From: Jens Axboe <firstname.lastname@example.org> To: Matthew Wilcox <email@example.com>, Lin Feng <firstname.lastname@example.org> Cc: Michal Hocko <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Omar Sandoval <email@example.com>, Ming Lei <firstname.lastname@example.org> Subject: Re: Is congestion broken? Date: Mon, 23 Sep 2019 13:38:23 -0600 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20190923111900.GH15392@bombadil.infradead.org> On 9/23/19 5:19 AM, Matthew Wilcox wrote: > > 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? Congestion isn't there anymore. It was always broken as a concept imho, since it was inherently racy. We used the old batching mechanism in the legacy stack to signal it, and it only worked for some devices. -- Jens Axboe
next prev parent reply other threads:[~2019-09-23 19:38 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 ` Is congestion broken? Matthew Wilcox 2019-09-23 19:38 ` Jens Axboe [this message] 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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