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Date:   Tue, 22 Jun 2021 18:55:33 +0100
From:   David Howells <>
To:     Linus Torvalds <>
Cc:, Matthew Wilcox <>,
        Al Viro <>, "Ted Ts'o" <>,
        Dave Hansen <>,
        Andrew Morton <>,
        Linux-MM <>,
        Ext4 Developers List <>,
        linux-fsdevel <>,
        Linux Kernel Mailing List <>
Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?

Linus Torvalds <> wrote:

> End result: doing the fault_in_readable "unnecessarily" at the
> beginning is likely the better optimization. It's basically free when
> it's not necessary, and it avoids an extra fault (and extra
> lock/unlock and retry) when it does end up faulting pages in.

It may also cause the read in to happen in the background whilst write_begin
is being done.


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