Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced
Date	2017-02-05 11:20 +0100
Message-ID	<t7s5k-5Z3-17@gated-at.bofh.it> (permalink)
References	<t6SOe-6J7-11@gated-at.bofh.it> <t7s5k-5Z3-9@gated-at.bofh.it>
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On Sun 05-02-17 11:11:13, Michal Hocko wrote:
> On Fri 03-02-17 20:32:22, Mel Gorman wrote:
> > Hillf Danton pointed out that since commit 1d82de618dd ("mm, vmscan:
> > make kswapd reclaim in terms of nodes") that PGDAT_WRITEBACK is no longer
> > cleared. It was not noticed as triggering it requires pages under writeback
> > to cycle twice through the LRU and before kswapd gets stalled. Historically,
> > such issues tended to occur on small machines writing heavily to slow
> > storage such as a USB stick. Once kswapd stalls, direct reclaim stalls may
> > be higher but due to the fact that memory pressure is requires, it would not
> > be very noticable. Michal Hocko suggested removing the flag entirely but
> > the conservative fix is to restore the intended PGDAT_WRITEBACK behaviour
> > and clear the flag when a suitable zone is balanced.
> > 
> > Signed-off-by: Mel Gorman <mgorman@suse.de>
> 
> I agree this is a more conservative approach but I think removing
> PGDAT_WRITEBACK should simplify things a bit.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>

Ohh, an please add
Fixes: 1d82de618ddd ("mm, vmscan: make kswapd reclaim in terms of nodes")
-- 
Michal Hocko
SUSE Labs

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[PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced Mel Gorman <mgorman@suse.de> - 2017-02-03 21:40 +0100
  Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced Johannes Weiner <hannes@cmpxchg.org> - 2017-02-03 22:30 +0100
  Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-02-04 04:20 +0100
  Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced Michal Hocko <mhocko@kernel.org> - 2017-02-05 11:20 +0100
    Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced Michal Hocko <mhocko@kernel.org> - 2017-02-05 11:20 +0100

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