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Date:   Thu, 26 Aug 2021 07:57:19 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     =?iso-8859-1?Q?=C6var_Arnfj=F6r=F0?= Bjarmason <avarab@gmail.com>
Cc:     Neeraj Singh via GitGitGadget <gitgitgadget@gmail.com>,
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        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
Message-ID: <20210826055719.GB17560@lst.de>
References: <pull.1076.git.git.1629856292.gitgitgadget@gmail.com> <d1e68d4a2afc1d0ba74af64680bea09f412f21cc.1629856293.git.gitgitgadget@gmail.com> <87mtp5cwpn.fsf@evledraar.gmail.com>
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On Wed, Aug 25, 2021 at 06:11:13PM +0200, Ævar Arnfjörð Bjarmason wrote:
> 3) Re some of the musings about fsync() recently in
> https://lore.kernel.org/git/877dhs20x3.fsf@evledraar.gmail.com/; is this
> method of doing not-quite-an-fsync guaranteed by some OS's / POSIX etc,
> or is it more like the initial approach before core.fsyncObjectFiles,
> i.e. the happy-go-lucky approach described in the "[...]that orders data
> writes properly[...]" documentation you're removing.

Except for the now removed ext3 filesystem in Linux that basically turned
every fsync into syncfs, that is a file system-wide sync I've never
heard about such behavior for data writeback.  Many file systems will
sometimes or always behave like that for metadata writeback, but there
is no guarantees you could rely on for that.