Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760259Ab2EIQlJ (ORCPT ); Wed, 9 May 2012 12:41:09 -0400 Received: from na3sys009aog118.obsmtp.com ([74.125.149.244]:45216 "HELO na3sys009aog118.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756989Ab2EIQlH (ORCPT ); Wed, 9 May 2012 12:41:07 -0400 MIME-Version: 1.0 In-Reply-To: References: <1336503339-18722-1-git-send-email-pshelar@nicira.com> <1336504276.3752.2600.camel@edumazet-glaptop> Date: Wed, 9 May 2012 09:41:05 -0700 Message-ID: Subject: Re: [PATCH] mm: sl[auo]b: Use atomic bit operations to update page-flags. From: Pravin Shelar To: Christoph Lameter Cc: Eric Dumazet , penberg@kernel.org, mpm@selenic.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jesse@nicira.com, abhide@nicira.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1395 Lines: 29 On Tue, May 8, 2012 at 12:22 PM, Christoph Lameter wrote: > On Tue, 8 May 2012, Eric Dumazet wrote: > >> On Tue, 2012-05-08 at 11:55 -0700, Pravin B Shelar wrote: >> > Transparent huge pages can change page->flags (PG_compound_lock) >> > without taking Slab lock. So sl[auo]b need to use atomic bit >> > operation while changing page->flags. >> > Specificly this patch fixes race between compound_unlock and slab >> > functions which does page-flags update. This can occur when >> > get_page/put_page is called on page from slab object. >> >> >> But should get_page()/put_page() be called on a page own by slub ? > > Can occur in slab allocators if the slab memory is used for DMA. I dont > like the performance impact of the atomics. In particular slab_unlock() in > slub is or used to be a hot path item. It is still hot on arches that do > not support this_cpu_cmpxchg_double. With the cmpxchg_double only the > debug mode is affected. > I agree this would impact performance. I am not sure how else we can fix this issue. As far as slab_unlock in hot path case is concerned, it is more likely to corrupt page->flags in that case. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/