linux-kernel - Re: [rfc][patch] mm: madvise(WILLNEED) for anonymous memory

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Message-Id: <1198162560.6821.30.camel@twins>
Date:	Thu, 20 Dec 2007 15:56:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Nick Piggin <npiggin@...e.de>,
	riel <riel@...hat.com>, Lennart Poettering <mztabzr@...inter.de>
Subject: Re: [rfc][patch] mm: madvise(WILLNEED) for anonymous memory


On Thu, 2007-12-20 at 15:47 +0100, Peter Zijlstra wrote:
> On Thu, 2007-12-20 at 14:09 +0000, Hugh Dickins wrote:

> > Interesting divergence: make_pages_present faults in writable pages
> > in a writable vma, whereas the file case's force_page_cache_readahead
> > doesn't even insert the pages into the mm.
> 
> Yeah, the find_vma and write fault thing are the reason I didn't use
> make_pages_present.
> 
> I had noticed the difference in pte population between
> force_page_cache_readahead and make_pages_present, but it seemed to me
> that writing a function to walk the page tables and populate the
> swapcache but not populate the ptes wasn't worth the effort.

Ah, another, more important difference:

force_page_cache_readahead will not wait for the read to complete,
whereas get_user_pages() will be fully synchronous.

I think I'd better come up with something else then,..

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