From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <440CEC93.9080508@yahoo.com.au> Date: Tue, 07 Mar 2006 13:14:43 +1100 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH] avoid atomic op on page free References: <20060307001015.GG32565@linux.intel.com> <440CE797.1010303@yahoo.com.au> <20060307015810.GK32565@linux.intel.com> In-Reply-To: <20060307015810.GK32565@linux.intel.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Benjamin LaHaise Cc: akpm@osdl.org, linux-mm@kvack.org, netdev@vger.kernel.org List-ID: Benjamin LaHaise wrote: >On Tue, Mar 07, 2006 at 12:53:27PM +1100, Nick Piggin wrote: > >>You can't do this because you can't test PageLRU like that. >> >>Have a look in the lkml archives a few months back, where I proposed >>a way to do this for __free_pages(). You can't do it for put_page. >> > >Even if we know that we are the last user of the page (the count is 1)? >Who can bump the page's count then? > > Yes. vmscan. Your page_count and PageLRU tests have no synchronisation between them, which is the problem AFAIKS. Anything can happen between them and they can probably also be executed out of order (the loads). >>BTW I have quite a large backlog of patches in -mm which should end >>up avoiding an atomic or two around these parts. >> > >That certainly looks like it will help. Not taking the spinlock >unconditionally gets rid of quite a bit of the cost. > > Cool. -- Send instant messages to your online friends http://au.messenger.yahoo.com -- 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