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From: Sedat Dilek <sedat.dilek@gmail.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	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: Wed, 10 Feb 2021 09:07:44 +0100	[thread overview]
Message-ID: <CA+icZUWBrHA72gQzyByKbNeCzaaVcNX85VwnYHozp6KWBt5tHQ@mail.gmail.com> (raw)
In-Reply-To: <32dba5cc-7878-3b7b-45e4-84690a45a998@kernel.dk>

On Tue, Feb 9, 2021 at 10:25 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 2/9/21 12:55 PM, Andrew Morton wrote:
> > 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.
>
> Right, I think that'll be a round two on top of this, so we can make the
> write side happier too. That's a bit more involved...
>
> > 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!
>
> It's inherently racy, just like it is now. There's really no difference
> there, and I don't think there's a way to close that. Even if you
> modified filemap_write_and_wait_range() to be non-block friendly,
> there's nothing stopping anyone from adding dirty page cache right after
> that call.
>

Jens, do you have some numbers before and after your patchset is applied?

And kindly a test "profile" for FIO :-)?

Thanks.

- Sedat -

  reply	other threads:[~2021-02-10  8:09 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  2:30 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 ` [PATCHSET v2 0/3] Improve IOCB_NOWAIT " Andrew Morton
2021-02-09 20:11   ` Jens Axboe
2021-02-10  8:07     ` Sedat Dilek [this message]
2021-02-10  8:07       ` Sedat Dilek
2021-02-10 14:47       ` Jens Axboe

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