linux-kernel - Re: Linux 2.4.34-pre3

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Message-ID: <45103D1D.20702@yahoo.com.au>
Date:	Wed, 20 Sep 2006 04:55:25 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Willy Tarreau <w@....eu>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: Linux 2.4.34-pre3

Willy Tarreau wrote:
> Hi Nick,
> 
> On Wed, Sep 20, 2006 at 03:42:06AM +1000, Nick Piggin wrote:
> 
> [cut -pre3 advertisement]
> 
> 
>>I wonder if 2.4 doesn't need the memory ordering fix to prevent pagecache
>>corruption in reclaim? (http://www.gatago.com/linux/kernel/14682626.html)
>>
>>What would need to be done is to test page_count before testing PageDirty,
>>and putting an smp_rmb between the two.
> 
> 
> I've read the thread, and Linus proposed to add an smp_wmb() in
> set_page_dirty() too.

I think that isn't needed because put_page is a RMW, which is defined
to order memory. And presumably you wouldn't set the page dirty without
a reference to the page.

> I see that an smp_rmb() is already present
> in shrink_cache() with the adequate comment.

So there is! My mistake then, I was confused and looking at
try_to_swap_out, but I see that doesn't actually free the page. Fine,
I think 2.4 is OK then.

-- 
SUSE Labs, Novell Inc.
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