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authorMichal Hocko <mhocko@suse.com>2017-07-11 00:49:38 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-11 01:32:32 +0200
commitd09b6468824d9e41dc30708475f954e455cf7146 (patch)
tree39dcafb5160c681e432749b8dd858bd8559e3982
parentinclude/linux/backing-dev.h: simplify wb_stat_sum (diff)
downloadlinux-d09b6468824d9e41dc30708475f954e455cf7146.tar.xz
linux-d09b6468824d9e41dc30708475f954e455cf7146.zip
mm: document highmem_is_dirtyable sysctl
It seems that there are still people using 32b kernels which a lot of memory and the IO tend to suck a lot for them by default. Mostly because writers are throttled too when the lowmem is used. We have highmem_is_dirtyable to work around that issue but it seems we never bothered to document it. Let's do it now, finally. Link: http://lkml.kernel.org/r/20170626093200.18958-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Alkis Georgopoulos <alkisg@gmail.com> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--Documentation/sysctl/vm.txt20
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index b4ad97f10b8e..48244c42ff52 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -240,6 +240,26 @@ fragmentation index is <= extfrag_threshold. The default value is 500.
==============================================================
+highmem_is_dirtyable
+
+Available only for systems with CONFIG_HIGHMEM enabled (32b systems).
+
+This parameter controls whether the high memory is considered for dirty
+writers throttling. This is not the case by default which means that
+only the amount of memory directly visible/usable by the kernel can
+be dirtied. As a result, on systems with a large amount of memory and
+lowmem basically depleted writers might be throttled too early and
+streaming writes can get very slow.
+
+Changing the value to non zero would allow more memory to be dirtied
+and thus allow writers to write more data which can be flushed to the
+storage more effectively. Note this also comes with a risk of pre-mature
+OOM killer because some writers (e.g. direct block device writes) can
+only use the low memory and they can fill it up with dirty data without
+any throttling.
+
+==============================================================
+
hugepages_treat_as_movable
This parameter controls whether we can allocate hugepages from ZONE_MOVABLE