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Re: [PATCH 4/5] mm: vmscan: Immediately reclaim end-of-LRU dirty pages w

To: Johannes Weiner <jweiner@xxxxxxxxxx>
Subject: Re: [PATCH 4/5] mm: vmscan: Immediately reclaim end-of-LRU dirty pages when writeback completes
From: Mel Gorman <mgorman@xxxxxxx>
Date: Wed, 13 Jul 2011 18:15:53 +0100
Cc: Linux-MM <linux-mm@xxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, XFS <xfs@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>
In-reply-to: <20110713164040.GA13972@xxxxxxxxxx>
References: <1310567487-15367-1-git-send-email-mgorman@xxxxxxx> <1310567487-15367-5-git-send-email-mgorman@xxxxxxx> <20110713164040.GA13972@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Jul 13, 2011 at 06:40:40PM +0200, Johannes Weiner wrote:
> On Wed, Jul 13, 2011 at 03:31:26PM +0100, Mel Gorman wrote:
> > When direct reclaim encounters a dirty page, it gets recycled around
> > the LRU for another cycle. This patch marks the page PageReclaim using
> > deactivate_page() so that the page gets reclaimed almost immediately
> > after the page gets cleaned. This is to avoid reclaiming clean pages
> > that are younger than a dirty page encountered at the end of the LRU
> > that might have been something like a use-once page.
> > 
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> > ---
> >  include/linux/mmzone.h |    2 +-
> >  mm/vmscan.c            |   10 ++++++++--
> >  mm/vmstat.c            |    2 +-
> >  3 files changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index c4508a2..bea7858 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -100,7 +100,7 @@ enum zone_stat_item {
> >     NR_UNSTABLE_NFS,        /* NFS unstable pages */
> >     NR_BOUNCE,
> >     NR_VMSCAN_WRITE,
> > -   NR_VMSCAN_WRITE_SKIP,
> > +   NR_VMSCAN_INVALIDATE,
> >     NR_VMSCAN_THROTTLED,
> >     NR_WRITEBACK_TEMP,      /* Writeback using temporary buffers */
> >     NR_ISOLATED_ANON,       /* Temporary isolated pages from anon lru */
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 9826086..8e00aee 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -834,8 +834,13 @@ static unsigned long shrink_page_list(struct list_head 
> > *page_list,
> >                      */
> >                     if (page_is_file_cache(page) &&
> >                                     (!current_is_kswapd() || priority >= 
> > DEF_PRIORITY - 2)) {
> > -                           inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP);
> > -                           goto keep_locked;
> > +                           inc_zone_page_state(page, NR_VMSCAN_INVALIDATE);
> > +
> > +                           /* Immediately reclaim when written back */
> > +                           unlock_page(page);
> > +                           deactivate_page(page);
> > +
> > +                           goto keep_dirty;
> >                     }
> >  
> >                     if (references == PAGEREF_RECLAIM_CLEAN)
> > @@ -956,6 +961,7 @@ keep:
> >             reset_reclaim_mode(sc);
> >  keep_lumpy:
> >             list_add(&page->lru, &ret_pages);
> > +keep_dirty:
> >             VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> >     }
> 
> I really like the idea behind this patch, but I think all those pages
> are lost as PageLRU is cleared on isolation and lru_deactivate_fn
> bails on them in turn.
> 
> If I'm not mistaken, the reference from the isolation is also leaked.

I think you're right. This patch was rushed and not thought through
properly.  The surprise it appeared to work at all. Will rework
it. Thanks.

-- 
Mel Gorman
SUSE Labs

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