linux-ext4 - Re: Do we need to unrevert "fs: do not prefault sys

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Message-ID: <3232238.1624385582@warthog.procyon.org.uk>
Date:   Tue, 22 Jun 2021 19:13:02 +0100
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>, Ted Ts'o <tytso@....edu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?

Matthew Wilcox <willy@...radead.org> wrote:

> > 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.

Ah, good point.

David