From: Jens Axboe <[email protected]>
To: "Matthew Wilcox (Oracle)" <[email protected]>
Cc: [email protected], [email protected],
[email protected], [email protected]
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: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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
next prev 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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