From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from edge04.upc.biz ([192.168.13.239]) by viefep17-int.chello.at (InterMail vM.7.08.02.00 201-2186-121-20061213) with ESMTP id <20080812102329.KLGS16026.viefep17-int.chello.at@edge04.upc.biz> for ; Tue, 12 Aug 2008 12:23:29 +0200 Subject: Re: [PATCH 05/30] mm: slb: add knowledge of reserve pages From: Peter Zijlstra In-Reply-To: <18593.22902.998611.967202@notabene.brown> References: <20080724140042.408642539@chello.nl> <20080724141529.635920366@chello.nl> <18593.8466.965002.476705@notabene.brown> <1218525750.10800.156.camel@twins> <18593.22902.998611.967202@notabene.brown> Content-Type: text/plain Date: Tue, 12 Aug 2008 12:23:27 +0200 Message-Id: <1218536607.10800.181.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Neil Brown Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, trond.myklebust@fys.uio.no, Daniel Lezcano , Pekka Enberg List-ID: On Tue, 2008-08-12 at 19:35 +1000, Neil Brown wrote: > On Tuesday August 12, a.p.zijlstra@chello.nl wrote: > > On Tue, 2008-08-12 at 15:35 +1000, Neil Brown wrote: > > > On Thursday July 24, a.p.zijlstra@chello.nl wrote: > > > > Restrict objects from reserve slabs (ALLOC_NO_WATERMARKS) to allocation > > > > contexts that are entitled to it. This is done to ensure reserve pages don't > > > > leak out and get consumed. > > > > > > This looks good (we are still missing slob though, aren't we :-( ) > > > > I actually have that now, just needs some testing.. > > Cool! > > > > > > > @@ -1526,7 +1540,7 @@ load_freelist: > > > > object = c->page->freelist; > > > > if (unlikely(!object)) > > > > goto another_slab; > > > > - if (unlikely(SLABDEBUG && PageSlubDebug(c->page))) > > > > + if (unlikely(PageSlubDebug(c->page) || c->reserve)) > > > > goto debug; > > > > > > This looks suspiciously like debugging code that you have left in. > > > Is it?? > > > > Its not, we need to force slub into the debug slow path when we have a > > reserve page, otherwise we cannot do the permission check on each > > allocation. > > I see.... a little. I'm trying to avoid understanding slub too > deeply, I don't want to use up valuable brain cell :-) :-) > Would we be justified in changing the label from 'debug:' to > 'slow_path:' or something? Could do I guess. Index: linux-2.6/mm/slub.c =================================================================== --- linux-2.6.orig/mm/slub.c +++ linux-2.6/mm/slub.c @@ -1543,7 +1543,7 @@ load_freelist: if (unlikely(!object)) goto another_slab; if (unlikely(PageSlubDebug(c->page) || c->reserve)) - goto debug; + goto slow_path; c->freelist = object[c->offset]; c->page->inuse = c->page->objects; @@ -1586,11 +1586,21 @@ grow_slab: goto load_freelist; } return NULL; -debug: + +slow_path: if (PageSlubDebug(c->page) && !alloc_debug_processing(s, c->page, object, addr)) goto another_slab; + /* + * Avoid the slub fast path in slab_alloc by not setting + * c->freelist and the fast path in slab_fere by making + * node_match() fail by setting c->node to -1. + * + * We use this for for debug checks and reserve handling, + * which needs to do permission checks on each allocation. + */ + c->page->inuse++; c->page->freelist = object[c->offset]; c->node = -1; > And if it is just c->reserve, should > we avoid the call to alloc_debug_processing? We already do: if (PageSlubDebug(c->page) && !alloc_debug_processing(s, c->page, object, addr)) goto another_slab; since in that case PageSlubDebug() will be false. -- 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