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From: Matthew Wilcox <willy@infradead.org>
To: Lin Feng <linf@wangsu.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	corbet@lwn.net, mcgrof@kernel.org, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	keescook@chromium.org, mchehab+samsung@kernel.org,
	mgorman@techsingularity.net, vbabka@suse.cz,
	ktkhai@virtuozzo.com, hannes@cmpxchg.org,
	Jens Axboe <axboe@kernel.dk>, Omar Sandoval <osandov@fb.com>,
	Ming Lei <ming.lei@redhat.com>
Subject: Is congestion broken?
Date: Mon, 23 Sep 2019 04:19:00 -0700	[thread overview]
Message-ID: <20190923111900.GH15392@bombadil.infradead.org> (raw)
In-Reply-To: <20190919034949.GF9880@bombadil.infradead.org>


Ping Jens?

On Wed, Sep 18, 2019 at 08:49:49PM -0700, Matthew Wilcox wrote:
> On Thu, Sep 19, 2019 at 10:33:10AM +0800, Lin Feng wrote:
> > On 9/18/19 20:33, Michal Hocko wrote:
> > > I absolutely agree here. From you changelog it is also not clear what is
> > > the underlying problem. Both congestion_wait and wait_iff_congested
> > > should wake up early if the congestion is handled. Is this not the case?
> > 
> > For now I don't know why, codes seem should work as you said, maybe I need to
> > trace more of the internals.
> > But weird thing is that once I set the people-disliked-tunable iowait
> > drop down instantly, this is contradictory to the code design.
> 
> Yes, this is quite strange.  If setting a smaller timeout makes a
> difference, that indicates we're not waking up soon enough.  I see
> two possibilities; one is that a wakeup is missing somewhere -- ie the
> conditions under which we call clear_wb_congested() are wrong.  Or we
> need to wake up sooner.
> 
> Umm.  We have clear_wb_congested() called from exactly one spot --
> clear_bdi_congested().  That is only called from:
> 
> drivers/block/pktcdvd.c
> fs/ceph/addr.c
> fs/fuse/control.c
> fs/fuse/dev.c
> fs/nfs/write.c
> 
> Jens, is something supposed to be calling clear_bdi_congested() in the
> block layer?  blk_clear_congested() used to exist until October 29th
> last year.  Or is something else supposed to be waking up tasks that
> are sleeping on congestion?
> 
> 


  parent reply	other threads:[~2019-09-23 11:19 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-17 11:58 [PATCH] [RFC] vmscan.c: add a sysctl entry for controlling memory reclaim IO congestion_wait length Lin Feng
2019-09-17 12:06 ` Matthew Wilcox
2019-09-18  3:21   ` Lin Feng
2019-09-18 11:38     ` Matthew Wilcox
2019-09-19  2:20       ` Lin Feng
2019-09-18 12:33   ` Michal Hocko
2019-09-19  2:33     ` Lin Feng
2019-09-19  3:49       ` Matthew Wilcox
2019-09-19  7:46         ` Lin Feng
2019-09-19  8:22           ` Michal Hocko
2019-09-23 11:19         ` Matthew Wilcox [this message]
2019-09-23 19:38           ` Is congestion broken? Jens Axboe
2019-09-23 19:45             ` Matthew Wilcox
2019-09-23 19:51               ` Jens Axboe
2019-09-24 12:16                 ` Michal Hocko

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