Re: [patch 1/1] vmscan: give referenced, active and unmapped pages a second trip around the LRU

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 25 May 2007 10:43:49 -0400 Rik van Riel <riel@redhat.com> wrote:

> akpm@linux-foundation.org wrote:
> > From: Andrew Morton <akpm@linux-foundation.org>
> > 
> > Martin spotted this.
> > 
> > In the original rmap conversion in 2.5.32 we broke aging of pagecache pages on
> > the active list: we deactivate these pages even if they had PG_referenced set.
> 
> IIRC this is done to make sure that we reclaim page cache pages
> ahead of mapped anonymous pages.

I think it was an accident.  At least, that 2.5.32 change was uncommented
and unchangelogged and was an inappropriate thing to have been bundled into
that patch.

> > We should instead clear PG_referenced and give these pages another trip around
> > the active list.
> 
> A side effect of this is that the page will now need TWO references
> to be promoted back to the active list from the inactive list.
> 
> The current code leaves PG_referenced set, so that the first access
> to a page cache page that was demoted to the inactive list will cause
> that page to be moved back to the active list.

hm, yeah, we should be setting PG-referenced when moving a page from the
active list onto the inactive list.

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