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Date: Mon, 23 Apr 2001 17:53:18 +0100
To: Rik van Riel <riel@conectiva.com.br>, Ingo Molnar <mingo@elte.hu>
From: Jonathan Morton <chromi@cyberspace.org>
Subject: Re: [patch] swap-speedup-2.4.3-A1, massive swapping speedup
Cc: Linus Torvalds <torvalds@transmeta.com>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Linux Kernel List <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Marcelo Tosatti <marcelo@conectiva.com.br>,
        Szabolcs Szakacsits <szaka@f-secure.com>
Sender: linux-kernel-owner@vger.kernel.org
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>There seems to be one more reason, take a look at the function
>read_swap_cache_async() in swap_state.c, around line 240:
>
>        /*
>         * Add it to the swap cache and read its contents.
>         */
>        lock_page(new_page);
>        add_to_swap_cache(new_page, entry);
>        rw_swap_page(READ, new_page, wait);
>        return new_page;
>
>Here we add an "empty" page to the swap cache and use the
>page lock to protect people from reading this non-up-to-date
>page.

How about reversing the order of the calls - ie. add the page to the cache
only when it's been filled?  That would fix the race.

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@cyberspace.org  (not for attachments)
big-mail: chromatix@penguinpowered.com
uni-mail: j.d.morton@lancaster.ac.uk

The key to knowledge is not to rely on people to teach you it.

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