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From: Christoph Hellwig <hch@lst.de>
To: Neeraj Singh <nksingh85@gmail.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Neeraj Singh via GitGitGadget" <gitgitgadget@gmail.com>,
	"Git List" <git@vger.kernel.org>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Jeff King" <peff@peff.net>,
	"Jeff Hostetler" <jeffhost@microsoft.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Neeraj Singh" <neerajsi@microsoft.com>
Subject: Re: [PATCH 2/2] core.fsyncobjectfiles: batch disk flushes
Date: Thu, 26 Aug 2021 07:50:24 +0200	[thread overview]
Message-ID: <20210826055024.GA17178@lst.de> (raw)
In-Reply-To: <CANQDOdd2FDNXnXLdm2FSmxUTk3oi+mQtiW2rf3YG7MJayrexPQ@mail.gmail.com>

On Wed, Aug 25, 2021 at 05:49:45PM -0700, Neeraj Singh wrote:
> Unfortunately my perusal of the man pages and documentation I could find doesn't
> give me this level of confidence on typical Linux filesystems. For
> instance, the notion of having to
> fsync the parent directory in order to render an inode's link findable
> eliminates a lot of the
> advantage of this change, though we could batch those and would have
> to do at most 256.
> 
> This thread is somewhat instructive, but inconclusive:
> https://lwn.net/ml/linux-fsdevel/1552418820-18102-1-git-send-email-jaya@cs.utexas.edu/.

fsync/fdatasync only guarantees consistency for the file handle they
are called on.  The first linked document mentioned an implementation
artifact that file systems with metadata logging tend to force their
log out until the last modified transaction and thus force out metadata
changes done earlier.  This won't help with actual data writes at all,
as for them the fact of writing back data will often generate new
metadata changes., and in general is not a property to rely on if you
care about data integrity.  It is nice to optimize the order of the
fsync calls for metadata only workloads, as then often the later fsync
calls on earlier modified file handles will be no-ops.

> One conclusion from reviewing that thread is that as of then,
> sync_file_ranges isn't actually enough
> to make a hard guarantee about writeout occurring. See
> https://lore.kernel.org/linux-fsdevel/20190319204330.GY26298@dastard/.
> My hope is that the Linux FS developers have rectified that shortcoming by now.

I'm not sure what shortcoming you mean.  sync_file_ranges is a system
call that only causes data writeback.  It never performs metadata write
back and thus is not an integrity operation at all.  That is also very
clearly documented in the man page.

> I think my updated version of the documentation for "= false" is
> accurate and more helpful
> from a user perspective ("up to OS policy when your data becomes durable in
> the event of an unclean shutdown").  "= true" also has a reasonable
> description, though I
> might add some verbiage indicating that this setting could be costly.

Your version is much better.  In fact it almost still too nice as in
general it will not be durable and you do end up with a corrupted
repository in that case.  Note that even for bad old ext3 that was
usually the case.

  reply	other threads:[~2021-08-26  5:50 UTC|newest]

Thread overview: 160+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25  1:51 [PATCH 0/2] [RFC] Implement a bulk-checkin option for core.fsyncObjectFiles Neeraj K. Singh via GitGitGadget
2021-08-25  1:51 ` [PATCH 1/2] object-file: use futimes rather than utime Neeraj Singh via GitGitGadget
2021-08-25 13:51   ` Johannes Schindelin
2021-08-25 22:08     ` Neeraj Singh
2021-08-25  1:51 ` [PATCH 2/2] core.fsyncobjectfiles: batch disk flushes Neeraj Singh via GitGitGadget
2021-08-25  5:38   ` Christoph Hellwig
2021-08-25 17:40     ` Neeraj Singh
2021-08-26  5:54       ` Christoph Hellwig
2021-08-25 16:11   ` Ævar Arnfjörð Bjarmason
2021-08-26  0:49     ` Neeraj Singh
2021-08-26  5:50       ` Christoph Hellwig [this message]
2021-08-28  0:20         ` Neeraj Singh
2021-08-28  6:57           ` Christoph Hellwig
2021-08-31 19:59             ` Neeraj Singh
2021-09-01  5:09               ` Christoph Hellwig
2021-08-26  5:57     ` Christoph Hellwig
2021-08-25 18:52   ` Johannes Schindelin
2021-08-25 21:26     ` Junio C Hamano
2021-08-26  1:19     ` Neeraj Singh
2021-08-25 16:58 ` [PATCH 0/2] [RFC] Implement a bulk-checkin option for core.fsyncObjectFiles Neeraj Singh
2021-08-27 23:49 ` [PATCH v2 0/6] Implement a batched fsync " Neeraj K. Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 1/6] object-file: use futimens rather than utime Neeraj Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 2/6] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 3/6] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 4/6] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 5/6] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-08-27 23:49   ` [PATCH v2 6/6] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-09-07 19:44   ` [PATCH v2 0/6] Implement a batched fsync option for core.fsyncObjectFiles Neeraj Singh
2021-09-07 19:50     ` Ævar Arnfjörð Bjarmason
2021-09-07 19:54     ` Randall S. Becker
2021-09-08  0:54       ` Neeraj Singh
2021-09-08  1:22         ` Ævar Arnfjörð Bjarmason
2021-09-08 14:04           ` Randall S. Becker
2021-09-08 19:01           ` Neeraj Singh
2021-09-08  0:55     ` Neeraj Singh
2021-09-08  6:44       ` Junio C Hamano
2021-09-08  6:49         ` Christoph Hellwig
2021-09-08 13:57           ` Randall S. Becker
2021-09-08 14:13             ` 'Christoph Hellwig'
2021-09-08 14:25               ` Randall S. Becker
2021-09-08 16:34         ` Neeraj Singh
2021-09-08 19:12           ` Junio C Hamano
2021-09-08 19:20             ` Neeraj Singh
2021-09-08 19:23           ` Ævar Arnfjörð Bjarmason
2021-09-14  3:38   ` [PATCH v3 " Neeraj K. Singh via GitGitGadget
2021-09-14  3:38     ` [PATCH v3 1/6] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-09-14  3:38     ` [PATCH v3 2/6] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-09-14 10:39       ` Bagas Sanjaya
2021-09-14 19:05         ` Neeraj Singh
2021-09-14 19:34       ` Junio C Hamano
2021-09-14 20:33         ` Junio C Hamano
2021-09-15  4:55         ` Neeraj Singh
2021-09-14  3:38     ` [PATCH v3 3/6] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-09-14  3:38     ` [PATCH v3 4/6] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-09-14 19:35       ` Junio C Hamano
2021-09-14  3:38     ` [PATCH v3 5/6] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-09-14  3:38     ` [PATCH v3 6/6] core.fsyncobjectfiles: enable batch mode for testing Neeraj Singh via GitGitGadget
2021-09-15 16:21       ` Junio C Hamano
2021-09-15 22:43         ` Neeraj Singh
2021-09-15 23:12           ` Junio C Hamano
2021-09-16  6:19             ` Junio C Hamano
2021-09-14  5:49     ` [PATCH v3 0/6] Implement a batched fsync option for core.fsyncObjectFiles Christoph Hellwig
2021-09-20 22:15     ` [PATCH v4 " Neeraj K. Singh via GitGitGadget
2021-09-20 22:15       ` [PATCH v4 1/6] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-09-20 22:15       ` [PATCH v4 2/6] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-09-21 23:16         ` Ævar Arnfjörð Bjarmason
2021-09-22  1:23           ` Neeraj Singh
2021-09-22  2:02             ` Ævar Arnfjörð Bjarmason
2021-09-22 19:46             ` Neeraj Singh
2021-09-20 22:15       ` [PATCH v4 3/6] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-09-21 23:42         ` Ævar Arnfjörð Bjarmason
2021-09-22  1:23           ` Neeraj Singh
2021-09-20 22:15       ` [PATCH v4 4/6] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-09-21 23:46         ` Ævar Arnfjörð Bjarmason
2021-09-22  1:27           ` Neeraj Singh
2021-09-23 22:32             ` Neeraj Singh
2021-09-20 22:15       ` [PATCH v4 5/6] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-09-21 23:54         ` Ævar Arnfjörð Bjarmason
2021-09-22  1:30           ` Neeraj Singh
2021-09-22  1:58             ` Ævar Arnfjörð Bjarmason
2021-09-22 17:55               ` Neeraj Singh
2021-09-22 20:01                 ` Ævar Arnfjörð Bjarmason
2021-09-20 22:15       ` [PATCH v4 6/6] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-09-24 20:12       ` [PATCH v5 0/7] Implement a batched fsync option for core.fsyncObjectFiles Neeraj K. Singh via GitGitGadget
2021-09-24 20:12         ` [PATCH v5 1/7] object-file.c: do not rename in a temp odb Neeraj Singh via GitGitGadget
2021-09-24 20:12         ` [PATCH v5 2/7] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-09-24 20:12         ` [PATCH v5 3/7] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-09-24 21:47           ` Neeraj Singh
2021-09-24 20:12         ` [PATCH v5 4/7] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-09-24 21:49           ` Neeraj Singh
2021-09-24 20:12         ` [PATCH v5 5/7] unpack-objects: " Neeraj Singh via GitGitGadget
2021-09-24 20:12         ` [PATCH v5 6/7] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-09-24 20:12         ` [PATCH v5 7/7] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-09-24 23:31         ` [PATCH v5 0/7] Implement a batched fsync option for core.fsyncObjectFiles Neeraj Singh
2021-09-24 23:53         ` [PATCH v6 0/8] " Neeraj K. Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 1/8] object-file.c: do not rename in a temp odb Neeraj Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 2/8] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 3/8] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-09-25  3:15             ` Bagas Sanjaya
2021-09-27  0:27               ` Neeraj Singh
2021-09-24 23:53           ` [PATCH v6 4/8] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-09-27 20:07             ` Junio C Hamano
2021-09-27 20:55               ` Neeraj Singh
2021-09-27 21:03                 ` Neeraj Singh
2021-09-27 23:53                   ` Junio C Hamano
2021-09-24 23:53           ` [PATCH v6 5/8] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 6/8] unpack-objects: " Neeraj Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 7/8] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-09-24 23:53           ` [PATCH v6 8/8] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-09-28 23:32           ` [PATCH v7 0/9] Implement a batched fsync option for core.fsyncObjectFiles Neeraj K. Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 1/9] object-file.c: do not rename in a temp odb Neeraj Singh via GitGitGadget
2021-09-28 23:55               ` Jeff King
2021-09-29  0:10                 ` Neeraj Singh
2021-09-28 23:32             ` [PATCH v7 2/9] tmp-objdir: new API for creating temporary writable databases Neeraj Singh via GitGitGadget
2021-09-29  8:41               ` Elijah Newren
2021-09-29 16:40                 ` Neeraj Singh
2021-09-28 23:32             ` [PATCH v7 3/9] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 4/9] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 5/9] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 6/9] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 7/9] unpack-objects: " Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 8/9] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-09-28 23:32             ` [PATCH v7 9/9] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-10-04 16:57             ` [PATCH v8 0/9] Implement a batched fsync option for core.fsyncObjectFiles Neeraj K. Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 1/9] tmp-objdir: new API for creating temporary writable databases Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 2/9] tmp-objdir: disable ref updates when replacing the primary odb Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 3/9] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 4/9] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 5/9] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 6/9] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 7/9] unpack-objects: " Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 8/9] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-10-04 16:57               ` [PATCH v8 9/9] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-11-15 23:50               ` [PATCH v9 0/9] Implement a batched fsync option for core.fsyncObjectFiles Neeraj K. Singh via GitGitGadget
2021-11-15 23:50                 ` [PATCH v9 1/9] tmp-objdir: new API for creating temporary writable databases Neeraj Singh via GitGitGadget
2021-11-30 21:27                   ` Elijah Newren
2021-11-30 21:52                     ` Neeraj Singh
2021-11-30 22:36                       ` Elijah Newren
2021-11-15 23:50                 ` [PATCH v9 2/9] tmp-objdir: disable ref updates when replacing the primary odb Neeraj Singh via GitGitGadget
2021-11-16  7:23                   ` Ævar Arnfjörð Bjarmason
2021-11-16 20:38                     ` Neeraj Singh
2021-11-15 23:50                 ` [PATCH v9 3/9] bulk-checkin: rename 'state' variable and separate 'plugged' boolean Neeraj Singh via GitGitGadget
2021-11-15 23:50                 ` [PATCH v9 4/9] core.fsyncobjectfiles: batched disk flushes Neeraj Singh via GitGitGadget
2021-11-15 23:50                 ` [PATCH v9 5/9] core.fsyncobjectfiles: add windows support for batch mode Neeraj Singh via GitGitGadget
2021-11-15 23:51                 ` [PATCH v9 6/9] update-index: use the bulk-checkin infrastructure Neeraj Singh via GitGitGadget
2021-11-15 23:51                 ` [PATCH v9 7/9] unpack-objects: " Neeraj Singh via GitGitGadget
2021-11-15 23:51                 ` [PATCH v9 8/9] core.fsyncobjectfiles: tests for batch mode Neeraj Singh via GitGitGadget
2021-11-15 23:51                 ` [PATCH v9 9/9] core.fsyncobjectfiles: performance tests for add and stash Neeraj Singh via GitGitGadget
2021-11-16  8:02                 ` [PATCH v9 0/9] Implement a batched fsync option for core.fsyncObjectFiles Ævar Arnfjörð Bjarmason
2021-11-17  7:06                   ` Neeraj Singh
2021-11-17  7:24                     ` Ævar Arnfjörð Bjarmason
2021-11-18  5:03                       ` Neeraj Singh
2021-12-01 14:15                         ` Ævar Arnfjörð Bjarmason
2022-03-09 23:02                           ` Ævar Arnfjörð Bjarmason
2022-03-10  1:16                             ` Neeraj Singh
2022-03-10 14:01                               ` Ævar Arnfjörð Bjarmason
2022-03-10 17:52                                 ` Neeraj Singh
2022-03-10 18:08                                   ` rsbecker
2022-03-10 18:43                                     ` Neeraj Singh
2022-03-10 18:48                                       ` rsbecker

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