linux-kernel - Re: [PATCH 0/3] idle memory tracking

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Date:	Tue, 24 Mar 2015 10:45:45 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Minchan Kim <minchan@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Jonathan Corbet <corbet@....net>, <linux-api@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] idle memory tracking

On Wed, Mar 18, 2015 at 11:44:33PM +0300, Vladimir Davydov wrote:
> Usage:
> 
>  1. Write 1 to /proc/sys/vm/set_idle.
> 
>     This will set the IDLE flag for all user pages. The IDLE flag is cleared
>     when the page is read or the ACCESS/YOUNG bit is cleared in any PTE pointing
>     to the page. It is also cleared when the page is freed.
> 
>  2. Wait some time.
> 
>  3. Write 6 to /proc/PID/clear_refs for each PID of interest.
> 
>     This will clear the IDLE flag for recently accessed pages.
> 
>  4. Count the number of idle pages as reported by /proc/kpageflags. One may use
>     /proc/PID/pagemap and/or /proc/kpagecgroup to filter pages that belong to a
>     certain application/container.

Any more thoughts on this? I am particularly interested in the user
interface. I think that /proc/kpagecgroup is OK, but I have my
reservations about using /proc/sys/vm/set_idle and /proc/PID/clear_refs
for setting and clearing the idle flag. The point is it is impossible to
scan memory for setting/clearing page idle flags in the background with
some predefined rate - one has to scan it all at once, which might
result in CPU load spikes on huge machines with TBs of RAM. May be, we'd
better introduce /proc/sys/vm/{set_idle,clear_refs_idle}, which would
receive pfn range to set/clear idle flags?

Any thoughts/ideas are more than welcome.

Thanks,
Vladimir
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