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From:   David Howells <dhowells@redhat.com>
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To:     Linus Torvalds <torvalds@linux-foundation.org>
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        Al Viro <viro@zeniv.linux.org.uk>, "Ted Ts'o" <tytso@mit.edu>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?
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Date:   Tue, 22 Jun 2021 18:55:33 +0100
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Linus Torvalds <torvalds@linux-foundation.org> 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.

David