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

[Johannes Weiner <jweiner@redhat.com>]

On Mon, Nov 07, 2011 at 11:34:17AM +0900, KAMEZAWA Hiroyuki wrote:
> 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..

Do you mean an extra LRU list that holds dirty pages?