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From: Matthew Wilcox <willy@infradead.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-aio@kvack.org
Subject: Re: [PATCH 0/2] Close a hole where IOCB_NOWAIT reads could sleep
Date: Sat, 24 Jul 2021 19:22:20 +0100	[thread overview]
Message-ID: <YPxaXE0mf26aqy/O@casper.infradead.org> (raw)
In-Reply-To: <a3d0f8da-ffb4-25a3-07a1-79987ce788c5@kernel.dk>

On Sun, Jul 11, 2021 at 07:44:07PM -0600, Jens Axboe wrote:
> On 7/11/21 9:09 AM, Matthew Wilcox (Oracle) wrote:
> > I noticed a theoretical case where an IOCB_NOWAIT read could sleep:
> > 
> > filemap_get_pages
> >   filemap_get_read_batch
> >   page_cache_sync_readahead
> >     page_cache_sync_ra
> >       ondemand_readahead
> >         do_page_cache_ra
> >         page_cache_ra_unbounded
> >           gfp_t gfp_mask = readahead_gfp_mask(mapping);
> >           memalloc_nofs_save()
> >           __page_cache_alloc(gfp_mask);
> > 
> > We're in a nofs context, so we're not going to start new IO, but we might
> > wait for writeback to complete.  We generally don't want to sleep for IO,
> > particularly not for IO that isn't related to us.
> > 
> > Jens, can you run this through your test rig and see if it makes any
> > practical difference?
> 
> You bet, I'll see if I can trigger this condition and verify we're no
> longer blocking on writeback. Thanks for hacking this up.

Did you have any success yet?

  reply	other threads:[~2021-07-24 18:22 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-11 15:09 [PATCH 0/2] Close a hole where IOCB_NOWAIT reads could sleep Matthew Wilcox (Oracle)
2021-07-11 15:09 ` [PATCH 1/2] mm/readahead: Add gfp_flags to ractl Matthew Wilcox (Oracle)
2021-07-12 11:34   ` Christoph Hellwig
2021-07-12 14:37     ` Matthew Wilcox
2021-07-11 15:09 ` [PATCH 2/2] mm/filemap: Prevent waiting for memory for NOWAIT reads Matthew Wilcox (Oracle)
2021-07-12  1:44 ` [PATCH 0/2] Close a hole where IOCB_NOWAIT reads could sleep Jens Axboe
2021-07-24 18:22   ` Matthew Wilcox [this message]
2021-07-24 19:46     ` Jens Axboe

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