linux-kernel - Re: [PATCH] mm: show proportional swap share of the mapping

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Date:	Wed, 10 Jun 2015 08:36:11 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Bongkyu Kim <bongkyu.kim@....com>
Subject: Re: [PATCH] mm: show proportional swap share of the mapping

Hello Andrew,

On Tue, Jun 09, 2015 at 02:35:48PM -0700, Andrew Morton wrote:
> On Tue,  9 Jun 2015 23:43:51 +0900 Minchan Kim <minchan@...nel.org> wrote:
> 
> > For system uses swap heavily and has lots of shared anonymous page,
> > it's very trouble to find swap set size per process because currently
> > smaps doesn't report proportional set size of swap.
> > It ends up that sum of the number of swap for all processes is greater
> > than swap device size.
> > 
> > This patch introduces SwapPss field on /proc/<pid>/smaps.
> > 
> 
> We should be told quite a bit more about the value of this change,
> please.  Use cases, what problems it solves, etc.  Enough to justify
> adding new code to the kernel, enough to justify adding yet another
> userspace interface which must be maintained for ever.

The goal is same with present pages's PSS.

We want to know per-process workingset size for smart memory
management by userland platform memory manager. Our products
use swap(ex, zram) heavily to maximize memory efficiency.
IOW, workingset includes rss + swap.

However, without this feature, it's really hard to figure out
how many each process consumes availabe memory(rss + zram-swap)
if the system has lots of shared anonymous memory(e.g, android).

> 
> > --- a/Documentation/filesystems/proc.txt
> > +++ b/Documentation/filesystems/proc.txt
> >
> > ...
> >
> > @@ -441,7 +442,7 @@ indicates the amount of memory currently marked as referenced or accessed.
> >  a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
> >  and a page is modified, the file page is replaced by a private anonymous copy.
> >  "Swap" shows how much would-be-anonymous memory is also used, but out on
> > -swap.
> > +swap. "SwapPss" shows process' proportional swap share of this mapping.
> >  
> >  "VmFlags" field deserves a separate description. This member represents the kernel
> >  flags associated with the particular virtual memory area in two letter encoded
> 
> Documentation/filesystems/proc.txt doesn't actually explain what
> "proportional share" means.  A patient reader will hopefully find the
> comment over PSS_SHIFT in fs/proc/task_mmu.c, but that isn't very
> user-friendly.

Okay, I will try to add more comment about PSS in proc.txt
on next spin if you are not against this feature.

Thanks.

> 
> 
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