linux-kernel - Re: [PATCH] mm: PageLRU can be non-atomic bit operation

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Message-Id: <6.0.0.20.2.20070423210926.045668d0@172.19.0.2>
Date:	Mon, 23 Apr 2007 21:34:07 +0900
From:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: PageLRU can be non-atomic bit operation


 >No.  The PG_lru flag bit is just one bit amongst many others:
 >what of concurrent operations changing other bits in that same
 >unsigned long e.g. trying to lock the page by setting PG_locked?
 >There are some places where such micro-optimizations can be made
 >(typically while first allocating the page); but in general, no.

In i386 and x86_64, btsl is used to change page flag. In this case, if btsl 
without lock prefix
set PG_locked and PG_lru flag concurrently, does only one operation
succeed ?

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