From: Ming Lei <ming.lei@redhat.com>
To: John Garry <john.g.garry@oracle.com>
Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
jejb@linux.ibm.com, martin.petersen@oracle.com,
djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org,
chandan.babu@oracle.com, dchinner@redhat.com,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
linux-api@vger.kernel.org
Subject: Re: [PATCH 10/21] block: Add fops atomic write support
Date: Tue, 5 Dec 2023 09:45:53 +0800 [thread overview]
Message-ID: <ZW6A0R04Gk/04EHj@fedora> (raw)
In-Reply-To: <bd639010-2ad7-4379-ba0a-64b5f6ebec41@oracle.com>
On Mon, Dec 04, 2023 at 01:13:55PM +0000, John Garry wrote:
>
> > >
> > > I added this here (as opposed to the caller), as I was not really worried
> > > about speeding up the failure path. Are you saying to call even earlier in
> > > submission path?
> > atomic_write_unit_min is one hardware property, and it should be checked
> > in blk_queue_atomic_write_unit_min_sectors() from beginning, then you
> > can avoid this check every other where.
>
> ok, but we still need to ensure in the submission path that the block device
> actually supports atomic writes - this was the initial check.
Then you may add one helper bdev_support_atomic_write().
>
> >
> > > > > + if (pos % atomic_write_unit_min_bytes)
> > > > > + return false;
> > > > > + if (iov_iter_count(iter) % atomic_write_unit_min_bytes)
> > > > > + return false;
> > > > > + if (!is_power_of_2(iov_iter_count(iter)))
> > > > > + return false;
> > > > > + if (iov_iter_count(iter) > atomic_write_unit_max_bytes)
> > > > > + return false;
> > > > > + if (pos % iov_iter_count(iter))
> > > > > + return false;
> > > > I am a bit confused about relation between atomic_write_unit_max_bytes and
> > > > atomic_write_max_bytes.
> > > I think that naming could be improved. Or even just drop merging (and
> > > atomic_write_max_bytes concept) until we show it to improve performance.
> > >
> > > So generally atomic_write_unit_max_bytes will be same as
> > > atomic_write_max_bytes, however it could be different if:
> > > a. request queue nr hw segments or other request queue limits needs to
> > > restrict atomic_write_unit_max_bytes
> > > b. atomic_write_unit_max_bytes does not need to be a power-of-2 and
> > > atomic_write_max_bytes does. So essentially:
> > > atomic_write_unit_max_bytes = rounddown_pow_of_2(atomic_write_max_bytes)
> > >
> > plug merge often improves sequential IO perf, so if the hardware supports
> > this way, I think 'atomic_write_max_bytes' should be supported from the
> > beginning, such as:
> >
> > - user space submits sequential N * (4k, 8k, 16k, ...) atomic writes, all can
> > be merged to single IO request, which is issued to driver.
> >
> > Or
> >
> > - user space submits sequential 4k, 4k, 8k, 16K, 32k, 64k atomic writes, all can
> > be merged to single IO request, which is issued to driver.
>
> Right, we do expect userspace to use a fixed block size, but we give scope
> in the API to use variable size.
Maybe it is enough to just take atomic_write_unit_min_bytes
only, and allow length to be N * atomic_write_unit_min_bytes.
But it may violate atomic write boundary?
>
> >
> > The hardware should recognize unit size by start LBA, and check if length is
> > valid, so probably the interface might be relaxed to:
> >
> > 1) start lba is unit aligned, and this unit is in the supported unit
> > range(power_2 in [unit_min, unit_max])
> >
> > 2) length needs to be:
> >
> > - N * this_unit_size
> > - <= atomic_write_max_bytes
>
> Please note that we also need to consider:
> - any atomic write boundary (from NVMe)
Can you provide actual NVMe boundary value?
Firstly natural aligned write won't cross boundary, so boundary should
be >= write_unit_max, see blow code from patch 10/21:
+static bool bio_straddles_atomic_write_boundary(loff_t bi_sector,
+ unsigned int bi_size,
+ unsigned int boundary)
+{
+ loff_t start = bi_sector << SECTOR_SHIFT;
+ loff_t end = start + bi_size;
+ loff_t start_mod = start % boundary;
+ loff_t end_mod = end % boundary;
+
+ if (end - start > boundary)
+ return true;
+ if ((start_mod > end_mod) && (start_mod && end_mod))
+ return true;
+
+ return false;
+}
+
Then if the WRITE size is <= boundary, the above function should return
false, right? Looks like it is power_of(2) & aligned atomic_write_max_bytes?
> - virt boundary (from NVMe)
virt boundary is applied on bv_offset and bv_len, and NVMe's virt
bounary is (4k - 1), it shouldn't be one issue in reality.
>
> And, as I mentioned elsewhere, I am still not 100% comfortable that we don't
> pay attention to regular max_sectors_kb...
max_sectors_kb should be bigger than atomic_write_max_bytes actually,
then what is your concern?
Thanks,
Ming
next prev parent reply other threads:[~2023-12-05 1:46 UTC|newest]
Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-29 10:27 [PATCH 00/21] block atomic writes John Garry
2023-09-29 10:27 ` [PATCH 01/21] block: Add atomic write operations to request_queue limits John Garry
2023-10-03 16:40 ` Bart Van Assche
2023-10-04 3:00 ` Martin K. Petersen
2023-10-04 17:28 ` Bart Van Assche
2023-10-04 18:26 ` Martin K. Petersen
2023-10-04 21:00 ` Bart Van Assche
2023-10-05 8:22 ` John Garry
2023-11-09 15:10 ` Christoph Hellwig
2023-11-09 17:01 ` John Garry
2023-11-10 6:23 ` Christoph Hellwig
2023-11-10 9:04 ` John Garry
2023-09-29 10:27 ` [PATCH 02/21] block: Limit atomic writes according to bio and queue limits John Garry
2023-11-09 15:13 ` Christoph Hellwig
2023-11-09 17:41 ` John Garry
2023-12-04 3:19 ` Ming Lei
2023-12-04 3:55 ` Ming Lei
2023-12-04 9:35 ` John Garry
2023-09-29 10:27 ` [PATCH 03/21] fs/bdev: Add atomic write support info to statx John Garry
2023-09-29 22:49 ` Eric Biggers
2023-10-01 13:23 ` Bart Van Assche
2023-10-02 9:51 ` John Garry
2023-10-02 18:39 ` Bart Van Assche
2023-10-03 0:28 ` Martin K. Petersen
2023-11-09 15:15 ` Christoph Hellwig
2023-10-03 1:51 ` Dave Chinner
2023-10-03 2:57 ` Darrick J. Wong
2023-10-03 7:23 ` John Garry
2023-10-03 15:46 ` Darrick J. Wong
2023-10-04 14:19 ` John Garry
2023-09-29 10:27 ` [PATCH 04/21] fs: Add RWF_ATOMIC and IOCB_ATOMIC flags for atomic write support John Garry
2023-10-06 18:15 ` Jeremy Bongio
2023-10-09 22:02 ` Dave Chinner
2023-09-29 10:27 ` [PATCH 05/21] block: Add REQ_ATOMIC flag John Garry
2023-09-29 10:27 ` [PATCH 06/21] block: Pass blk_queue_get_max_sectors() a request pointer John Garry
2023-09-29 10:27 ` [PATCH 07/21] block: Limit atomic write IO size according to atomic_write_max_sectors John Garry
2023-09-29 10:27 ` [PATCH 08/21] block: Error an attempt to split an atomic write bio John Garry
2023-09-29 10:27 ` [PATCH 09/21] block: Add checks to merging of atomic writes John Garry
2023-09-30 13:40 ` kernel test robot
2023-10-02 22:50 ` Nathan Chancellor
2023-10-04 11:40 ` John Garry
2023-09-29 10:27 ` [PATCH 10/21] block: Add fops atomic write support John Garry
2023-09-29 17:51 ` Bart Van Assche
2023-10-02 10:10 ` John Garry
2023-10-02 19:12 ` Bart Van Assche
2023-10-03 0:48 ` Martin K. Petersen
2023-10-03 16:55 ` Bart Van Assche
2023-10-04 2:53 ` Martin K. Petersen
2023-10-04 17:22 ` Bart Van Assche
2023-10-04 18:17 ` Martin K. Petersen
2023-10-05 17:10 ` Bart Van Assche
2023-10-05 22:36 ` Dave Chinner
2023-10-05 22:58 ` Bart Van Assche
2023-10-06 4:31 ` Dave Chinner
2023-10-06 17:22 ` Bart Van Assche
2023-10-07 1:21 ` Martin K. Petersen
2023-10-03 8:37 ` John Garry
2023-10-03 16:45 ` Bart Van Assche
2023-10-04 9:14 ` John Garry
2023-10-04 17:34 ` Bart Van Assche
2023-10-04 21:59 ` Dave Chinner
2023-12-04 2:30 ` Ming Lei
2023-12-04 9:27 ` John Garry
2023-12-04 12:18 ` Ming Lei
2023-12-04 13:13 ` John Garry
2023-12-05 1:45 ` Ming Lei [this message]
2023-12-05 10:49 ` John Garry
2023-09-29 10:27 ` [PATCH 11/21] fs: xfs: Don't use low-space allocator for alignment > 1 John Garry
2023-10-03 1:16 ` Dave Chinner
2023-10-03 3:00 ` Darrick J. Wong
2023-10-03 4:34 ` Dave Chinner
2023-10-03 10:22 ` John Garry
2023-09-29 10:27 ` [PATCH 12/21] fs: xfs: Introduce FORCEALIGN inode flag John Garry
2023-11-09 15:24 ` Christoph Hellwig
2023-09-29 10:27 ` [PATCH 13/21] fs: xfs: Make file data allocations observe the 'forcealign' flag John Garry
2023-10-03 1:42 ` Dave Chinner
2023-10-03 10:13 ` John Garry
2023-09-29 10:27 ` [PATCH 14/21] fs: xfs: Enable file data forcealign feature John Garry
2023-09-29 10:27 ` [PATCH 15/21] fs: xfs: Support atomic write for statx John Garry
2023-10-03 3:32 ` Dave Chinner
2023-10-03 10:56 ` John Garry
2023-10-03 16:10 ` Darrick J. Wong
2023-09-29 10:27 ` [PATCH 16/21] fs: iomap: Atomic write support John Garry
2023-10-03 4:24 ` Dave Chinner
2023-10-03 12:55 ` John Garry
2023-10-03 16:47 ` Darrick J. Wong
2023-10-04 1:16 ` Dave Chinner
2023-10-24 12:59 ` John Garry
2023-09-29 10:27 ` [PATCH 17/21] fs: xfs: iomap atomic " John Garry
2023-11-09 15:26 ` Christoph Hellwig
2023-11-10 10:42 ` John Garry
2023-11-28 8:56 ` John Garry
2023-11-28 13:56 ` Christoph Hellwig
2023-11-28 17:42 ` John Garry
2023-11-29 2:45 ` Martin K. Petersen
2023-12-04 13:45 ` Christoph Hellwig
2023-12-04 15:19 ` John Garry
2023-12-04 15:39 ` Christoph Hellwig
2023-12-04 18:06 ` John Garry
2023-12-05 4:55 ` Theodore Ts'o
2023-12-05 11:09 ` John Garry
2023-12-05 13:59 ` Ming Lei
2023-09-29 10:27 ` [PATCH 18/21] scsi: sd: Support reading atomic properties from block limits VPD John Garry
2023-09-29 17:54 ` Bart Van Assche
2023-10-02 11:27 ` John Garry
2023-10-06 17:52 ` Bart Van Assche
2023-10-06 23:48 ` Martin K. Petersen
2023-09-29 10:27 ` [PATCH 19/21] scsi: sd: Add WRITE_ATOMIC_16 support John Garry
2023-09-29 17:59 ` Bart Van Assche
2023-10-02 11:36 ` John Garry
2023-10-02 19:21 ` Bart Van Assche
2023-09-29 10:27 ` [PATCH 20/21] scsi: scsi_debug: Atomic write support John Garry
2023-09-29 10:27 ` [PATCH 21/21] nvme: Support atomic writes John Garry
[not found] ` <CGME20231004113943eucas1p23a51ce5ef06c36459f826101bb7b85fc@eucas1p2.samsung.com>
2023-10-04 11:39 ` Pankaj Raghav
2023-10-05 10:24 ` John Garry
2023-10-05 13:32 ` Pankaj Raghav
2023-10-05 15:05 ` John Garry
2023-11-09 15:36 ` Christoph Hellwig
2023-11-09 15:42 ` Matthew Wilcox
2023-11-09 15:46 ` Christoph Hellwig
2023-11-09 19:08 ` John Garry
2023-11-10 6:29 ` Christoph Hellwig
2023-11-10 8:44 ` John Garry
2023-09-29 14:58 ` [PATCH 00/21] block " Bart Van Assche
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