Re: [PATCH] proc.5: statm's "shared" field refers to pages backed by files.

I noticed that statm's "shared" field doesn't match the sum of all the
"shared" entries in smaps [1].

The kernel docs explain that statm's "shared" field is "number of
pages that are shared (i.e. backed by a file)" [2].  smaps appears to
call a page shared if it's mapped by at least two processes, which
explains this discrepancy.

I'm not a kernel hacker, but it appears to me they do mean "i.e." and
not "e.g." in the statm description: In
fs/proc/task_mmu.c::task_statm, I see

    *shared = get_mm_counter(mm, MM_FILEPAGES);

Here's a patch which updates the man page to match the (hopefully
correct) kernel docs.

Subject: [PATCH] proc.5: statm's "shared" field refers to pages backed by
 files.

---
 man5/proc.5 |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/man5/proc.5 b/man5/proc.5
index 88af7c5..855a2e0 100644
--- a/man5/proc.5
+++ b/man5/proc.5

@@ -947,7 +947,7 @@ size       total program size
            (same as VmSize in \fI/proc/[pid]/status\fP)
 resident   resident set size
            (same as VmRSS in \fI/proc/[pid]/status\fP)
-share      shared pages (from shared mappings)
+share      shared pages (i.e., backed by a file)
 text       text (code)
 .\" (not including libs; broken, includes data segment)
 lib        library (unused in Linux 2.6)
--

1.7.10.4

I've also attached the patch in case gmail messes it up somehow.

-Justin

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=807181
[2] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=Documentation/filesystems/proc.txt;h=a1793d670cd01bd374eddf54ffdfc768504291ff;hb=HEAD