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Date:   Sat, 25 Nov 2017 22:35:43 +0000
From:   David Howells <>
To:     Linus Torvalds <>
        linux-fsdevel <>,
        Linux Kernel Mailing List <>
Subject: Re: [GIT PULL] afs: Fixes

Linus Torvalds <> wrote:

> So I see in the commit message why afs needs to do this, but it's
> worth pointing out that it's
>  (a) impossible to avoid the "inconsistent data" case for writable mmap'ed
>  pages

Doesn't clear_page_dirty_for_io() write-protect the PTE for the page to be
written out, in which case ->page_mkwrite() will get called again before the
page is redirtied?

>  (b) can cause some really nasty latency issues

True, but I think the most common case is a file being opened, written start
to finish and then closed.  Actually, the worst-handled thing I've seen is a
shell script appending a bunch of things to a file because ->flush() syncs the
file each time it is closed:-/

What would you recommend instead?  I'm currently trying and keep track of what
needs to be written so that I only write what's changed to the server, rather
than writing only whole pages.


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