From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 29 Sep 2008 18:36:14 +0100 From: Andy Whitcroft Subject: Re: setup_per_zone_pages_min(): zone->lock vs. zone->lru_lock Message-ID: <20080929173607.GC14905@brain> References: <1222708257.4723.23.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1222708257.4723.23.camel@localhost.localdomain> Sender: owner-linux-mm@kvack.org Return-Path: To: Gerald Schaefer Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, KAMEZAWA Hiroyuki , Yasunori Goto , Mel Gorman , Andrew Morton List-ID: On Mon, Sep 29, 2008 at 07:10:57PM +0200, Gerald Schaefer wrote: > Hi, > > is zone->lru_lock really the right lock to take in setup_per_zone_pages_min()? > All other functions in mm/page_alloc.c take zone->lock instead, for working > with page->lru free-list or PageBuddy(). > > setup_per_zone_pages_min() eventually calls move_freepages(), which is also > manipulating the page->lru free-list and checking for PageBuddy(). Both > should be protected by zone->lock instead of zone->lru_lock, if I understood > that right, or else there could be a race with the other functions in > mm/page_alloc.c. > > We ran into a list corruption bug in free_pages_bulk() once, during memory > hotplug stress test, but cannot reproduce it easily. So I cannot verify if > using zone->lock instead of zone->lru_lock would fix it, but to me it looks > like this may be the problem. > > Any thoughts? > > BTW, I also wonder if a spin_lock_irq() would be enough, instead of > spin_lock_irqsave(), because this function should never be called from > interrupt context, right? The allocator protects it freelists using zone->lock (as we can see in rmqueue_bulk), so anything which manipulates those should also be using that lock. move_freepages() is scanning the cmap and picking up free pages directly off the free lists, it is expecting those lists to be stable; it would appear to need zone->lock. It does look like setup_per_zone_pages_min() is holding the wrong thing at first look. -apw -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org