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Date:   Thu, 26 Aug 2021 07:54:39 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Neeraj Singh <nksingh85@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        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>,
        =?iso-8859-1?Q?=C6var_Arnfj=F6r=F0?= Bjarmason <avarab@gmail.com>,
        "Neeraj K. Singh" <neerajsi@microsoft.com>
Subject: Re: [PATCH 2/2] core.fsyncobjectfiles: batch disk flushes
Message-ID: <20210826055439.GA17560@lst.de>
References: <pull.1076.git.git.1629856292.gitgitgadget@gmail.com> <d1e68d4a2afc1d0ba74af64680bea09f412f21cc.1629856293.git.gitgitgadget@gmail.com> <20210825053839.GA27037@lst.de> <CANQDOdf7rMyT4Swriw9=Ei7KN1iLv_dGDWSSck22Zu6AztOyjg@mail.gmail.com>
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On Wed, Aug 25, 2021 at 10:40:53AM -0700, Neeraj Singh wrote:
> I'd expect syncfs to suffer from the noisy-neighbor problem that Linus
> alluded to on the big
> thread you kicked off.

It does.  That being said I suspect in most developer workstation
use cases it will still be a win.  Maybe I'll look into implemeting
it after your series lands.

> If someone adds a more targeted bulk sync interface to the Linux
> kernel, I'm sure Git could be
> changed to use it. Maybe an fcntl(2) interface that initiates
> writeback and registers completion with an
> eventfd.

That is in general very hard to do with how the VM-level writeback
occurs.  In the file system itself it could work much better, e.g.
for XFS we write the log up to a specific sequence number and could
notify when doing that.