From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756586Ab1EQTcA (ORCPT ); Tue, 17 May 2011 15:32:00 -0400 Received: from smtp-out.google.com ([74.125.121.67]:44094 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756562Ab1EQTb6 (ORCPT ); Tue, 17 May 2011 15:31:58 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=eBdXF/zXOHWVOUeMqu2lnwDk0ldYwZxEKo2+5b16RrvPtBJzUmfxjR5jbCL615wX2O URb4pjDThv4VzxAsLHOw== Date: Tue, 17 May 2011 12:31:52 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Mel Gorman cc: Andrew Morton , James Bottomley , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Christoph Lameter , Pekka Enberg , Rik van Riel , Johannes Weiner , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 Subject: Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations In-Reply-To: <20110517084227.GI5279@suse.de> Message-ID: References: <1305295404-12129-1-git-send-email-mgorman@suse.de> <1305295404-12129-4-git-send-email-mgorman@suse.de> <20110517084227.GI5279@suse.de> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 May 2011, Mel Gorman wrote: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > index 9f8a97b..057f1e2 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > > { > > > int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET; > > > const gfp_t wait = gfp_mask & __GFP_WAIT; > > > + const gfp_t can_wake_kswapd = !(gfp_mask & __GFP_NO_KSWAPD); > > > > > > /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */ > > > BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH); > > > @@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > > */ > > > alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH); > > > > > > - if (!wait) { > > > + if (!wait && can_wake_kswapd) { > > > /* > > > * Not worth trying to allocate harder for > > > * __GFP_NOMEMALLOC even if it can't schedule. > > > diff --git a/mm/slub.c b/mm/slub.c > > > index 98c358d..c5797ab 100644 > > > --- a/mm/slub.c > > > +++ b/mm/slub.c > > > @@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > > > * Let the initial higher-order allocation fail under memory pressure > > > * so we fall-back to the minimum order allocation. > > > */ > > > - alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL; > > > + alloc_gfp = (flags | __GFP_NOWARN | __GFP_NO_KSWAPD) & > > > + ~(__GFP_NOFAIL | __GFP_WAIT | __GFP_REPEAT); > > > > > > page = alloc_slab_page(alloc_gfp, node, oo); > > > if (unlikely(!page)) { > > > > It's unnecessary to clear __GFP_REPEAT, these !__GFP_NOFAIL allocations > > will immediately fail. > > > > We can enter enter direct compaction or direct reclaim > at least once. If compaction is enabled and we enter > reclaim/compaction, the presense of __GFP_REPEAT makes a difference > in should_continue_reclaim(). With compaction disabled, the presense > of the flag is relevant in should_alloc_retry() with it being possible > to loop in the allocator instead of failing the SLUB allocation and > dropping back. > You've cleared __GFP_WAIT, so it cannot enter direct compaction or direct reclaim, so clearing __GFP_REPEAT here doesn't actually do anything. That's why I suggested adding a comment about why you're clearing __GFP_WAIT: to make it obvious that these allocations will immediately fail if the alloc is unsuccessful and we don't need to add __GFP_NORETRY or remove __GFP_REPEAT. > Maybe you meant !__GFP_WAIT instead of !__GFP_NOFAIL which makes > more sense. No, I meant !__GFP_NOFAIL since the high priority allocations (if PF_MEMALLOC or TIF_MEMDIE) will not loop forever looking for a page without that bit. That allows this !__GFP_WAIT allocation to immediately fail. __GFP_NORETRY and __GFP_REPEAT are no-ops unless you have __GFP_WAIT. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta12.messagelabs.com (mail6.bemta12.messagelabs.com [216.82.250.247]) by kanga.kvack.org (Postfix) with ESMTP id D86316B0022 for ; Tue, 17 May 2011 15:31:59 -0400 (EDT) Received: from hpaq11.eem.corp.google.com (hpaq11.eem.corp.google.com [172.25.149.11]) by smtp-out.google.com with ESMTP id p4HJVt9f006208 for ; Tue, 17 May 2011 12:31:55 -0700 Received: from pxi9 (pxi9.prod.google.com [10.243.27.9]) by hpaq11.eem.corp.google.com with ESMTP id p4HJVKvL004434 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Tue, 17 May 2011 12:31:54 -0700 Received: by pxi9 with SMTP id 9so592641pxi.0 for ; Tue, 17 May 2011 12:31:54 -0700 (PDT) Date: Tue, 17 May 2011 12:31:52 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations In-Reply-To: <20110517084227.GI5279@suse.de> Message-ID: References: <1305295404-12129-1-git-send-email-mgorman@suse.de> <1305295404-12129-4-git-send-email-mgorman@suse.de> <20110517084227.GI5279@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , James Bottomley , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Christoph Lameter , Pekka Enberg , Rik van Riel , Johannes Weiner , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 On Tue, 17 May 2011, Mel Gorman wrote: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > index 9f8a97b..057f1e2 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > > { > > > int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET; > > > const gfp_t wait = gfp_mask & __GFP_WAIT; > > > + const gfp_t can_wake_kswapd = !(gfp_mask & __GFP_NO_KSWAPD); > > > > > > /* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */ > > > BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH); > > > @@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > > */ > > > alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH); > > > > > > - if (!wait) { > > > + if (!wait && can_wake_kswapd) { > > > /* > > > * Not worth trying to allocate harder for > > > * __GFP_NOMEMALLOC even if it can't schedule. > > > diff --git a/mm/slub.c b/mm/slub.c > > > index 98c358d..c5797ab 100644 > > > --- a/mm/slub.c > > > +++ b/mm/slub.c > > > @@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > > > * Let the initial higher-order allocation fail under memory pressure > > > * so we fall-back to the minimum order allocation. > > > */ > > > - alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL; > > > + alloc_gfp = (flags | __GFP_NOWARN | __GFP_NO_KSWAPD) & > > > + ~(__GFP_NOFAIL | __GFP_WAIT | __GFP_REPEAT); > > > > > > page = alloc_slab_page(alloc_gfp, node, oo); > > > if (unlikely(!page)) { > > > > It's unnecessary to clear __GFP_REPEAT, these !__GFP_NOFAIL allocations > > will immediately fail. > > > > We can enter enter direct compaction or direct reclaim > at least once. If compaction is enabled and we enter > reclaim/compaction, the presense of __GFP_REPEAT makes a difference > in should_continue_reclaim(). With compaction disabled, the presense > of the flag is relevant in should_alloc_retry() with it being possible > to loop in the allocator instead of failing the SLUB allocation and > dropping back. > You've cleared __GFP_WAIT, so it cannot enter direct compaction or direct reclaim, so clearing __GFP_REPEAT here doesn't actually do anything. That's why I suggested adding a comment about why you're clearing __GFP_WAIT: to make it obvious that these allocations will immediately fail if the alloc is unsuccessful and we don't need to add __GFP_NORETRY or remove __GFP_REPEAT. > Maybe you meant !__GFP_WAIT instead of !__GFP_NOFAIL which makes > more sense. No, I meant !__GFP_NOFAIL since the high priority allocations (if PF_MEMALLOC or TIF_MEMDIE) will not loop forever looking for a page without that bit. That allows this !__GFP_WAIT allocation to immediately fail. __GFP_NORETRY and __GFP_REPEAT are no-ops unless you have __GFP_WAIT. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org