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From: NeilBrown <neilb@suse.de>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>,
	linux-mm@kvack.org, linux-nfs@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 1/2 V3] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE
Date: Wed, 13 May 2020 17:16:32 +1000	[thread overview]
Message-ID: <871rnob8z3.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20200422124600.GH8775@quack2.suse.cz>

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I thought about this some more and come up with another "simple"
approach that didn't require me understanding too much code, but does -
I think - address your concerns.

I've changed the heuristic to avoid any throttling on PF_LOCAL_THROTTLE
task if:
 - the global dirty count is below the global free-run threshold.  The
   code did this already.
 - (or) the per-wb dirty count is below the per-wb free-run threshold.
   This is the change.

This means that:
 - in a steady stated, all bdis will be throttled based on their (steady
   state) throughput, which is equally appropriate for PF_LOCAL_THROTTLE
   tasks.
 - a PF_LOCAL_THROTTLE task will never be *completely* blocked by dirty
   pages queued for other devices.  This means no deadlock, and that is
   the primary purpose of PF_LOCAL_THROTTLE.
 - when writes through the PF_LOCAL_THROTTLE task start up from idle -
   when there is no current throughput estimate - the PF_LOCAL_THROTTLE
   can be expected to get a fair share of the available memory, just as
   much as any other writer.  This was the possible problem with
   treating PF_LOCAL_THROTTLE just like BDI_CAP_STRICTLIMIT.

So I think this is a good solution.  Thoughts?
Patches follow - I've address the comment formatting issue.

Thanks,
NeilBrown

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  reply	other threads:[~2020-05-13  7:16 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26  3:25 [PATCH/RFC] MM: fix writeback for NFS NeilBrown
2020-04-01 23:52 ` Writeback fixes " NeilBrown
2020-04-01 23:53   ` [PATCH 1/2] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE NeilBrown
2020-04-01 23:54     ` [PATCH 2/2] Deprecate NR_UNSTABLE_NFS, use NR_WRITEBACK NeilBrown
2020-04-02 15:10       ` Christoph Hellwig
2020-04-02 22:35         ` [PATCH 2/2 - v2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead NeilBrown
2020-04-03  9:42           ` Jan Kara
2020-04-03 11:03             ` Michal Hocko
2020-04-06  0:14               ` NeilBrown
2020-04-06  7:41                 ` Michal Hocko
2020-04-06 23:28             ` NeilBrown
2020-04-07  7:33               ` Michal Hocko
2020-04-02 19:55       ` [PATCH 2/2] Deprecate NR_UNSTABLE_NFS, use NR_WRITEBACK Jan Kara
2020-04-02 16:35     ` [PATCH 1/2] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE Jan Kara
2020-04-03 15:15     ` Michal Hocko
2020-04-03 21:40       ` NeilBrown
2020-04-06  7:44         ` Michal Hocko
2020-04-06  9:36           ` Jan Kara
2020-04-06 10:57             ` Michal Hocko
2020-04-06 11:58             ` NeilBrown
2020-04-02  4:26   ` Hillf Danton
2020-04-02  4:57     ` NeilBrown
2020-04-06  3:58     ` Hillf Danton
2020-04-06 23:42   ` Writeback fixes for NFS - V2 NeilBrown
2020-04-06 23:42     ` NeilBrown
2020-04-06 23:43     ` [PATCH 1/2] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE NeilBrown
2020-04-06 23:43       ` NeilBrown
2020-04-07 16:10       ` Chuck Lever
2020-04-16  0:29     ` Writeback fixes for NFS - V3 NeilBrown
2020-04-16  0:30       ` [PATCH 1/2 V3] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE NeilBrown
2020-04-16  6:54         ` Christoph Hellwig
2020-04-16 15:19         ` Jan Kara
2020-04-21  2:22           ` NeilBrown
2020-04-22 12:46             ` Jan Kara
2020-05-13  7:16               ` NeilBrown [this message]
2020-05-13  7:17                 ` [PATCH 1/2 V4] " NeilBrown
2020-05-15 11:10                   ` Jan Kara
2020-06-01  0:46                     ` Writeback fixes for NFS NeilBrown
2020-06-01  0:48                       ` [PATCH 1/2] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE NeilBrown
2020-06-01  0:49                       ` [PATCH 2/2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead NeilBrown
2020-05-13  7:18                 ` [PATCH 2/2 V4] " NeilBrown
2020-05-15  9:59                   ` Jan Kara
2020-04-16  0:31       ` [PATCH 2/2 V3] " NeilBrown
2020-04-16  6:56         ` Christoph Hellwig
2020-04-16 15:24         ` Jan Kara

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