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From: Jens Axboe <axboe@kernel.dk>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
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: Sun, 11 Jul 2021 19:44:07 -0600	[thread overview]
Message-ID: <a3d0f8da-ffb4-25a3-07a1-79987ce788c5@kernel.dk> (raw)
In-Reply-To: <20210711150927.3898403-1-willy@infradead.org>

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.

-- 
Jens Axboe



  parent reply	other threads:[~2021-07-12  1:44 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 ` Jens Axboe [this message]
2021-07-24 18:22   ` [PATCH 0/2] Close a hole where IOCB_NOWAIT reads could sleep Matthew Wilcox
2021-07-24 19:46     ` Jens Axboe

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