From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754560Ab1LVAqf (ORCPT ); Wed, 21 Dec 2011 19:46:35 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:59028 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752890Ab1LVAqe (ORCPT ); Wed, 21 Dec 2011 19:46:34 -0500 Date: Wed, 21 Dec 2011 16:46:29 -0800 From: Tejun Heo To: Andrew Morton Cc: Linus Torvalds , linux-kernel@vger.kernel.org Subject: [PATCH UPDATED 2/2] mempool: fix first round failure behavior Message-ID: <20111222004629.GO9213@google.com> References: <20111222001800.GL9213@google.com> <20111222001939.GM9213@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111222001939.GM9213@google.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org mempool modifies gfp_mask so that the backing allocator doesn't try too hard or trigger warning message when there's pool to fall back on. In addition, for the first try, it removes __GFP_WAIT and IO, so that it doesn't trigger reclaim or wait when allocation can be fulfilled from pool; however, when that allocation fails and pool is empty too, it waits for the pool to be replenished before retrying. Allocation which could have succeeded after a bit of reclaim has to wait on the reserved items and it's not like mempool doesn't retry with __GFP_WAIT and IO. It just does that *after* someone returns an element, pointlessly delaying things. Fix it by retrying immediately if the first round of allocation attempts w/o __GFP_WAIT and IO fails. Signed-off-by: Tejun Heo Cc: Andrew Morton --- The code hasn't changed. Only the description and comment are updated. It doesn't affect anything regarding emergency pool. It just changes when the first retry happens. That said, I still find it a bit unsettling that a GFP_ATOMIC allocation which would otherwise succeed may fail when issued through mempool. Maybe the RTTD is clearing __GFP_NOMEMALLOC on retry if the gfp requsted by the caller is !__GFP_WAIT && !__GFP_NOMEMALLOC? Thanks. mm/mempool.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) Index: work/mm/mempool.c =================================================================== --- work.orig/mm/mempool.c +++ work/mm/mempool.c @@ -221,14 +221,23 @@ repeat_alloc: return element; } - /* We must not sleep in the GFP_ATOMIC case */ + /* + * We use gfp mask w/o __GFP_WAIT or IO for the first round. If + * alloc failed with that and @pool was empty, retry immediately. + */ + if (gfp_temp != gfp_mask) { + gfp_temp = gfp_mask; + spin_unlock_irqrestore(&pool->lock, flags); + goto repeat_alloc; + } + + /* We must not sleep if !__GFP_WAIT */ if (!(gfp_mask & __GFP_WAIT)) { spin_unlock_irqrestore(&pool->lock, flags); return NULL; } /* Let's wait for someone else to return an element to @pool */ - gfp_temp = gfp_mask; init_wait(&wait); prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);