Merge branch 'linus' into core/softlockup

19 files changed, 332 insertions, 25 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index 5ac1e01bbd48..5f500977b42f 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -14,6 +14,10 @@ MAJOR:MINOR
 	non-block filesystems which provide their own BDI, such as NFS
 	and FUSE.
 
+MAJOR:MINOR-fuseblk
+
+	Value of st_dev on fuseblk filesystems.
+
 default
 
 	The default backing dev, used for non-block device backed
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
index 77c42f40be5d..2510763295d0 100644
--- a/Documentation/DocBook/kernel-locking.tmpl
+++ b/Documentation/DocBook/kernel-locking.tmpl
@@ -703,6 +703,31 @@
 </sect1>
 </chapter>
 
+<chapter id="trylock-functions">
+ <title>The trylock Functions</title>
+  <para>
+   There are functions that try to acquire a lock only once and immediately
+   return a value telling about success or failure to acquire the lock.
+   They can be used if you need no access to the data protected with the lock
+   when some other thread is holding the lock. You should acquire the lock
+   later if you then need access to the data protected with the lock.
+  </para>
+
+  <para>
+    <function>spin_trylock()</function> does not spin but returns non-zero if
+    it acquires the spinlock on the first try or 0 if not. This function can
+    be used in all contexts like <function>spin_lock</function>: you must have
+    disabled the contexts that might interrupt you and acquire the spin lock.
+  </para>
+
+  <para>
+    <function>mutex_trylock()</function> does not suspend your task
+    but returns non-zero if it could lock the mutex on the first try
+    or 0 if not. This function cannot be safely used in hardware or software
+    interrupt contexts despite not sleeping.
+  </para>
+</chapter>
+
   <chapter id="Examples">
    <title>Common Examples</title>
     <para>
diff --git a/Documentation/SubmittingPatches b/Documentation/SubmittingPatches
index 9c93a03ea33b..118ca6e9404f 100644
--- a/Documentation/SubmittingPatches
+++ b/Documentation/SubmittingPatches
@@ -327,6 +327,52 @@ Some people also put extra tags at the end.  They'll just be ignored for
 now, but you can do this to mark internal company procedures or just
 point out some special detail about the sign-off. 
 
+If you are a subsystem or branch maintainer, sometimes you need to slightly
+modify patches you receive in order to merge them, because the code is not
+exactly the same in your tree and the submitters'. If you stick strictly to
+rule (c), you should ask the submitter to rediff, but this is a totally
+counter-productive waste of time and energy. Rule (b) allows you to adjust
+the code, but then it is very impolite to change one submitter's code and
+make him endorse your bugs. To solve this problem, it is recommended that
+you add a line between the last Signed-off-by header and yours, indicating
+the nature of your changes. While there is nothing mandatory about this, it
+seems like prepending the description with your mail and/or name, all
+enclosed in square brackets, is noticeable enough to make it obvious that
+you are responsible for last-minute changes. Example :
+
+	Signed-off-by: Random J Developer <random@developer.example.org>
+	[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
+	Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
+
+This practise is particularly helpful if you maintain a stable branch and
+want at the same time to credit the author, track changes, merge the fix,
+and protect the submitter from complaints. Note that under no circumstances
+can you change the author's identity (the From header), as it is the one
+which appears in the changelog.
+
+Special note to back-porters: It seems to be a common and useful practise
+to insert an indication of the origin of a patch at the top of the commit
+message (just after the subject line) to facilitate tracking. For instance,
+here's what we see in 2.6-stable :
+
+    Date:   Tue May 13 19:10:30 2008 +0000
+
+        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
+
+        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
+
+And here's what appears in 2.4 :
+
+    Date:   Tue May 13 22:12:27 2008 +0200
+
+        wireless, airo: waitbusy() won't delay
+
+        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
+
+Whatever the format, this information provides a valuable help to people
+tracking your trees, and to people trying to trouble-shoot bugs in your
+tree.
+
 
 13) When to use Acked-by: and Cc:
 
diff --git a/Documentation/cciss.txt b/Documentation/cciss.txt
index e65736c6b8bc..63e59b8847c5 100644
--- a/Documentation/cciss.txt
+++ b/Documentation/cciss.txt
@@ -21,6 +21,11 @@ This driver is known to work with the following cards:
 	* SA E200
 	* SA E200i
 	* SA E500
+	* SA P212
+	* SA P410
+	* SA P410i
+	* SA P411
+	* SA P812
 
 Detecting drive failures:
 -------------------------
diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index 6a9c55bd556b..dcec0564d040 100644
--- a/Documentation/cpu-freq/governors.txt
+++ b/Documentation/cpu-freq/governors.txt
@@ -129,14 +129,6 @@ to its default value of '80' it means that between the checking
 intervals the CPU needs to be on average more than 80% in use to then
 decide that the CPU frequency needs to be increased.  
 
-sampling_down_factor: this parameter controls the rate that the CPU
-makes a decision on when to decrease the frequency.  When set to its
-default value of '5' it means that at 1/5 the sampling_rate the kernel
-makes a decision to lower the frequency.  Five "lower rate" decisions
-have to be made in a row before the CPU frequency is actually lower.
-If set to '1' then the frequency decreases as quickly as it increases,
-if set to '2' it decreases at half the rate of the increase.
-
 ignore_nice_load: this parameter takes a value of '0' or '1'. When
 set to '0' (its default), all processes are counted towards the
 'cpu utilisation' value.  When set to '1', the processes that are
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index fb7b361e6eea..d803c5c68ab5 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -199,7 +199,7 @@ using the sched_setaffinity, mbind and set_mempolicy system calls.
 The following rules apply to each cpuset:
 
  - Its CPUs and Memory Nodes must be a subset of its parents.
- - It can only be marked exclusive if its parent is.
+ - It can't be marked exclusive unless its parent is.
  - If its cpu or memory is exclusive, they may not overlap any sibling.
 
 These rules, and the natural hierarchy of cpusets, enable efficient
@@ -345,7 +345,7 @@ is modified to perform an inline check for this PF_SPREAD_PAGE task
 flag, and if set, a call to a new routine cpuset_mem_spread_node()
 returns the node to prefer for the allocation.
 
-Similarly, setting 'memory_spread_cache' turns on the flag
+Similarly, setting 'memory_spread_slab' turns on the flag
 PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
 pages from the node returned by cpuset_mem_spread_node().
 
@@ -709,7 +709,10 @@ Now you want to do something with this cpuset.
 
 In this directory you can find several files:
 # ls
-cpus  cpu_exclusive  mems  mem_exclusive mem_hardwall  tasks
+cpu_exclusive  memory_migrate      mems                      tasks
+cpus           memory_pressure     notify_on_release
+mem_exclusive  memory_spread_page  sched_load_balance
+mem_hardwall   memory_spread_slab  sched_relax_domain_level
 
 Reading them will give you information about the state of this cpuset:
 the CPUs and Memory Nodes it can use, the processes that are using
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 560f88dc7090..0c5086db8352 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -139,8 +139,16 @@ commit=nrsec	(*)	Ext4 can be told to sync all its data and metadata
 			Setting it to very large values will improve
 			performance.
 
-barrier=1		This enables/disables barriers.  barrier=0 disables
-			it, barrier=1 enables it.
+barrier=<0|1(*)>	This enables/disables the use of write barriers in
+			the jbd code.  barrier=0 disables, barrier=1 enables.
+			This also requires an IO stack which can support
+			barriers, and if jbd gets an error on a barrier
+			write, it will disable again with a warning.
+			Write barriers enforce proper on-disk ordering
+			of journal commits, making volatile disk write caches
+			safe to use, at some performance penalty.  If
+			your disks are battery-backed in one way or another,
+			disabling barriers may safely improve performance.
 
 orlov		(*)	This enables the new Orlov block allocator. It is
 			enabled by default.
diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 5daa2aaec2c5..68ef48839c04 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -36,6 +36,7 @@ files, each with their own function.
        local_cpus	   nearby CPU mask (cpumask, ro)
        resource		   PCI resource host addresses (ascii, ro)
        resource0..N	   PCI resource N, if present (binary, mmap)
+       resource0_wc..N_wc  PCI WC map resource N, if prefetchable (binary, mmap)
        rom		   PCI ROM resource, if present (binary, ro)
        subsystem_device	   PCI subsystem device (ascii, ro)
        subsystem_vendor	   PCI subsystem vendor (ascii, ro)
diff --git a/Documentation/hwmon/ibmaem b/Documentation/hwmon/ibmaem
new file mode 100644
index 000000000000..2fefaf582a43
--- /dev/null
+++ b/Documentation/hwmon/ibmaem
@@ -0,0 +1,37 @@
+Kernel driver ibmaem
+======================
+
+Supported systems:
+  * Any recent IBM System X server with Active Energy Manager support.
+    This includes the x3350, x3550, x3650, x3655, x3755, x3850 M2,
+    x3950 M2, and certain HS2x/LS2x/QS2x blades.  The IPMI host interface
+    driver ("ipmi-si") needs to be loaded for this driver to do anything.
+    Prefix: 'ibmaem'
+    Datasheet: Not available
+
+Author: Darrick J. Wong
+
+Description
+-----------
+
+This driver implements sensor reading support for the energy and power
+meters available on various IBM System X hardware through the BMC.  All
+sensor banks will be exported as platform devices; this driver can talk
+to both v1 and v2 interfaces.  This driver is completely separate from the
+older ibmpex driver.
+
+The v1 AEM interface has a simple set of features to monitor energy use.
+There is a register that displays an estimate of raw energy consumption
+since the last BMC reset, and a power sensor that returns average power
+use over a configurable interval.
+
+The v2 AEM interface is a bit more sophisticated, being able to present
+a wider range of energy and power use registers, the power cap as
+set by the AEM software, and temperature sensors.
+
+Special Features
+----------------
+
+The "power_cap" value displays the current system power cap, as set by
+the Active Energy Manager software.  Setting the power cap from the host
+is not currently supported.
diff --git a/Documentation/kernel-doc-nano-HOWTO.txt b/Documentation/kernel-doc-nano-HOWTO.txt
index 2075c0658bf5..0bd32748a467 100644
--- a/Documentation/kernel-doc-nano-HOWTO.txt
+++ b/Documentation/kernel-doc-nano-HOWTO.txt
@@ -1,6 +1,105 @@
 kernel-doc nano-HOWTO
 =====================
 
+How to format kernel-doc comments
+---------------------------------
+
+In order to provide embedded, 'C' friendly, easy to maintain,
+but consistent and extractable documentation of the functions and
+data structures in the Linux kernel, the Linux kernel has adopted
+a consistent style for documenting functions and their parameters,
+and structures and their members.
+
+The format for this documentation is called the kernel-doc format.
+It is documented in this Documentation/kernel-doc-nano-HOWTO.txt file.
+
+This style embeds the documentation within the source files, using
+a few simple conventions.  The scripts/kernel-doc perl script, some
+SGML templates in Documentation/DocBook, and other tools understand
+these conventions, and are used to extract this embedded documentation
+into various documents.
+
+In order to provide good documentation of kernel functions and data
+structures, please use the following conventions to format your
+kernel-doc comments in Linux kernel source.
+
+We definitely need kernel-doc formatted documentation for functions
+that are exported to loadable modules using EXPORT_SYMBOL.
+
+We also look to provide kernel-doc formatted documentation for
+functions externally visible to other kernel files (not marked
+"static").
+
+We also recommend providing kernel-doc formatted documentation
+for private (file "static") routines, for consistency of kernel
+source code layout.  But this is lower priority and at the
+discretion of the MAINTAINER of that kernel source file.
+
+Data structures visible in kernel include files should also be
+documented using kernel-doc formatted comments.
+
+The opening comment mark "/**" is reserved for kernel-doc comments.
+Only comments so marked will be considered by the kernel-doc scripts,
+and any comment so marked must be in kernel-doc format.  Do not use
+"/**" to be begin a comment block unless the comment block contains
+kernel-doc formatted comments.  The closing comment marker for
+kernel-doc comments can be either "*/" or "**/".
+
+Kernel-doc comments should be placed just before the function
+or data structure being described.
+
+Example kernel-doc function comment:
+
+/**
+ * foobar() - short function description of foobar
+ * @arg1:	Describe the first argument to foobar.
+ * @arg2:	Describe the second argument to foobar.
+ *		One can provide multiple line descriptions
+ *		for arguments.
+ *
+ * A longer description, with more discussion of the function foobar()
+ * that might be useful to those using or modifying it.  Begins with
+ * empty comment line, and may include additional embedded empty
+ * comment lines.
+ *
+ * The longer description can have multiple paragraphs.
+ **/
+
+The first line, with the short description, must be on a single line.
+
+The @argument descriptions must begin on the very next line following
+this opening short function description line, with no intervening
+empty comment lines.
+
+Example kernel-doc data structure comment.
+
+/**
+ * struct blah - the basic blah structure
+ * @mem1:	describe the first member of struct blah
+ * @mem2:	describe the second member of struct blah,
+ *		perhaps with more lines and words.
+ *
+ * Longer description of this structure.
+ **/
+
+The kernel-doc function comments describe each parameter to the
+function, in order, with the @name lines.
+
+The kernel-doc data structure comments describe each structure member
+in the data structure, with the @name lines.
+
+The longer description formatting is "reflowed", losing your line
+breaks.  So presenting carefully formatted lists within these
+descriptions won't work so well; derived documentation will lose
+the formatting.
+
+See the section below "How to add extractable documentation to your
+source files" for more details and notes on how to format kernel-doc
+comments.
+
+Components of the kernel-doc system
+-----------------------------------
+
 Many places in the source tree have extractable documentation in the
 form of block comments above functions.  The components of this system
 are:
diff --git a/Documentation/kernel-docs.txt b/Documentation/kernel-docs.txt
index 5a4ef48224ae..28cdc2af2131 100644
--- a/Documentation/kernel-docs.txt
+++ b/Documentation/kernel-docs.txt
@@ -715,14 +715,14 @@
 
      * Name: "Gary's Encyclopedia - The Linux Kernel"
        Author: Gary (I suppose...).
-       URL: http://www.lisoleg.net/cgi-bin/lisoleg.pl?view=kernel.htm
-       Keywords: links, not found here?.
+       URL: http://slencyclopedia.berlios.de/index.html
+       Keywords: linux, community, everything!
        Description: Gary's Encyclopedia exists to allow the rapid finding
        of documentation and other information of interest to GNU/Linux
        users. It has about 4000 links to external pages in 150 major
        categories. This link is for kernel-specific links, documents,
-       sites... Look there if you could not find here what you were
-       looking for.
+       sites...  This list is now hosted by developer.Berlios.de,
+       but seems not to have been updated since sometime in 1999.
 
      * Name: "The home page of Linux-MM"
        Author: The Linux-MM team.
diff --git a/Documentation/kobject.txt b/Documentation/kobject.txt
index bf3256e04027..51a8021ee532 100644
--- a/Documentation/kobject.txt
+++ b/Documentation/kobject.txt
@@ -305,7 +305,7 @@ should not be manipulated by any other user.
 
 A kset keeps its children in a standard kernel linked list.  Kobjects point
 back to their containing kset via their kset field. In almost all cases,
-the kobjects belonging to a ket have that kset (or, strictly, its embedded
+the kobjects belonging to a kset have that kset (or, strictly, its embedded
 kobject) in their parent.
 
 As a kset contains a kobject within it, it should always be dynamically
diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index 01c6c3d8a7e3..64b3f146e4b0 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -503,7 +503,7 @@ generate input device EV_KEY events.
 In addition to the EV_KEY events, thinkpad-acpi may also issue EV_SW
 events for switches:
 
-SW_RADIO	T60 and later hardare rfkill rocker switch
+SW_RFKILL_ALL	T60 and later hardare rfkill rocker switch
 SW_TABLET_MODE	Tablet ThinkPads HKEY events 0x5009 and 0x500A
 
 Non hot-key ACPI HKEY event map:
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 3be8ab2a886a..82fafe0429fe 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -157,6 +157,9 @@ struct virtqueue
 
 	/* The routine to call when the Guest pings us. */
 	void (*handle_output)(int fd, struct virtqueue *me);
+
+	/* Outstanding buffers */
+	unsigned int inflight;
 };
 
 /* Remember the arguments to the program so we can "reboot" */
@@ -702,6 +705,7 @@ static unsigned get_vq_desc(struct virtqueue *vq,
 			errx(1, "Looped descriptor");
 	} while ((i = next_desc(vq, i)) != vq->vring.num);
 
+	vq->inflight++;
 	return head;
 }
 
@@ -719,6 +723,7 @@ static void add_used(struct virtqueue *vq, unsigned int head, int len)
 	/* Make sure buffer is written before we update index. */
 	wmb();
 	vq->vring.used->idx++;
+	vq->inflight--;
 }
 
 /* This actually sends the interrupt for this virtqueue */
@@ -726,8 +731,9 @@ static void trigger_irq(int fd, struct virtqueue *vq)
 {
 	unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
 
-	/* If they don't want an interrupt, don't send one. */
-	if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+	/* If they don't want an interrupt, don't send one, unless empty. */
+	if ((vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+	    && vq->inflight)
 		return;
 
 	/* Send the Guest an interrupt tell them we used something up. */
@@ -1107,6 +1113,7 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
 	vq->next = NULL;
 	vq->last_avail_idx = 0;
 	vq->dev = dev;
+	vq->inflight = 0;
 
 	/* Initialize the configuration. */
 	vq->config.num = num_descs;
@@ -1368,6 +1375,7 @@ static void setup_tun_net(const char *arg)
 
 	/* Tell Guest what MAC address to use. */
 	add_feature(dev, VIRTIO_NET_F_MAC);
+	add_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
 	set_config(dev, sizeof(conf), &conf);
 
 	/* We don't need the socket any more; setup is done. */
diff --git a/Documentation/networking/arcnet.txt b/Documentation/networking/arcnet.txt
index 770fc41a78e8..796012540386 100644
--- a/Documentation/networking/arcnet.txt
+++ b/Documentation/networking/arcnet.txt
@@ -46,7 +46,7 @@ These are the ARCnet drivers for Linux.
 
 
 This new release (2.91) has been put together by David Woodhouse 
-<dwmw2@cam.ac.uk>, in an attempt to tidy up the driver after adding support 
+<dwmw2@infradead.org>, in an attempt to tidy up the driver after adding support
 for yet another chipset. Now the generic support has been separated from the
 individual chipset drivers, and the source files aren't quite so packed with
 #ifdefs! I've changed this file a bit, but kept it in the first person from
diff --git a/Documentation/networking/bridge.txt b/Documentation/networking/bridge.txt
index bdae2db4119c..bec69a8a1697 100644
--- a/Documentation/networking/bridge.txt
+++ b/Documentation/networking/bridge.txt
@@ -1,6 +1,6 @@
 In order to use the Ethernet bridging functionality, you'll need the
 userspace tools. These programs and documentation are available
-at http://bridge.sourceforge.net.  The download page is
+at http://www.linux-foundation.org/en/Net:Bridge.  The download page is
 http://prdownloads.sourceforge.net/bridge.
 
 If you still have questions, don't hesitate to post to the mailing list 
diff --git a/Documentation/video4linux/CARDLIST.cx88 b/Documentation/video4linux/CARDLIST.cx88
index 543957346469..7cf5685d3645 100644
--- a/Documentation/video4linux/CARDLIST.cx88
+++ b/Documentation/video4linux/CARDLIST.cx88
@@ -60,7 +60,7 @@
  59 -> DViCO FusionHDTV 5 PCI nano                         [18ac:d530]
  60 -> Pinnacle Hybrid PCTV                                [12ab:1788]
  61 -> Winfast TV2000 XP Global                            [107d:6f18]
- 62 -> PowerColor Real Angel 330                           [14f1:ea3d]
+ 62 -> PowerColor RA330                                    [14f1:ea3d]
  63 -> Geniatech X8000-MT DVBT                             [14f1:8852]
  64 -> DViCO FusionHDTV DVB-T PRO                          [18ac:db30]
  65 -> DViCO FusionHDTV 7 Gold                             [18ac:d610]
diff --git a/Documentation/video4linux/cx18.txt b/Documentation/video4linux/cx18.txt
index 077d56ec3f3d..6842c262890f 100644
--- a/Documentation/video4linux/cx18.txt
+++ b/Documentation/video4linux/cx18.txt
@@ -1,7 +1,9 @@
 Some notes regarding the cx18 driver for the Conexant CX23418 MPEG
 encoder chip:
 
-1) The only hardware currently supported is the Hauppauge HVR-1600.
+1) The only hardware currently supported is the Hauppauge HVR-1600
+   card and the Compro VideoMate H900 (note that this card only
+   supports analog input, it has no digital tuner!).
 
 2) Some people have problems getting the i2c bus to work. Cause unknown.
    The symptom is that the eeprom cannot be read and the card is
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
new file mode 100644
index 000000000000..ce72c0fe6177
--- /dev/null
+++ b/Documentation/vm/pagemap.txt
@@ -0,0 +1,77 @@
+pagemap, from the userspace perspective
+---------------------------------------
+
+pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow
+userspace programs to examine the page tables and related information by
+reading files in /proc.
+
+There are three components to pagemap:
+
+ * /proc/pid/pagemap.  This file lets a userspace process find out which
+   physical frame each virtual page is mapped to.  It contains one 64-bit
+   value for each virtual page, containing the following data (from
+   fs/proc/task_mmu.c, above pagemap_read):
+
+    * Bits 0-55  page frame number (PFN) if present
+    * Bits 0-4   swap type if swapped
+    * Bits 5-55  swap offset if swapped
+    * Bits 55-60 page shift (page size = 1<<page shift)
+    * Bit  61    reserved for future use
+    * Bit  62    page swapped
+    * Bit  63    page present
+
+   If the page is not present but in swap, then the PFN contains an
+   encoding of the swap file number and the page's offset into the
+   swap. Unmapped pages return a null PFN. This allows determining
+   precisely which pages are mapped (or in swap) and comparing mapped
+   pages between processes.
+
+   Efficient users of this interface will use /proc/pid/maps to
+   determine which areas of memory are actually mapped and llseek to
+   skip over unmapped regions.
+
+ * /proc/kpagecount.  This file contains a 64-bit count of the number of
+   times each page is mapped, indexed by PFN.
+
+ * /proc/kpageflags.  This file contains a 64-bit set of flags for each
+   page, indexed by PFN.
+
+   The flags are (from fs/proc/proc_misc, above kpageflags_read):
+
+     0. LOCKED
+     1. ERROR
+     2. REFERENCED
+     3. UPTODATE
+     4. DIRTY
+     5. LRU
+     6. ACTIVE
+     7. SLAB
+     8. WRITEBACK
+     9. RECLAIM
+    10. BUDDY
+
+Using pagemap to do something useful:
+
+The general procedure for using pagemap to find out about a process' memory
+usage goes like this:
+
+ 1. Read /proc/pid/maps to determine which parts of the memory space are
+    mapped to what.
+ 2. Select the maps you are interested in -- all of them, or a particular
+    library, or the stack or the heap, etc.
+ 3. Open /proc/pid/pagemap and seek to the pages you would like to examine.
+ 4. Read a u64 for each page from pagemap.
+ 5. Open /proc/kpagecount and/or /proc/kpageflags.  For each PFN you just
+    read, seek to that entry in the file, and read the data you want.
+
+For example, to find the "unique set size" (USS), which is the amount of
+memory that a process is using that is not shared with any other process,
+you can go through every map in the process, find the PFNs, look those up
+in kpagecount, and tally up the number of pages that are only referenced
+once.
+
+Other notes:
+
+Reading from any of the files will return -EINVAL if you are not starting
+the read on an 8-byte boundary (e.g., if you seeked an odd number of bytes
+into the file), or if the size of the read is not a multiple of 8 bytes.