Re: [rfc 2/3] mm: vmscan: treat inactive cycling as neutral

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 2 Nov 2011 17:32:13 +0100
Johannes Weiner <jweiner@redhat.com> wrote:

> Each page that is scanned but put back to the inactive list is counted
> as a successful reclaim, which tips the balance between file and anon
> lists more towards the cycling list.
> 
> This does - in my opinion - not make too much sense, but at the same
> time it was not much of a problem, as the conditions that lead to an
> inactive list cycle were mostly temporary - locked page, concurrent
> page table changes, backing device congested - or at least limited to
> a single reclaimer that was not allowed to unmap or meddle with IO.
> More important than being moderately rare, those conditions should
> apply to both anon and mapped file pages equally and balance out in
> the end.
> 
> Recently, we started cycling file pages in particular on the inactive
> list much more aggressively, for used-once detection of mapped pages,
> and when avoiding writeback from direct reclaim.
> 
> Those rotated pages do not exactly speak for the reclaimability of the
> list they sit on and we risk putting immense pressure on file list for
> no good reason.
> 
> Instead, count each page not reclaimed and put back to any list,
> active or inactive, as rotated, so they are neutral with respect to
> the scan/rotate ratio of the list class, as they should be.
> 
> Signed-off-by: Johannes Weiner <jweiner@redhat.com>

I think this makes sense.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

I wonder it may be better to have victim list for written-backed pages..

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