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

From: Rodrigo Freire
Date: Thu Nov 19 2015 - 13:58:27 EST

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:

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