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Date:   Tue, 19 Apr 2022 10:17:55 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: [PATCH v2] fs-writeback: =?utf-8?Q?wri?=
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On Mon, Apr 18, 2022 at 12:43:43PM -0700, Linus Torvalds wrote:
> Which all brings us back to how we have that hacky thing in
> writeback_sb_inodes() that does
> 
>         if (need_resched()) {
>                 /*
>                  * We're trying to balance between building up a nice
>                  * long list of IOs to improve our merge rate, and
>                  * getting those IOs out quickly for anyone throttling
>                  * in balance_dirty_pages().  cond_resched() doesn't
>                  * unplug, so get our IOs out the door before we
>                  * give up the CPU.
>                  */
>                 blk_flush_plug(current->plug, false);
>                 cond_resched();
>         }

Yeah, that's horribly broken for PREEMPT=y.