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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	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 11:57:10 -0700	[thread overview]
Message-ID: <CAHk-=whDyrOMJMZBxtTUaMeuSd_dafiR_DFCwsLSbJuLwEuYsw@mail.gmail.com> (raw)
In-Reply-To: <F78E1A78-DB7E-4F3A-8C7C-842AA757E4FE@gmail.com>

On Tue, Jun 22, 2021 at 11:51 AM Nadav Amit <nadav.amit@gmail.com> wrote:
> Just reminding the alternative (in the RFC that I mentioned before):
> a vDSO exception table entry for a memory accessing function in the
> vDSO. It then behaves as a sort of MADV_WILLNEED for the faulting
> page if an exception is triggered. Unlike MADV_WILLNEED it maps the
> page if no IO is needed. It can return through a register whether
> the page was present or not.

Yeah, that looks like a user-space equivalent.

And thanks to the vdso, it doesn't need to support all architectures.
Unlike a kernel model would (but yes, a kernel model could then have a
fallback for the non-prefetching synchronous case instead, so I guess
we could just do one architecture at a time).

               Linus

  reply	other threads:[~2021-06-22 18:57 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
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 [this message]
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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