From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
Goldwyn Rodrigues <rgoldwyn@suse.de>,
jack@suse.com, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 3/8] nowait aio: return if direct write will trigger writeback
Date: Thu, 2 Mar 2017 06:12:45 -0800 [thread overview]
Message-ID: <20170302141245.GO16328@bombadil.infradead.org> (raw)
In-Reply-To: <20170302103845.GB31792@quack2.suse.cz>
On Thu, Mar 02, 2017 at 11:38:45AM +0100, Jan Kara wrote:
> On Wed 01-03-17 07:38:57, Christoph Hellwig wrote:
> > On Tue, Feb 28, 2017 at 07:46:06PM -0800, Matthew Wilcox wrote:
> > > But what's going to kick these pages out of cache? Shouldn't we rather
> > > find the pages, kick them out if clean, start writeback if not, and *then*
> > > return -EAGAIN?
> >
> > As pointed out in the last round of these patches I think we really
> > need to pass a flags argument to filemap_write_and_wait_range to
> > communicate the non-blocking nature and only return -EAGAIN if we'd
> > block. As a bonus that can indeed start to kick the pages out.
>
> Aren't flags to filemap_write_and_wait_range() unnecessary complication?
> Realistically, most users wanting performance from AIO DIO so badly that
> they bother with this API won't have any pages to write / evict. If they do
> by some bad accident, they can fall back to standard "blocking" AIO DIO.
> So I don't see much value in teaching filemap_write_and_wait_range() about
> a non-blocking mode...
That lets me execute a DoS against a user using this API. All I have
to do is open the file they're using read-only and read a byte from it.
Page goes into page-cache, and they'll only get -EAGAIN from calling
this syscall until the page ages out.
Also, I don't understand why this is a flag. Isn't the point of AIO to
be non-blocking? Why isn't this just a change to how we do AIO?
next prev parent reply other threads:[~2017-03-02 14:17 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-28 23:36 [PATCH 0/8 v2] Non-blocking AIO Goldwyn Rodrigues
2017-02-28 23:36 ` [PATCH 1/8] nowait aio: Introduce IOCB_FLAG_NOWAIT Goldwyn Rodrigues
2017-03-01 15:36 ` Christoph Hellwig
2017-03-01 15:56 ` Christoph Hellwig
2017-03-01 16:57 ` Goldwyn Rodrigues
2017-03-01 22:44 ` Christoph Hellwig
2017-02-28 23:36 ` [PATCH 2/8] nowait aio: Return if cannot get hold of i_rwsem Goldwyn Rodrigues
2017-03-01 15:37 ` Christoph Hellwig
2017-02-28 23:36 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-03-01 3:46 ` Matthew Wilcox
2017-03-01 15:38 ` Christoph Hellwig
2017-03-02 10:38 ` Jan Kara
2017-03-02 14:12 ` Matthew Wilcox [this message]
2017-03-02 15:22 ` Jan Kara
2017-02-28 23:36 ` [PATCH 4/8] nowait aio: Introduce IOMAP_NOWAIT Goldwyn Rodrigues
2017-02-28 23:36 ` [PATCH 5/8] nowait aio: return on congested block device Goldwyn Rodrigues
2017-03-08 7:03 ` Sagi Grimberg
2017-03-08 15:00 ` Goldwyn Rodrigues
2017-03-08 15:28 ` Jan Kara
2017-03-08 15:51 ` Christoph Hellwig
2017-03-08 16:17 ` Jens Axboe
2017-03-09 2:18 ` Goldwyn Rodrigues
2017-02-28 23:36 ` [PATCH 6/8] nowait aio: ext4 Goldwyn Rodrigues
2017-02-28 23:36 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-03-01 15:40 ` Christoph Hellwig
2017-02-28 23:36 ` [PATCH 8/8] nowait aio: btrfs Goldwyn Rodrigues
2017-03-05 14:56 ` [PATCH 0/8 v2] Non-blocking AIO Avi Kivity
2017-03-06 8:25 ` Jan Kara
2017-03-06 8:40 ` Avi Kivity
2017-03-06 15:19 ` Jens Axboe
2017-03-06 15:29 ` Avi Kivity
2017-03-06 15:38 ` Jens Axboe
2017-03-06 15:59 ` Avi Kivity
2017-03-06 16:08 ` Jens Axboe
2017-03-06 16:59 ` Avi Kivity
2017-03-06 17:06 ` Jens Axboe
2017-03-06 18:17 ` Avi Kivity
2017-03-06 18:27 ` Jens Axboe
2017-03-06 18:50 ` Avi Kivity
2017-03-15 21:50 [PATCH 0/8 v3] No wait AIO Goldwyn Rodrigues
2017-03-15 21:51 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-03-16 13:08 ` Matthew Wilcox
2017-03-16 13:46 ` Goldwyn Rodrigues
2017-03-16 13:20 ` Matthew Wilcox
2017-03-16 13:46 ` Goldwyn Rodrigues
2017-04-03 18:52 [PATCH 0/8 v4] No wait AIO Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-04-14 12:02 [PATCH 0/8 v6] No wait AIO Goldwyn Rodrigues
2017-04-14 12:02 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-05-09 12:22 [PATCH 0/8 v7] No wait AIO Goldwyn Rodrigues
2017-05-09 12:22 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-05-11 7:42 ` Christoph Hellwig
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