From: Matthew Wilcox <willy@infradead.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Dave Chinner <david@fromorbit.com>,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 1/2] fs: Add IOCB_NOIO flag for generic_file_read_iter
Date: Fri, 3 Jul 2020 12:41:08 +0100 [thread overview]
Message-ID: <20200703114108.GE25523@casper.infradead.org> (raw)
In-Reply-To: <20200703095325.1491832-2-agruenba@redhat.com>
On Fri, Jul 03, 2020 at 11:53:24AM +0200, Andreas Gruenbacher wrote:
> Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it
> shouldn't trigger any filesystem I/O for the actual request or for
> readahead. This allows to do tentative reads out of the page cache as
> some filesystems allow, and to take the appropriate locks and retry the
> reads only if the requested pages are not cached.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> @@ -2249,9 +2253,18 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read);
> *
> * This is the "read_iter()" routine for all filesystems
> * that can use the page cache directly.
> + *
> + * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
> + * be returned when no data can be read without waiting for I/O requests
> + * to complete; it doesn't prevent readahead.
> + *
> + * The IOCB_NOIO flag in iocb->ki_flags indicates that -EAGAIN shall be
> + * returned when no data can be read without issuing new I/O requests,
> + * and 0 shall be returned when readhead would have been triggered.
s/shall/may/ -- if we read a previous page then hit a readahead page,
we'll return a positive value. If the first page we hit is a readahead
page, then yes, we'll return zero.
Again, I'm happy for the patch to go in as-is without this nitpick.
next prev parent reply other threads:[~2020-07-03 11:41 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-03 9:53 [RFC v2 0/2] Fix gfs2 readahead deadlocks Andreas Gruenbacher
2020-07-03 9:53 ` [RFC v2 1/2] fs: Add IOCB_NOIO flag for generic_file_read_iter Andreas Gruenbacher
2020-07-03 11:41 ` Matthew Wilcox [this message]
2020-07-05 15:08 ` Andreas Gruenbacher
2020-07-03 9:53 ` [RFC v2 2/2] gfs2: Rework read and page fault locking Andreas Gruenbacher
2020-07-03 11:38 ` Matthew Wilcox
2020-07-03 11:44 ` Matthew Wilcox
2020-07-03 19:24 ` [RFC v2 0/2] Fix gfs2 readahead deadlocks Linus Torvalds
2020-07-03 19:26 ` Linus Torvalds
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