From: Ming Lei <ming.lei@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Ming Lei <tom.leiming@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Dave Chinner <david@fromorbit.com>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
"open list:XFS FILESYSTEM" <linux-xfs@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Dave Chinner <dchinner@redhat.com>,
Christoph Hellwig <hch@lst.de>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Aaron Lu <aaron.lu@intel.com>, Christopher Lameter <cl@linux.com>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
linux-block <linux-block@vger.kernel.org>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc
Date: Tue, 26 Feb 2019 20:35:46 +0800 [thread overview]
Message-ID: <20190226123545.GA6163@ming.t460p> (raw)
In-Reply-To: <20190226121209.GC11592@bombadil.infradead.org>
On Tue, Feb 26, 2019 at 04:12:09AM -0800, Matthew Wilcox wrote:
> On Tue, Feb 26, 2019 at 07:12:49PM +0800, Ming Lei wrote:
> > On Tue, Feb 26, 2019 at 6:07 PM Vlastimil Babka <vbabka@suse.cz> wrote:
> > > On 2/26/19 10:33 AM, Ming Lei wrote:
> > > > On Tue, Feb 26, 2019 at 03:58:26PM +1100, Dave Chinner wrote:
> > > >> On Mon, Feb 25, 2019 at 07:27:37PM -0800, Matthew Wilcox wrote:
> > > >>> On Tue, Feb 26, 2019 at 02:02:14PM +1100, Dave Chinner wrote:
> > > >>>>> Or what is the exact size of sub-page IO in xfs most of time? For
> > > >>>>
> > > >>>> Determined by mkfs parameters. Any power of 2 between 512 bytes and
> > > >>>> 64kB needs to be supported. e.g:
> > > >>>>
> > > >>>> # mkfs.xfs -s size=512 -b size=1k -i size=2k -n size=8k ....
> > > >>>>
> > > >>>> will have metadata that is sector sized (512 bytes), filesystem
> > > >>>> block sized (1k), directory block sized (8k) and inode cluster sized
> > > >>>> (32k), and will use all of them in large quantities.
> > > >>>
> > > >>> If XFS is going to use each of these in large quantities, then it doesn't
> > > >>> seem unreasonable for XFS to create a slab for each type of metadata?
> > > >>
> > > >>
> > > >> Well, that is the question, isn't it? How many other filesystems
> > > >> will want to make similar "don't use entire pages just for 4k of
> > > >> metadata" optimisations as 64k page size machines become more
> > > >> common? There are others that have the same "use slab for sector
> > > >> aligned IO" which will fall foul of the same problem that has been
> > > >> reported for XFS....
> > > >>
> > > >> If nobody else cares/wants it, then it can be XFS only. But it's
> > > >> only fair we address the "will it be useful to others" question
> > > >> first.....
> > > >
> > > > This kind of slab cache should have been global, just like interface of
> > > > kmalloc(size).
> > > >
> > > > However, the alignment requirement depends on block device's block size,
> > > > then it becomes hard to implement as genera interface, for example:
> > > >
> > > > block size: 512, 1024, 2048, 4096
> > > > slab size: 512*N, 0 < N < PAGE_SIZE/512
> > > >
> > > > For 4k page size, 28(7*4) slabs need to be created, and 64k page size
> > > > needs to create 127*4 slabs.
> > > >
> > >
> > > Where does the '*4' multiplier come from?
> >
> > The buffer needs to be device block size aligned for dio, and now the block
> > size can be 512, 1024, 2048 and 4096.
>
> Why does the block size make a difference? This requirement is due to
> some storage devices having shoddy DMA controllers. Are you saying there
> are devices which can't even do 512-byte aligned I/O?
Direct IO requires that, see do_blockdev_direct_IO().
This issue can be triggered when running xfs over loop/dio. We could
fallback to buffered IO under this situation, but not sure it is the
only case.
Thanks,
Ming
next prev parent reply other threads:[~2019-02-26 12:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-25 4:09 [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc Ming Lei
2019-02-25 4:36 ` Dave Chinner
2019-02-25 8:46 ` Ming Lei
2019-02-25 10:03 ` Ming Lei
2019-02-25 20:11 ` Dave Chinner
2019-02-25 13:15 ` Vlastimil Babka
2019-02-25 20:26 ` Dave Chinner
2019-02-26 2:22 ` Ming Lei
2019-02-26 3:02 ` Dave Chinner
2019-02-26 3:27 ` Matthew Wilcox
2019-02-26 4:58 ` Dave Chinner
2019-02-26 9:33 ` Ming Lei
2019-02-26 10:06 ` Vlastimil Babka
2019-02-26 11:12 ` Ming Lei
2019-02-26 12:12 ` Matthew Wilcox
2019-02-26 12:35 ` Ming Lei [this message]
2019-02-26 13:02 ` Matthew Wilcox
2019-02-26 13:42 ` Ming Lei
2019-02-26 14:04 ` Matthew Wilcox
2019-02-26 16:14 ` Darrick J. Wong
2019-02-26 16:19 ` Matthew Wilcox
2019-02-27 1:41 ` Ming Lei
2019-02-27 7:07 ` Vlastimil Babka
2019-03-08 8:18 ` Christoph Hellwig
2019-02-27 21:38 ` Dave Chinner
2019-02-26 15:30 ` Christopher Lameter
2019-02-26 20:45 ` Dave Chinner
2019-02-27 1:50 ` Ming Lei
2019-02-27 3:41 ` Dave Chinner
2019-02-26 15:20 ` Christopher Lameter
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