From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755438Ab1LVQuJ (ORCPT ); Thu, 22 Dec 2011 11:50:09 -0500 Received: from mail-gy0-f174.google.com ([209.85.160.174]:60556 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752344Ab1LVQuF (ORCPT ); Thu, 22 Dec 2011 11:50:05 -0500 Date: Thu, 22 Dec 2011 08:49:58 -0800 From: Tejun Heo To: Oleg Nesterov Cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: + mempool-fix-first-round-failure-behavior.patch added to -mm tree Message-ID: <20111222164958.GG17084@google.com> References: <20111222163900.GA1448@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111222163900.GA1448@redhat.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 Hello, Oleg. On Thu, Dec 22, 2011 at 05:39:00PM +0100, Oleg Nesterov wrote: > I can't even explain why this (simple!) logic looks confusing to me, Yeah, gfp_mask and temp confused me pretty good too. > with or without the patch. A couple of questions: > > 1. Why do we remove __GFP_WAIT unconditionally before the the > very 1st allocation? To avoid blocking when there's pool sitting around. > 2. Why do we always restore it after io_schedule(), even if > we have the reserved items? No idea. > @@ -212,10 +212,12 @@ void * mempool_alloc(mempool_t *pool, gf > gfp_mask |= __GFP_NORETRY; /* don't loop in __alloc_pages */ > gfp_mask |= __GFP_NOWARN; /* failures are OK */ > > - gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO); > - > repeat_alloc: > > + gfp_temp = gfp_mask; > + if (pool->curr_nr) > + gfp_temp &= ~(__GFP_WAIT|__GFP_IO); > + > element = pool->alloc(gfp_temp, pool->pool_data); > if (likely(element != NULL)) > return element; > @@ -229,13 +231,15 @@ repeat_alloc: > } > > /* We must not sleep in the GFP_ATOMIC case */ > - if (!(gfp_mask & __GFP_WAIT)) { > + if (!(gfp_temp & __GFP_WAIT)) { > spin_unlock_irqrestore(&pool->lock, flags); > + /* raced with another mempool_alloc? */ > + if (gfp_mask & __GFP_WAIT) > + goto repeat_alloc; > 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); Yeah, this one definitely looks better & makes more sense. Andrew, please feel free to drop mine and take this one. Thanks. -- tejun