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From: Andrew Morton <akpm@linux-foundation.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@infradead.org
Subject: Re: [PATCHSET v2 0/3] Improve IOCB_NOWAIT O_DIRECT reads
Date: Tue, 9 Feb 2021 11:55:42 -0800	[thread overview]
Message-ID: <20210209115542.3e407e306a4f1af29257c8f6@linux-foundation.org> (raw)
In-Reply-To: <20210209023008.76263-1-axboe@kernel.dk>

On Mon,  8 Feb 2021 19:30:05 -0700 Jens Axboe <axboe@kernel.dk> wrote:

> Hi,
> 
> For v1, see:
> 
> https://lore.kernel.org/linux-fsdevel/20210208221829.17247-1-axboe@kernel.dk/
> 
> tldr; don't -EAGAIN IOCB_NOWAIT dio reads just because we have page cache
> entries for the given range. This causes unnecessary work from the callers
> side, when the IO could have been issued totally fine without blocking on
> writeback when there is none.
> 

Seems a good idea.  Obviously we'll do more work in the case where some
writeback needs doing, but we'll be doing synchronous writeout in that
case anyway so who cares.

Please remind me what prevents pages from becoming dirty during or
immediately after the filemap_range_needs_writeback() check?  Perhaps
filemap_range_needs_writeback() could have a comment explaining what it
is that keeps its return value true after it has returned it!

  parent reply	other threads:[~2021-02-09 21:21 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  2:30 [PATCHSET v2 0/3] Improve IOCB_NOWAIT O_DIRECT reads Jens Axboe
2021-02-09  2:30 ` [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper Jens Axboe
2021-02-09  7:47   ` Christoph Hellwig
2021-02-09 14:30     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 2/3] mm: use filemap_range_needs_writeback() for O_DIRECT reads Jens Axboe
2021-02-09  7:48   ` Christoph Hellwig
2021-02-09 14:27     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 3/3] iomap: " Jens Axboe
2021-02-09  7:51   ` Christoph Hellwig
2021-02-09 14:29     ` Jens Axboe
2021-02-09 19:55 ` Andrew Morton [this message]
2021-02-09 20:11   ` [PATCHSET v2 0/3] Improve IOCB_NOWAIT " Jens Axboe
2021-02-10  8:07     ` Sedat Dilek
2021-02-10  8:07       ` Sedat Dilek
2021-02-10 14:47       ` Jens Axboe

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