Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754185Ab2HBQmN (ORCPT ); Thu, 2 Aug 2012 12:42:13 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:55171 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753099Ab2HBQmM (ORCPT ); Thu, 2 Aug 2012 12:42:12 -0400 Date: Thu, 2 Aug 2012 18:42:03 +0200 From: Johannes Weiner To: Christoph Lameter Cc: Glauber Costa , linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, David Rientjes , Pekka Enberg Subject: Re: [PATCH] slub: use free_page instead of put_page for freeing kmalloc allocation Message-ID: <20120802164203.GA30111@cmpxchg.org> References: <1343913065-14631-1-git-send-email-glommer@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1871 Lines: 46 On Thu, Aug 02, 2012 at 09:06:41AM -0500, Christoph Lameter wrote: > On Thu, 2 Aug 2012, Glauber Costa wrote: > > > diff --git a/mm/slub.c b/mm/slub.c > > index e517d43..9ca4e20 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -3453,7 +3453,7 @@ void kfree(const void *x) > > if (unlikely(!PageSlab(page))) { > > BUG_ON(!PageCompound(page)); > > kmemleak_free(x); > > - put_page(page); > > + __free_pages(page, compound_order(page)); > > Hmmm... put_page would have called put_compound_page(). which would have > called the dtor function. dtor is set to __free_pages() ok which does > mlock checks and verifies that the page is in a proper condition for > freeing. Then it calls free_one_page(). > > __free_pages() decrements the refcount and then calls __free_pages_ok(). > > So we loose the checking and the dtor stuff with this patch. Guess that is > ok? The changelog is not correct, however. People DO get pages underlying slab objects and even free the slab objects before returning the page. See recent fix: commit 5bf5f03c271907978489868a4c72aeb42b5127d2 Author: Pravin B Shelar Date: Tue May 29 15:06:49 2012 -0700 mm: fix slab->page flags corruption Transparent huge pages can change page->flags (PG_compound_lock) without taking Slab lock. Since THP can not break slab pages we can safely access compound page without taking compound lock. Specifically this patch fixes a race between compound_unlock() and slab functions which perform page-flags updates. This can occur when get_page()/put_page() is called on a page from slab. -- 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/