
I reworded "as the followings:" to "as follows:" for
drivers/usb/gadget/udc/renesas_usb3.c.
Link: http://lkml.kernel.org/r/1481573103-11329-32-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The idea is that without doing more calculations we extend zero pages to
same element pages for zram. zero page is special case of same element
page with zero element.
1. the test is done under android 7.0
2. startup too many applications circularly
3. sample the zero pages, same pages (none-zero element)
and total pages in function page_zero_filled
the result is listed as below:
ZERO SAME TOTAL
36214 17842 598196
ZERO/TOTAL SAME/TOTAL (ZERO+SAME)/TOTAL ZERO/SAME
AVERAGE 0.060631909 0.024990816 0.085622726 2.663825038
STDEV 0.00674612 0.005887625 0.009707034 2.115881328
MAX 0.069698422 0.030046087 0.094975336 7.56043956
MIN 0.03959586 0.007332205 0.056055193 1.928985507
from the above data, the benefit is about 2.5% and up to 3% of total
swapout pages.
The defect of the patch is that when we recovery a page from non-zero
element the operations are low efficient for partial read.
This patch extends zero_page to same_page so if there is any user to
have monitored zero_pages, he will be surprised if the number is
increased but it's not harmful, I believe.
[minchan@kernel.org: do not free same element pages in zram_meta_free]
Link: http://lkml.kernel.org/r/20170207065741.GA2567@bbox
Link: http://lkml.kernel.org/r/1483692145-75357-1-git-send-email-zhouxianrong@huawei.com
Link: http://lkml.kernel.org/r/1486307804-27903-1-git-send-email-minchan@kernel.org
Signed-off-by: zhouxianrong <zhouxianrong@huawei.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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We had a deprecated_attr_warn() warning for 2 years and now the time has
come and we finally can do the cleanup.
The plan was as follows:
: per-stat sysfs attributes are considered to be deprecated.
: The basic strategy is:
: -- the existing RW nodes will be downgraded to WO nodes (in linux 4.11)
: -- deprecated RO sysfs nodes will eventually be removed (in linux 4.11)
:
: The list of deprecated attributes can be found here:
: Documentation/ABI/obsolete/sysfs-block-zram
:
: Basically, every attribute that has its own read accessible sysfs
: node (e.g. num_reads) *AND* is accessible via one of the stat files
: (zram<id>/stat or zram<id>/io_stat or zram<id>/mm_stat) is considered
: to be deprecated.
The patch also removes `obsolete/sysfs-block-zram', clean ups
`testing/sysfs-block-zram' and tweaks zram.txt files.
Link: http://lkml.kernel.org/r/20170118035838.11090-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The previous patch renamed several files that are cross-referenced
along the Kernel documentation. Adjust the links to point to
the right places.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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This patch fix a spelling typo in cciss.txt
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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zram documentation is a mix of different styles: spaces, tabs, tabs +
spaces, etc. Clean it up.
Link: http://lkml.kernel.org/r/20160531122017.2878-6-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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There is no way to get a string with all the crypto comp algorithms
supported by the crypto comp engine, so we need to maintain our own
backends list. At the same time we additionally need to use
crypto_has_comp() to make sure that the user has requested a compression
algorithm that is recognized by the crypto comp engine. Relying on
/proc/crypto is not an options here, because it does not show
not-yet-inserted compression modules.
Example:
modprobe zram
cat /proc/crypto | grep -i lz4
modprobe lz4
cat /proc/crypto | grep -i lz4
name : lz4
driver : lz4-generic
module : lz4
So the user can't tell exactly if the lz4 is really supported from
/proc/crypto output, unless someone or something has loaded it.
This patch also adds crypto_has_comp() to zcomp_available_show(). We
store all the compression algorithms names in zcomp's `backends' array,
regardless the CONFIG_CRYPTO_FOO configuration, but show only those that
are also supported by crypto engine. This helps user to know the exact
list of compression algorithms that can be used.
Example:
module lz4 is not loaded yet, but is supported by the crypto
engine. /proc/crypto has no information on this module, while
zram's `comp_algorithm' lists it:
cat /proc/crypto | grep -i lz4
cat /sys/block/zram0/comp_algorithm
[lzo] lz4 deflate lz4hc 842
We still use the `backends' array to determine if the requested
compression backend is known to crypto api. This array, however, may not
contain some entries, therefore as the last step we call crypto_has_comp()
function which attempts to insmod the requested compression algorithm to
determine if crypto api supports it. The advantage of this method is that
now we permit the usage of out-of-tree crypto compression modules
(implementing S/W or H/W compression).
[sergey.senozhatsky@gmail.com: zram-use-crypto-api-to-check-alg-availability-v3]
Link: http://lkml.kernel.org/r/20160604024902.11778-4-sergey.senozhatsky@gmail.com
Link: http://lkml.kernel.org/r/20160531122017.2878-5-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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debug_stat sysfs is read-only and represents various debugging data that
zram developers may need. This file is not meant to be used by anyone
else: its content is not documented and will change any time w/o any
notice. Therefore, the output of debug_stat file contains a version
string. To avoid any confusion, we will increase the version number
every time we modify the output.
At the moment this file exports only one value -- the number of
re-compressions, IOW, the number of times compression fast path has
failed. This stat is temporary any will be useful in case if any
per-cpu compression streams regressions will be reported.
Link: http://lkml.kernel.org/r/20160513230834.GB26763@bbox
Link: http://lkml.kernel.org/r/20160511134553.12655-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Remove the internal part of max_comp_streams interface, since we
switched to per-cpu streams. We will keep RW max_comp_streams attr
around, because:
a) we may (silently) switch back to idle compression streams list and
don't want to disturb user space
b) max_comp_streams attr must wait for the next 'lay off cycle'; we
give user space 2 years to adjust before we remove/downgrade the attr,
and there are already several attrs scheduled for removal in 4.11, so
it's too late for max_comp_streams.
This slightly change a user visible behaviour:
- First, reading from max_comp_stream file now will always return the
number of online CPUs.
- Second, writing to max_comp_stream will not take any effect.
Link: http://lkml.kernel.org/r/20160503165546.25201-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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We disabled the ability to enable this driver back in October of 2013,
we should be able to safely remove it at this point. The initial goal
was to remove it in 3.15, so now is the time.
Signed-off-by: Jens Axboe <axboe@fb.com>
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Several documentation changes.
First, we never mentioned any errors and never required any
error checks in documentation.
Second, mention that there is another way to configure and
manage zram devices -- zramctl, provided by util-linux.
Third, add a bit of clarification on why `mem_used_max' attr
is RW and correct some typos.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Compaction returns back to zram the number of migrated objects, which is
quite uninformative -- we have objects of different sizes so user space
cannot obtain any valuable data from that number. Change compaction to
operate in terms of pages and return back to compaction issuer the
number of pages that were freed during compaction. So from now on we
will export more meaningful value in zram<id>/mm_stat -- the number of
freed (compacted) pages.
This requires:
(a) a rename of `num_migrated' to 'pages_compacted'
(b) a internal API change -- return first_page's fullness_group from
putback_zspage(), so we know when putback_zspage() did
free_zspage(). It helps us to account compaction stats correctly.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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We currently don't support on-demand device creation. The one and only
way to have N zram devices is to specify num_devices module parameter
(default value: 1). IOW if, for some reason, at some point, user wants
to have N + 1 devies he/she must umount all the existing devices, unload
the module, load the module passing num_devices equals to N + 1. And do
this again, if needed.
This patch introduces zram control sysfs class, which has two sysfs
attrs:
- hot_add -- add a new zram device
- hot_remove -- remove a specific (device_id) zram device
hot_add sysfs attr is read-only and has only automatic device id
assignment mode (as requested by Minchan Kim). read operation performed
on this attr creates a new zram device and returns back its device_id or
error status.
Usage example:
# add a new specific zram device
cat /sys/class/zram-control/hot_add
2
# remove a specific zram device
echo 4 > /sys/class/zram-control/hot_remove
Returning zram_add() error code back to user (-ENOMEM in this case)
cat /sys/class/zram-control/hot_add
cat: /sys/class/zram-control/hot_add: Cannot allocate memory
NOTE, there might be users who already depend on the fact that at least
zram0 device gets always created by zram_init(). Preserve this behavior.
[minchan@kernel.org: use zram->claim to avoid lockdep splat]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Limiting the number of zram devices to 32 (default max_num_devices value)
is confusing, let's drop it. A user with 2TB or 4TB of RAM, for example,
can request as many devices as he can handle.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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We currently don't support zram on-demand device creation. The only way
to have N zram devices is to specify num_devices module parameter (default
value 1). That means that if, for some reason, at some point, user wants
to have N + 1 devies he/she must umount all the existing devices, unload
the module, load the module passing num_devices equals to N + 1.
This patchset introduces zram-control sysfs class, which has two sysfs
attrs:
- hot_add -- add a new zram device
- hot_remove -- remove a specific (device_id) zram device
Usage example:
# add a new specific zram device
cat /sys/class/zram-control/hot_add
1
# remove a specific zram device
echo 4 > /sys/class/zram-control/hot_remove
This patch (of 10):
Briefly describe missing `compact` sysfs entry.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Pull block driver updates from Jens Axboe:
"This is the block driver pull request for 4.1. As with the core bits,
this is a relatively slow round. This pull request contains:
- Various fixes and cleanups for NVMe, from Alexey Khoroshilov, Chong
Yuan, myself, Keith Busch, and Murali Iyer.
- Documentation and code cleanups for nbd from Markus Pargmann.
- Change of brd maintainer to me, from Ross Zwisler. At least the
email doesn't bounce anymore then.
- Two xen-blkback fixes from Tao Chen"
* 'for-4.1/drivers' of git://git.kernel.dk/linux-block: (23 commits)
NVMe: Meta data handling through submit io ioctl
NVMe: Add translation for block limits
NVMe: Remove check for null
NVMe: Fix error handling of class_create("nvme")
xen-blkback: define pr_fmt macro to avoid the duplication of DRV_PFX
xen-blkback: enlarge the array size of blkback name
nbd: Return error pointer directly
nbd: Return error code directly
nbd: Remove fixme that was already fixed
nbd: Restructure debugging prints
nbd: Fix device bytesize type
nbd: Replace kthread_create with kthread_run
nbd: Remove kernel internal header
Documentation: nbd: Add list of module parameters
Documentation: nbd: Reformat to allow more documentation
NVMe: increase depth of admin queue
nvme: Fix PRP list calculation for non-4k system page size
NVMe: Fix blk-mq hot cpu notification
NVMe: embedded iod mask cleanup
NVMe: Freeze admin queue on device failure
...
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Add a list of available module parameters as attachment to the
documentation.
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
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Reformat the existing documentation to have more structure. This allows
for more documentation seperated from the existing paragraphs.
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
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Add Documentation/ABI/obsolete/sysfs-block-zram file and list obsolete and
deprecated attributes there. The patch also adds additional information
to zram documentation and describes the basic strategy:
- the existing RW nodes will be downgraded to WO nodes (in 4.11)
- deprecated RO sysfs nodes will eventually be removed (in 4.11)
Users will be additionally notified about deprecated attr usage by
pr_warn_once() (added to every deprecated attr _show()), as suggested by
Minchan Kim.
User space is advised to use zram<id>/stat, zram<id>/io_stat and
zram<id>/mm_stat files.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Per-device `zram<id>/mm_stat' file provides mm statistics of a particular
zram device in a format similar to block layer statistics. The file
consists of a single line and represents the following stats (separated by
whitespace):
orig_data_size
compr_data_size
mem_used_total
mem_limit
mem_used_max
zero_pages
num_migrated
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Per-device `zram<id>/io_stat' file provides accumulated I/O statistics of
particular zram device in a format similar to block layer statistics. The
file consists of a single line and represents the following stats
(separated by whitespace):
failed_reads
failed_writes
invalid_io
notify_free
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Briefly describe exported device stat attrs in zram documentation. We
will eventually get rid of per-stat sysfs nodes and, thus, clean up
Documentation/ABI/testing/sysfs-block-zram file, which is the only source
of information about device sysfs nodes.
Add `num_migrated' description, since there is no independent
`num_migrated' sysfs node (and no corresponding sysfs-block-zram entry),
it will be exported via zram<id>/mm_stat file.
At this point we can provide minimal description, because sysfs-block-zram
still contains detailed information.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Normally, zram user could get maximum memory usage zram consumed via
polling mem_used_total with sysfs in userspace.
But it has a critical problem because user can miss peak memory usage
during update inverval of polling. For avoiding that, user should poll it
with shorter interval(ie, 0.0000000001s) with mlocking to avoid page fault
delay when memory pressure is heavy. It would be troublesome.
This patch adds new knob "mem_used_max" so user could see the maximum
memory usage easily via reading the knob and reset it via "echo 0 >
/sys/block/zram0/mem_used_max".
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Dan Streetman <ddstreet@ieee.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: <juno.choi@lge.com>
Cc: <seungho1.park@lge.com>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjennings@variantweb.net>
Reviewed-by: David Horner <ds2horner@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Since zram has no control feature to limit memory usage, it makes hard to
manage system memrory.
This patch adds new knob "mem_limit" via sysfs to set up the a limit so
that zram could fail allocation once it reaches the limit.
In addition, user could change the limit in runtime so that he could
manage the memory more dynamically.
Initial state is no limit so it doesn't break old behavior.
[akpm@linux-foundation.org: fix typo, per Sergey]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: <juno.choi@lge.com>
Cc: <seungho1.park@lge.com>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: David Horner <ds2horner@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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When we initialized zcomp with single, we couldn't change
max_comp_streams without zram reset but current interface doesn't show
any error to user and even it changes max_comp_streams's value without
any effect so it would make user very confusing.
This patch prevents max_comp_streams's change when zcomp was initialized
as single zcomp and emit the error to user(ex, echo).
[akpm@linux-foundation.org: don't return with the lock held, per Sergey]
[fengguang.wu@intel.com: fix coccinelle warnings]
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Add and document `comp_algorithm' device attribute. This attribute allows
to show supported compression and currently selected compression
algorithms:
cat /sys/block/zram0/comp_algorithm
[lzo] lz4
and change selected compression algorithm:
echo lzo > /sys/block/zram0/comp_algorithm
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Existing zram (zcomp) implementation has only one compression stream
(buffer and algorithm private part), so in order to prevent data
corruption only one write (compress operation) can use this compression
stream, forcing all concurrent write operations to wait for stream lock
to be released. This patch changes zcomp to keep a compression streams
list of user-defined size (via sysfs device attr). Each write operation
still exclusively holds compression stream, the difference is that we
can have N write operations (depending on size of streams list)
executing in parallel. See TEST section later in commit message for
performance data.
Introduce struct zcomp_strm_multi and a set of functions to manage
zcomp_strm stream access. zcomp_strm_multi has a list of idle
zcomp_strm structs, spinlock to protect idle list and wait queue, making
it possible to perform parallel compressions.
The following set of functions added:
- zcomp_strm_multi_find()/zcomp_strm_multi_release()
find and release a compression stream, implement required locking
- zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
create and destroy zcomp_strm_multi
zcomp ->strm_find() and ->strm_release() callbacks are set during
initialisation to zcomp_strm_multi_find()/zcomp_strm_multi_release()
correspondingly.
Each time zcomp issues a zcomp_strm_multi_find() call, the following set
of operations performed:
- spin lock strm_lock
- if idle list is not empty, remove zcomp_strm from idle list, spin
unlock and return zcomp stream pointer to caller
- if idle list is empty, current adds itself to wait queue. it will be
awaken by zcomp_strm_multi_release() caller.
zcomp_strm_multi_release():
- spin lock strm_lock
- add zcomp stream to idle list
- spin unlock, wake up sleeper
Minchan Kim reported that spinlock-based locking scheme has demonstrated
a severe perfomance regression for single compression stream case,
comparing to mutex-based (see https://lkml.org/lkml/2014/2/18/16)
base spinlock mutex
==Initial write ==Initial write ==Initial write
records: 5 records: 5 records: 5
avg: 1642424.35 avg: 699610.40 avg: 1655583.71
std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96
max: 1690170.94 max: 1163473.45 max: 1697164.75
min: 1568669.52 min: 573429.88 min: 1553410.23
==Rewrite ==Rewrite ==Rewrite
records: 5 records: 5 records: 5
avg: 1611775.39 avg: 501406.64 avg: 1684419.11
std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42
max: 1641800.95 max: 531356.78 max: 1706445.84
min: 1593515.27 min: 488817.78 min: 1655335.73
When only one compression stream available, mutex with spin on owner
tends to perform much better than frequent wait_event()/wake_up(). This
is why single stream implemented as a special case with mutex locking.
Introduce and document zram device attribute max_comp_streams. This
attr shows and stores current zcomp's max number of zcomp streams
(max_strm). Extend zcomp's zcomp_create() with `max_strm' parameter.
`max_strm' limits the number of zcomp_strm structs in compression
backend's idle list (max_comp_streams).
max_comp_streams used during initialisation as follows:
-- passing to zcomp_create() max_strm equals to 1 will initialise zcomp
using single compression stream zcomp_strm_single (mutex-based locking).
-- passing to zcomp_create() max_strm greater than 1 will initialise zcomp
using multi compression stream zcomp_strm_multi (spinlock-based locking).
default max_comp_streams value is 1, meaning that zram with single stream
will be initialised.
Later patch will introduce configuration knob to change max_comp_streams
on already initialised and used zcomp.
TEST
iozone -t 3 -R -r 16K -s 60M -I +Z
test base 1 strm (mutex) 3 strm (spinlock)
-----------------------------------------------------------------------
Initial write 589286.78 583518.39 718011.05
Rewrite 604837.97 596776.38 1515125.72
Random write 584120.11 595714.58 1388850.25
Pwrite 535731.17 541117.38 739295.27
Fwrite 1418083.88 1478612.72 1484927.06
Usage example:
set max_comp_streams to 4
echo 4 > /sys/block/zram0/max_comp_streams
show current max_comp_streams (default value is 1).
cat /sys/block/zram0/max_comp_streams
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Document `failed_reads' and `failed_writes' device attributes.
Remove info about `discard' - there is no such zram attr.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Move zram warning about disksize and size of memory correlation to zram
documentation.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The following commits will successively transform DRBD into the structure
described here.
Signed-off-by: Andreas Gruenbacher <agruen@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
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Remove the old private compcache project address so upcoming patches
should be sent to LKML because we Linux kernel community will take care.
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Zram has lived in staging for a LONG LONG time and have been
fixed/improved by many contributors so code is clean and stable now. Of
course, there are lots of product using zram in real practice.
The major TV companys have used zram as swap since two years ago and
recently our production team released android smart phone with zram
which is used as swap, too and recently Android Kitkat start to use zram
for small memory smart phone. And there was a report Google released
their ChromeOS with zram, too and cyanogenmod have been used zram long
time ago. And I heard some disto have used zram block device for tmpfs.
In addition, I saw many report from many other peoples. For example,
Lubuntu start to use it.
The benefit of zram is very clear. With my experience, one of the
benefit was to remove jitter of video application with backgroud memory
pressure. It would be effect of efficient memory usage by compression
but more issue is whether swap is there or not in the system. Recent
mobile platforms have used JAVA so there are many anonymous pages. But
embedded system normally are reluctant to use eMMC or SDCard as swap
because there is wear-leveling and latency issues so if we do not use
swap, it means we can't reclaim anoymous pages and at last, we could
encounter OOM kill. :(
Although we have real storage as swap, it was a problem, too. Because
it sometime ends up making system very unresponsible caused by slow swap
storage performance.
Quote from Luigi on Google
"Since Chrome OS was mentioned: the main reason why we don't use swap
to a disk (rotating or SSD) is because it doesn't degrade gracefully
and leads to a bad interactive experience. Generally we prefer to
manage RAM at a higher level, by transparently killing and restarting
processes. But we noticed that zram is fast enough to be competitive
with the latter, and it lets us make more efficient use of the
available RAM. " and he announced.
http://www.spinics.net/lists/linux-mm/msg57717.html
Other uses case is to use zram for block device. Zram is block device
so anyone can format the block device and mount on it so some guys on
the internet start zram as /var/tmp.
http://forums.gentoo.org/viewtopic-t-838198-start-0.html
Let's promote zram and enhance/maintain it instead of removing.
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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