From: John Garry <john.g.garry@oracle.com>
To: Ming Lei <ming.lei@redhat.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 10:49:49 +0000 [thread overview]
Message-ID: <c8ef6c57-5e3a-4c12-9f0f-a2e1b1e49ddc@oracle.com> (raw)
In-Reply-To: <ZW6A0R04Gk/04EHj@fedora>
On 05/12/2023 01:45, Ming Lei wrote:
>> 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?
About atomic boundary, we just don't allow a merge which will result in
a write which will straddle a boundary as there are no guarantees of
atomicity then.
Having said this, atomic write boundary is just relevant to NVMe, so if
we don't have merges there, then we could just omit this code.
>
>>> 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,
Correct
> 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?
Actually if WRITE > boundary then we must be crossing a boundary and
should return true, which is what the first condition checks.
However 2x naturally-aligned atomic writes could be less than
atomic_write_max_bytes but still straddle if merged.
> 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.
On a related topic, as I understand, for NVMe we just split bios
according to virt boundary for PRP, but we won't always use PRP. So is
there value in not splitting bio according to PRP if SGL will actually
be used?
>
>> 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?
My concern is that we don't enforce that, so we may issue atomic writes
which exceed max_sectors_kb.
If we did enforce it, then atomic_write_unit_min_bytes,
atomic_write_unit_max_bytes, and atomic_write_max_bytes all need to be
limited according to max_sectors_kb.
Thanks,
John
next prev parent reply other threads:[~2023-12-05 10:50 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
2023-12-05 10:49 ` John Garry [this message]
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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