From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: NeilBrown <neilb@suse.de>, "Theodore Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
"Darrick J . Wong" <djwong@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>,
Dave Chinner <david@fromorbit.com>,
Rik van Riel <riel@surriel.com>, Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Jonathan Corbet <corbet@lwn.net>, Linux-MM <linux-mm@kvack.org>,
Linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 0/8] Remove dependency on congestion_wait in mm/
Date: Tue, 19 Oct 2021 15:00:25 -0700 [thread overview]
Message-ID: <20211019150025.c62a0c72538d1f9fa20f1e81@linux-foundation.org> (raw)
In-Reply-To: <20211019090108.25501-1-mgorman@techsingularity.net>
On Tue, 19 Oct 2021 10:01:00 +0100 Mel Gorman <mgorman@techsingularity.net> wrote:
> Changelog since v3
> o Count writeback completions for NR_THROTTLED_WRITTEN only
> o Use IRQ-safe inc_node_page_state
> o Remove redundant throttling
>
> This series is also available at
>
> git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-reclaimcongest-v4r2
>
> This series that removes all calls to congestion_wait
> in mm/ and deletes wait_iff_congested. It's not a clever
> implementation but congestion_wait has been broken for a long time
> (https://lore.kernel.org/linux-mm/45d8b7a6-8548-65f5-cccf-9f451d4ae3d4@kernel.dk/).
The block layer doesn't call clear_bdi_congested() at all. I never
knew this until recent discussions :(
So this means that congestion_wait() will always time out, yes?
> Even if congestion throttling worked, it was never a great idea.
Well. It was a good idea until things like isolation got added!
> While
> excessive dirty/writeback pages at the tail of the LRU is one possibility
> that reclaim may be slow, there is also the problem of too many pages
> being isolated and reclaim failing for other reasons (elevated references,
> too many pages isolated, excessive LRU contention etc).
>
> This series replaces the "congestion" throttling with 3 different types.
>
> o If there are too many dirty/writeback pages, sleep until a timeout
> or enough pages get cleaned
> o If too many pages are isolated, sleep until enough isolated pages
> are either reclaimed or put back on the LRU
> o If no progress is being made, direct reclaim tasks sleep until
> another task makes progress with acceptable efficiency.
>
> This was initially tested with a mix of workloads that used to trigger
> corner cases that no longer work.
Mix of workloads is nice, but a mix of devices is more important here.
I trust some testing was done on plain old spinning disks? And USB
storage, please! And NFS plays with BDI congestion. Ceph and FUSE also.
We've had complaints about this stuff forever. Usually of the form of
interactive tasks getting horridly stalled by writeout/swap activity.
next prev parent reply other threads:[~2021-10-19 22:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 9:01 [PATCH v4 0/8] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-10-19 9:01 ` [PATCH 1/8] mm/vmscan: Throttle reclaim until some writeback completes if congested Mel Gorman
2021-10-19 9:01 ` [PATCH 2/8] mm/vmscan: Throttle reclaim and compaction when too may pages are isolated Mel Gorman
2021-10-19 17:12 ` Yang Shi
2021-10-19 9:01 ` [PATCH 3/8] mm/vmscan: Throttle reclaim when no progress is being made Mel Gorman
2021-10-19 9:01 ` [PATCH 4/8] mm/writeback: Throttle based on page writeback instead of congestion Mel Gorman
2021-10-19 9:01 ` [PATCH 5/8] mm/page_alloc: Remove the throttling logic from the page allocator Mel Gorman
2021-10-19 9:20 ` Vlastimil Babka
2021-10-19 9:01 ` [PATCH 6/8] mm/vmscan: Centralise timeout values for reclaim_throttle Mel Gorman
2021-10-22 1:06 ` NeilBrown
2021-10-22 8:12 ` Mel Gorman
2021-10-19 9:01 ` [PATCH 7/8] mm/vmscan: Increase the timeout if page reclaim is not making progress Mel Gorman
2021-10-22 1:07 ` NeilBrown
2021-10-22 8:14 ` Mel Gorman
2021-10-19 9:01 ` [PATCH 8/8] mm/vmscan: Delay waking of tasks throttled on NOPROGRESS Mel Gorman
2021-10-19 22:00 ` Andrew Morton [this message]
2021-10-20 8:44 ` [PATCH v4 0/8] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-10-22 1:15 ` NeilBrown
2021-10-22 8:39 ` Mel Gorman
2021-10-22 11:26 ` NeilBrown
2021-10-22 13:17 ` Mel Gorman
2021-10-27 0:43 ` NeilBrown
2021-10-27 10:13 ` Mel Gorman
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