From: Matthew Wilcox <willy@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>,
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 19:36:26 +0100 [thread overview]
Message-ID: <YNItqqZA9Y1wOnZY@casper.infradead.org> (raw)
In-Reply-To: <CAHk-=wiRumzeOn1Fk-m-FiGf+sA0dSS3YPu--KAkT8-5W5yEHA@mail.gmail.com>
On Tue, Jun 22, 2021 at 11:28:30AM -0700, Linus Torvalds wrote:
> On Tue, Jun 22, 2021 at 11:23 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > It wouldn't be _that_ bad necessarily. filemap_fault:
>
> It's not actually the mm code that is the biggest problem. We
> obviously already have readahead support.
>
> It's the *fault* side.
>
> In particular, since the fault would return without actually filling
> in the page table entry (because the page isn't ready yet, and you
> cannot expose it to other threads!), you also have to jump over the
> instruction that caused this all.
Oh, I was assuming that it'd be a function call like
get_user_pages_fast(), not an instruction that was specially marked to
be jumped over. Gag reflex diminishing now?
next prev parent reply other threads:[~2021-06-22 18:37 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 15:20 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
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 [this message]
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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