From: Matthew Wilcox <willy@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Ming Lei <ming.lei@redhat.com>, Ming Lei <tom.leiming@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Dave Chinner <david@fromorbit.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 08:19:12 -0800 [thread overview]
Message-ID: <20190226161912.GG11592@bombadil.infradead.org> (raw)
In-Reply-To: <20190226161433.GH21626@magnolia>
On Tue, Feb 26, 2019 at 08:14:33AM -0800, Darrick J. Wong wrote:
> On Tue, Feb 26, 2019 at 06:04:40AM -0800, Matthew Wilcox wrote:
> > On Tue, Feb 26, 2019 at 09:42:48PM +0800, Ming Lei wrote:
> > > On Tue, Feb 26, 2019 at 05:02:30AM -0800, Matthew Wilcox wrote:
> > > > Wait, we're imposing a ridiculous amount of complexity on XFS for no
> > > > reason at all? We should just change this to 512-byte alignment. Tying
> > > > it to the blocksize of the device never made any sense.
> > >
> > > OK, that is fine since we can fallback to buffered IO for loop in case of
> > > unaligned dio.
> > >
> > > Then something like the following patch should work for all fs, could
> > > anyone comment on this approach?
> >
> > That's not even close to what I meant.
> >
> > diff --git a/fs/direct-io.c b/fs/direct-io.c
> > index ec2fb6fe6d37..dee1fc47a7fc 100644
> > --- a/fs/direct-io.c
> > +++ b/fs/direct-io.c
> > @@ -1185,18 +1185,20 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
>
> Wait a minute, are you all saying that /directio/ is broken on XFS too??
> XFS doesn't use blockdev_direct_IO anymore.
>
> I thought we were talking about alignment of XFS metadata buffers
> (xfs_buf.c), which is a very different topic.
>
> As I understand the problem, in non-debug mode the slab caches give
> xfs_buf chunks of memory that are aligned well enough to work, but in
> debug mode the slabs allocate slightly more bytes to carry debug
> information which pushes the returned address up slightly, thus breaking
> the alignment requirements.
>
> So why can't we just move the debug info to the end of the object? If
> our 512 byte allocation turns into a (512 + a few more) bytes we'll end
> up using 1024 bytes on the allocation regardless, so it shouldn't matter
> to put the debug info at offset 512. If the reason is fear that kernel
> code will scribble off the end of the object, then return (*obj + 512).
> Maybe you all have already covered this, though?
I don't know _what_ Ming Lei is saying. I thought the problem was
with slab redzones, which need to be before and after each object,
but apparently the problem is with KASAN as well.
next prev parent reply other threads:[~2019-02-26 16:19 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
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 [this message]
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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