From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758274Ab3FCOxF (ORCPT ); Mon, 3 Jun 2013 10:53:05 -0400 Received: from www.sr71.net ([198.145.64.142]:57588 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753768Ab3FCOxE (ORCPT ); Mon, 3 Jun 2013 10:53:04 -0400 Message-ID: <51ACADCD.70904@sr71.net> Date: Mon, 03 Jun 2013 07:53:01 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Minchan Kim CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mgorman@suse.de, tim.c.chen@linux.intel.com Subject: Re: [v4][PATCH 1/6] mm: swap: defer clearing of page_private() for swap cache pages References: <20130531183855.44DDF928@viggo.jf.intel.com> <20130531183856.1D7D75AD@viggo.jf.intel.com> <20130603054048.GA27858@blaptop> In-Reply-To: <20130603054048.GA27858@blaptop> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/02/2013 10:40 PM, Minchan Kim wrote: >> > diff -puN mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private mm/vmscan.c >> > --- linux.git/mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private 2013-05-30 16:07:50.632079492 -0700 >> > +++ linux.git-davehans/mm/vmscan.c 2013-05-30 16:07:50.637079712 -0700 >> > @@ -494,6 +494,8 @@ static int __remove_mapping(struct addre >> > __delete_from_swap_cache(page); >> > spin_unlock_irq(&mapping->tree_lock); >> > swapcache_free(swap, page); >> > + set_page_private(page, 0); >> > + ClearPageSwapCache(page); > It it worth to support non-atomic version of ClearPageSwapCache? Just for this, probably not. It does look like a site where it would be theoretically safe to use non-atomic flag operations since the page is on a one-way trip to the allocator at this point and the __clear_page_locked() now happens _just_ after this code. But, personally, I'm happy to leave it as-is. The atomic vs. non-atomic flags look to me like a micro-optimization that we should use when we _know_ there will be some tangible benefit. Otherwise, they're just something extra for developers to trip over and cause very subtle bugs.