From: "Wilcox, Matthew R" <matthew.r.wilcox@intel.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: "linda.knippers@hp.com" <linda.knippers@hp.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: RE: regression introduced by "block: Add support for DAX reads/writes to block devices"
Date: Thu, 6 Aug 2015 15:51:56 +0000 [thread overview]
Message-ID: <100D68C7BA14664A8938383216E40DE040914111@FMSMSX114.amr.corp.intel.com> (raw)
In-Reply-To: <x49pp30ig86.fsf@segfault.boston.devel.redhat.com>
Yes, that's the result I want. Fundamentally, I think DAX should be able to support devices that are not multiples of PAGE_SIZE in size.
-----Original Message-----
From: Jeff Moyer [mailto:jmoyer@redhat.com]
Sent: Thursday, August 06, 2015 8:34 AM
To: Wilcox, Matthew R
Cc: linda.knippers@hp.com; linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org
Subject: Re: regression introduced by "block: Add support for DAX reads/writes to block devices"
"Wilcox, Matthew R" <matthew.r.wilcox@intel.com> writes:
> I think I see the problem. I'm kind of wrapped up in other things
> right now; can you try replacing the line in dax_io():
>
> - bh->b_size = PAGE_ALIGN(end - pos);
> + bh->b_size = ALIGN(end - pos, 1 << blkbits);
That's not gonna work either. :) You'll end up with -EINVAL since
bdev_direct_access wants the sector to be aligned to a page:
if (sector % (PAGE_SIZE / 512))
return -EINVAL;
I think you really want to call direct_access with the full page, and
then tease out the part you want up in dax_io, right? I'll take a crack
at it if you're busy.
Cheers,
Jeff
> -----Original Message-----
> From: Jeff Moyer [mailto:jmoyer@redhat.com]
> Sent: Wednesday, August 05, 2015 1:19 PM
> To: Wilcox, Matthew R; linda.knippers@hp.com
> Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org
> Subject: regression introduced by "block: Add support for DAX reads/writes to block devices"
>
> Hi, Matthew,
>
> Linda Knippers noticed that commit (bbab37ddc20b) breaks mkfs.xfs:
>
> # mkfs -t xfs -f /dev/pmem0
> meta-data=/dev/pmem0 isize=256 agcount=4, agsize=524288 blks
> = sectsz=512 attr=2, projid32bit=1
> = crc=0 finobt=0
> data = bsize=4096 blocks=2097152, imaxpct=25
> = sunit=0 swidth=0 blks
> naming =version 2 bsize=4096 ascii-ci=0 ftype=0
> log =internal log bsize=4096 blocks=2560, version=2
> = sectsz=512 sunit=0 blks, lazy-count=1
> realtime =none extsz=4096 blocks=0, rtextents=0
> mkfs.xfs: read failed: Numerical result out of range
>
> I sat down with Linda to look into it, and the problem is that mkfs.xfs
> sets the blocksize of the device to 512 (via BLKBSZSET), and then reads
> from the last sector of the device. This results in dax_io trying to do
> a page-sized I/O at 512 bytes from the end of the device.
> bdev_direct_access, receiving this bogus pos/size combo, returns
> -ERANGE:
>
> if ((sector + DIV_ROUND_UP(size, 512)) >
> part_nr_sects_read(bdev->bd_part))
> return -ERANGE;
>
> Given that file systems supporting dax refuse to mount with a blocksize
> != page size, I'm guessing this is sort of expected behavior. However,
> we really shouldn't be breaking direct I/O on pmem devices.
>
> So, what do you want to do? We could make the pmem device's logical
> block size fixed at the sytem page size. Or, we could modify the dax
> code to work with blocksize < pagesize. Or, we could continue using the
> direct I/O codepath for direct block device access. What do you think?
>
> Thaks,
> Jeff and Linda
next prev parent reply other threads:[~2015-08-06 15:52 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-05 20:19 regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer
2015-08-05 22:01 ` Dave Chinner
2015-08-06 1:42 ` Linda Knippers
2015-08-06 3:24 ` Dave Chinner
2015-08-06 7:52 ` Boaz Harrosh
2015-08-06 20:34 ` Dave Chinner
2015-08-09 8:52 ` Boaz Harrosh
2015-08-10 16:32 ` Linda Knippers
2015-08-10 21:27 ` Dave Chinner
2015-08-10 23:04 ` Linda Knippers
2015-08-06 14:21 ` Wilcox, Matthew R
2015-08-06 15:33 ` Jeff Moyer
2015-08-06 15:51 ` Wilcox, Matthew R [this message]
2015-08-06 21:30 ` Jeff Moyer
2015-08-07 18:11 ` Wilcox, Matthew R
2015-08-07 20:41 ` Jeff Moyer
2015-08-10 7:42 ` Boaz Harrosh
2015-08-12 21:11 ` Jeff Moyer
2015-08-13 5:32 ` Boaz Harrosh
2015-08-13 14:00 ` Jeff Moyer
2015-08-13 16:42 ` Linda Knippers
2015-08-13 17:14 ` Jeff Moyer
2015-08-13 17:52 ` Linda Knippers
2015-08-13 18:19 ` Jeff Moyer
2015-08-13 19:32 ` Wilcox, Matthew R
2015-08-14 16:28 ` Dan Williams
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