From: Junio C Hamano <gitster@pobox.com>
To: Christoph Hellwig <hch@lst.de>
Cc: "Jeff King" <peff@peff.net>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
git@vger.kernel.org, tytso@mit.edu,
"Linus Torvalds" <torvalds@linux-foundation.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH 1/2] sha1-file: fsync() loose dir entry when core.fsyncObjectFiles
Date: Thu, 17 Sep 2020 08:37:19 -0700 [thread overview]
Message-ID: <xmqqzh5os9cg.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20200917145653.GA30972@lst.de> (Christoph Hellwig's message of "Thu, 17 Sep 2020 16:56:53 +0200")
Christoph Hellwig <hch@lst.de> writes:
> On Thu, Sep 17, 2020 at 10:55:23AM -0400, Jeff King wrote:
>> On Thu, Sep 17, 2020 at 04:09:12PM +0200, Christoph Hellwig wrote:
>>
>> > On Thu, Sep 17, 2020 at 01:28:29PM +0200, Ævar Arnfjörð Bjarmason wrote:
>> > > Change the behavior of core.fsyncObjectFiles to also sync the
>> > > directory entry. I don't have a case where this broke, just going by
>> > > paranoia and the fsync(2) manual page's guarantees about its behavior.
>> >
>> > It is not just paranoia, but indeed what is required from the standards
>> > POV. At least for many Linux file systems your second fsync will be
>> > very cheap (basically a NULL syscall) as the log has alredy been forced
>> > all the way by the first one, but you can't rely on that.
>>
>> Is it sufficient to fsync() just the surrounding directory? I.e., if I
>> do:
>>
>> mkdir("a");
>> mkdir("a/b");
>> open("a/b/c", O_WRONLY);
>>
>> is it enough to fsync() a descriptor pointing to "a/b", or should I
>> also do "a"?
>
> You need to fsync both to be fully compliant, even if just fsyncing b
> will work for most but not all file systems. The good news is that
> for those common file systems the extra fsync of a is almost free.
Back to Ævar's patch, when creating a new loose object, we do these
things:
1. create temporary file and write the compressed contents to it
while computing its object name
2. create the fan-out directory under .git/objects/ if needed
3. mv temporary file to its final name
and the patch adds open+fsync+close on the fan-out directory. In
the above exchange with Peff, we learned that open+fsync+close needs
to be done on .git/objects if we created the fan-out directory, too.
Am I reading the above correctly?
Thanks.
next prev parent reply other threads:[~2020-09-17 15:43 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 18:48 [PATCH] enable core.fsyncObjectFiles by default Christoph Hellwig
2018-01-17 19:04 ` Junio C Hamano
2018-01-17 19:35 ` Christoph Hellwig
2018-01-17 20:05 ` Andreas Schwab
2018-01-17 19:37 ` Matthew Wilcox
2018-01-17 19:42 ` Christoph Hellwig
2018-01-17 21:44 ` Ævar Arnfjörð Bjarmason
2018-01-17 22:07 ` Linus Torvalds
2018-01-17 22:25 ` Linus Torvalds
2018-01-17 23:16 ` Ævar Arnfjörð Bjarmason
2018-01-17 23:42 ` Linus Torvalds
2018-01-17 23:52 ` Theodore Ts'o
2018-01-17 23:57 ` Linus Torvalds
2018-01-18 16:27 ` Christoph Hellwig
2018-01-19 19:08 ` Junio C Hamano
2018-01-20 22:14 ` Theodore Ts'o
2018-01-20 22:27 ` Junio C Hamano
2018-01-22 15:09 ` Ævar Arnfjörð Bjarmason
2018-01-22 18:09 ` Theodore Ts'o
2018-01-23 0:47 ` Jeff King
2018-01-23 5:45 ` Theodore Ts'o
2018-01-23 16:17 ` Jeff King
2018-01-23 0:25 ` Jeff King
2018-01-21 21:32 ` Chris Mason
2020-09-17 11:06 ` Ævar Arnfjörð Bjarmason
2020-09-17 11:28 ` [RFC PATCH 0/2] should core.fsyncObjectFiles fsync the dir entry + docs Ævar Arnfjörð Bjarmason
2020-09-17 11:28 ` [RFC PATCH 1/2] sha1-file: fsync() loose dir entry when core.fsyncObjectFiles Ævar Arnfjörð Bjarmason
2020-09-17 13:16 ` Jeff King
2020-09-17 15:09 ` Christoph Hellwig
2020-09-17 14:09 ` Christoph Hellwig
2020-09-17 14:55 ` Jeff King
2020-09-17 14:56 ` Christoph Hellwig
2020-09-17 15:37 ` Junio C Hamano [this message]
2020-09-17 17:12 ` Jeff King
2020-09-17 20:37 ` Taylor Blau
2020-09-22 10:42 ` Ævar Arnfjörð Bjarmason
2020-09-17 20:21 ` Johannes Sixt
2020-09-22 8:24 ` Ævar Arnfjörð Bjarmason
2020-11-19 11:38 ` Johannes Schindelin
2020-09-17 11:28 ` [RFC PATCH 2/2] core.fsyncObjectFiles: make the docs less flippant Ævar Arnfjörð Bjarmason
2020-09-17 14:12 ` Christoph Hellwig
2020-09-17 15:43 ` Junio C Hamano
2020-09-17 20:15 ` Johannes Sixt
2020-10-08 8:13 ` Johannes Schindelin
2020-10-08 15:57 ` Ævar Arnfjörð Bjarmason
2020-10-08 18:53 ` Junio C Hamano
2020-10-09 10:44 ` Johannes Schindelin
2020-09-17 19:21 ` Marc Branchaud
2020-09-17 14:14 ` [PATCH] enable core.fsyncObjectFiles by default Christoph Hellwig
2020-09-17 15:30 ` Junio C Hamano
2018-01-17 20:55 ` Jeff King
2018-01-17 21:10 ` Christoph Hellwig
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