From: Ming Lei <ming.lei@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
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@kvack.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc
Date: Tue, 26 Feb 2019 10:22:50 +0800 [thread overview]
Message-ID: <20190226022249.GA17747@ming.t460p> (raw)
In-Reply-To: <20190225202630.GG23020@dastard>
On Tue, Feb 26, 2019 at 07:26:30AM +1100, Dave Chinner wrote:
> On Mon, Feb 25, 2019 at 02:15:59PM +0100, Vlastimil Babka wrote:
> > On 2/25/19 5:36 AM, Dave Chinner wrote:
> > > On Mon, Feb 25, 2019 at 12:09:04PM +0800, Ming Lei wrote:
> > >> XFS uses kmalloc() to allocate sector sized IO buffer.
> > > ....
> > >> Use page_frag_alloc() to allocate the sector sized buffer, then the
> > >> above issue can be fixed because offset_in_page of allocated buffer
> > >> is always sector aligned.
> > >
> > > Didn't we already reject this approach because page frags cannot be
> > > reused and that pages allocated to the frag pool are pinned in
> > > memory until all fragments allocated on the page have been freed?
> >
> > I don't know if you did, but it's certainly true., Also I don't think
> > there's any specified alignment guarantee for page_frag_alloc().
>
> We did, and the alignment guarantee would have come from all
> fragments having an aligned size.
>
> > What about kmem_cache_create() with align parameter? That *should* be
> > guaranteed regardless of whatever debugging is enabled - if not, I would
> > consider it a bug.
>
> Yup, that's pretty much what was decided. The sticking point was
> whether is should be block layer infrastructure (because the actual
> memory buffer alignment is a block/device driver requirement not
> visible to the filesystem) or whether "sector size alignement is
> good enough for everyone".
OK, looks I miss the long life time of meta data caching, then let's
discuss the slab approach.
Looks one single slab cache doesn't work, given the size may be 512 * N
(1 <= N < PAGE_SIZE/512), that is basically what I posted the first
time.
https://marc.info/?t=153986884900007&r=1&w=2
https://marc.info/?t=153986885100001&r=1&w=2
Or what is the exact size of sub-page IO in xfs most of time? For
example, if 99% times falls in 512 byte allocation, maybe it is enough
to just maintain one 512byte slab.
Thanks,
Ming
next prev parent reply other threads:[~2019-02-26 2:23 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 [this message]
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
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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