[PATCH] Documentation: Describe the shared memory usage/accounting

[Rodrigo Freire]

The Shared Memory accounting support is present in Kernel since 
commit 4b02108ac1b3 ("mm: oom analysis: add shmem vmstat") and in userland
free(1) since 2014. This patch updates the Documentation to reflect
this change.

Signed-off-by: Rodrigo Freire <rfreire@xxxxxxxxxx> 
---
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -842,6 +842,7 @@
 Writeback:           0 kB
 AnonPages:      861800 kB
 Mapped:         280372 kB
+Shmem:             644 kB
 Slab:           284364 kB
 SReclaimable:   159856 kB
 SUnreclaim:     124508 kB
@@ -898,6 +899,7 @@
    AnonPages: Non-file backed pages mapped into userspace page tables
 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
       Mapped: files which have been mmaped, such as libraries
+       Shmem: Total memory used by shared memory (shmem) and tmpfs
         Slab: in-kernel data structures cache
 SReclaimable: Part of Slab, that might be reclaimed, such as caches
   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
--- a/Documentation/filesystems/tmpfs.txt
+++ b/Documentation/filesystems/tmpfs.txt
@@ -17,10 +17,10 @@
 cannot swap and you do not have the possibility to resize them. 
 
 Since tmpfs lives completely in the page cache and on swap, all tmpfs
-pages currently in memory will show up as cached. It will not show up
-as shared or something like that. Further on you can check the actual
-RAM+swap use of a tmpfs instance with df(1) and du(1).
-
+pages will be shown in /proc/meminfo as "Shmem" and "Shared" in
+free(1). Notice that shared memory pages (see ipcs(1)) will be also
+counted as shared memory. The most reliable way to get the count is
+using df(1) and du(1).
 
 tmpfs has the following uses:
 
---
1.7.1
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