linux-kernel - Re: [RFC] page fault retry with NOPAGE

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Message-Id: <20060915003529.8a59c542.akpm@osdl.org>
Date:	Fri, 15 Sep 2006 00:35:29 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-mm@...ck.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Mike Waychison <mikew@...gle.com>
Subject: Re: [RFC] page fault retry with NOPAGE_RETRY

On Fri, 15 Sep 2006 00:11:51 -0700
Andrew Morton <akpm@...l.org> wrote:

> b) It could be more efficient.  Most of the time, there's no need to
>    back all the way out of the pagefault handler and rerun the whole thing.
>    Because most of the time, nobody changed anything in the mm_struct.  We
>    _could_ just retake the mmap_sem after the page comes uptodate and, if
>    nothing has changed, proceed.  I see two ways of doing this:
> 
>    - The simple way: look to see if any other processes are sharing
>      this mm_struct.  If not, just do the synchronous read inside mmap_sem.

This assumes that no other heavyweight process will try to modify this
single-threaded process's mm.  I don't _think_ that happens anywhere, does
it?  access_process_vm() is the only case I can think of, and it does
down_read(other process's mmap_sem).

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