[PATCH RESEND] 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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