From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>, Ted Ts'o <tytso@mit.edu>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?
Date: Tue, 22 Jun 2021 19:04:02 +0100 [thread overview]
Message-ID: <YNImEkqizzuStW72@casper.infradead.org> (raw)
In-Reply-To: <3231150.1624384533@warthog.procyon.org.uk>
On Tue, Jun 22, 2021 at 06:55:33PM +0100, David Howells wrote:
> 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.
Huh? Last I checked, the fault_in_readable actually read a byte from
the page. It has to wait for the read to complete before that can
happen.
next prev parent reply other threads:[~2021-06-22 18:09 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 15:20 Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"? David Howells
2021-06-22 15:27 ` Al Viro
2021-06-22 15:36 ` Al Viro
2021-06-22 17:25 ` Matthew Wilcox
2021-06-22 17:39 ` Linus Torvalds
2021-06-22 17:55 ` David Howells
2021-06-22 18:04 ` Matthew Wilcox [this message]
2021-06-22 18:07 ` Linus Torvalds
2021-06-22 18:16 ` Nadav Amit
2021-06-22 18:23 ` Matthew Wilcox
2021-06-22 18:28 ` Linus Torvalds
2021-06-22 18:36 ` Matthew Wilcox
2021-06-22 18:51 ` Nadav Amit
2021-06-22 18:57 ` Linus Torvalds
2021-06-22 18:23 ` David Howells
2021-06-22 18:32 ` Linus Torvalds
2021-06-22 18:13 ` David Howells
2021-06-22 15:32 ` Linus Torvalds
2021-06-22 15:53 ` Linus Torvalds
2021-06-22 15:32 ` Matthew Wilcox
2021-06-22 16:27 ` David Howells
2021-06-22 21:55 ` David Laight
2021-06-22 22:04 ` Matthew Wilcox
2021-06-22 22:31 ` David Laight
2021-06-22 22:20 ` Dave Chinner
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