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Date: Thu, 29 Sep 2022 17:58:41 -0600 From: Jens Axboe <axboe@...nel.dk> To: Hugh Dickins <hughd@...gle.com> Cc: Keith Busch <kbusch@...nel.org>, linux-block@...r.kernel.org, Liu Song <liusong@...ux.alibaba.com>, Hillf Danton <hdanton@...a.com>, Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org, Yu Kuai <yukuai1@...weicloud.com> Subject: Re: [PATCH next v3] sbitmap: fix lockup while swapping On Thu, 29 Sep 2022 12:50:12 -0700 (PDT), Hugh Dickins wrote: > Commit 4acb83417cad ("sbitmap: fix batched wait_cnt accounting") > is a big improvement: without it, I had to revert to before commit > 040b83fcecfb ("sbitmap: fix possible io hung due to lost wakeup") > to avoid the high system time and freezes which that had introduced. > > Now okay on the NVME laptop, but 4acb83417cad is a disaster for heavy > swapping (kernel builds in low memory) on another: soon locking up in > sbitmap_queue_wake_up() (into which __sbq_wake_up() is inlined), cycling > around with waitqueue_active() but wait_cnt 0 . Here is a backtrace, > showing the common pattern of outer sbitmap_queue_wake_up() interrupted > before setting wait_cnt 0 back to wake_batch (in some cases other CPUs > are idle, in other cases they're spinning for a lock in dd_bio_merge()): > > [...] Applied, thanks! [1/1] sbitmap: fix lockup while swapping commit: 30514bd2dd4e86a3ecfd6a93a3eadf7b9ea164a0 Best regards, -- Jens Axboe
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