mm: smaps: split PSS into components

Report separate components (anon, file, and shmem) for PSS in
smaps_rollup.

This helps understand and tune the memory manager behavior in consumer
devices, particularly mobile devices.  Many of them (e.g.  chromebooks and
Android-based devices) use zram for anon memory, and perform disk reads
for discarded file pages.  The difference in latency is large (e.g.
reading a single page from SSD is 30 times slower than decompressing a
zram page on one popular device), thus it is useful to know how much of
the PSS is anon vs.  file.

All the information is already present in /proc/pid/smaps, but much more
expensive to obtain because of the large size of that procfs entry.

This patch also removes a small code duplication in smaps_account, which
would have gotten worse otherwise.

Also updated Documentation/filesystems/proc.txt (the smaps section was a
bit stale, and I added a smaps_rollup section) and
Documentation/ABI/testing/procfs-smaps_rollup.

[semenzato@chromium.org: v5]
  Link: http://lkml.kernel.org/r/20190626234333.44608-1-semenzato@chromium.org
Link: http://lkml.kernel.org/r/20190626180429.174569-1-semenzato@chromium.org
Signed-off-by: Luigi Semenzato <semenzato@chromium.org>
Acked-by: Yu Zhao <yuzhao@chromium.org>
Cc: Sonny Rao <sonnyrao@chromium.org>
Cc: Yu Zhao <yuzhao@chromium.org>
Cc: Brian Geffon <bgeffon@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 43 insertions, 12 deletions

diff --git a/Documentation/ABI/testing/procfs-smaps_rollup b/Documentation/ABI/testing/procfs-smaps_rollup
index 0a54ed0d63c9..274df44d8b1b 100644
--- a/Documentation/ABI/testing/procfs-smaps_rollup
+++ b/Documentation/ABI/testing/procfs-smaps_rollup
@@ -3,18 +3,28 @@ Date:		August 2017
 Contact:	Daniel Colascione <dancol@google.com>
 Description:
 		This file provides pre-summed memory information for a
-		process.  The format is identical to /proc/pid/smaps,
+		process.  The format is almost identical to /proc/pid/smaps,
 		except instead of an entry for each VMA in a process,
 		smaps_rollup has a single entry (tagged "[rollup]")
 		for which each field is the sum of the corresponding
 		fields from all the maps in /proc/pid/smaps.
-		For more details, see the procfs man page.
+		Additionally, the fields Pss_Anon, Pss_File and Pss_Shmem
+		are not present in /proc/pid/smaps.  These fields represent
+		the sum of the Pss field of each type (anon, file, shmem).
+		For more details, see Documentation/filesystems/proc.txt
+		and the procfs man page.
 
 		Typical output looks like this:
 
 		00100000-ff709000 ---p 00000000 00:00 0		 [rollup]
+		Size:               1192 kB
+		KernelPageSize:        4 kB
+		MMUPageSize:           4 kB
 		Rss:		     884 kB
 		Pss:		     385 kB
+		Pss_Anon:	     301 kB
+		Pss_File:	      80 kB
+		Pss_Shmem:	       4 kB
 		Shared_Clean:	     696 kB
 		Shared_Dirty:	       0 kB
 		Private_Clean:	     120 kB
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index a226061fa109..d750b6926899 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -154,9 +154,11 @@ Table 1-1: Process specific entries in /proc
 		symbol the task is blocked in - or "0" if not blocked.
  pagemap	Page table
  stack		Report full stack trace, enable via CONFIG_STACKTRACE
- smaps		an extension based on maps, showing the memory consumption of
+ smaps		An extension based on maps, showing the memory consumption of
 		each mapping and flags associated with it
- numa_maps	an extension based on maps, showing the memory locality and
+ smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
+		can be derived from smaps, but is faster and more convenient
+ numa_maps	An extension based on maps, showing the memory locality and
 		binding policy as well as mem usage (in pages) of each mapping.
 ..............................................................................
 
@@ -366,7 +368,7 @@ Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
   exit_code     the thread's exit_code in the form reported by the waitpid system call
 ..............................................................................
 
-The /proc/PID/maps file containing the currently mapped memory regions and
+The /proc/PID/maps file contains the currently mapped memory regions and
 their access permissions.
 
 The format is:
@@ -417,11 +419,14 @@ is not associated with a file:
  or if empty, the mapping is anonymous.
 
 The /proc/PID/smaps is an extension based on maps, showing the memory
-consumption for each of the process's mappings. For each of mappings there
-is a series of lines such as the following:
+consumption for each of the process's mappings. For each mapping (aka Virtual
+Memory Area, or VMA) there is a series of lines such as the following:
 
 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
+
 Size:               1084 kB
+KernelPageSize:        4 kB
+MMUPageSize:           4 kB
 Rss:                 892 kB
 Pss:                 374 kB
 Shared_Clean:        892 kB
@@ -443,11 +448,14 @@ Locked:                0 kB
 THPeligible:           0
 VmFlags: rd ex mr mw me dw
 
-the first of these lines shows the same information as is displayed for the
-mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
-(size), the amount of the mapping that is currently resident in RAM (RSS), the
-process' proportional share of this mapping (PSS), the number of clean and
-dirty private pages in the mapping.
+The first of these lines shows the same information as is displayed for the
+mapping in /proc/PID/maps.  Following lines show the size of the mapping
+(size); the size of each page allocated when backing a VMA (KernelPageSize),
+which is usually the same as the size in the page table entries; the page size
+used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
+the amount of the mapping that is currently resident in RAM (RSS); the
+process' proportional share of this mapping (PSS); and the number of clean and
+dirty shared and private pages in the mapping.
 
 The "proportional set size" (PSS) of a process is the count of pages it has
 in memory, where each page is divided by the number of processes sharing it.
@@ -532,6 +540,19 @@ guarantees:
 2) If there is something at a given vaddr during the entirety of the
    life of the smaps/maps walk, there will be some output for it.
 
+The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
+but their values are the sums of the corresponding values for all mappings of
+the process.  Additionally, it contains these fields:
+
+Pss_Anon
+Pss_File
+Pss_Shmem
+
+They represent the proportional shares of anonymous, file, and shmem pages, as
+described for smaps above.  These fields are omitted in smaps since each
+mapping identifies the type (anon, file, or shmem) of all pages it contains.
+Thus all information in smaps_rollup can be derived from smaps, but at a
+significantly higher cost.
 
 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 bits on both physical and virtual pages associated with a process, and the