From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754524Ab2DPM1F (ORCPT ); Mon, 16 Apr 2012 08:27:05 -0400 Received: from cantor2.suse.de ([195.135.220.15]:47724 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753610Ab2DPMRM (ORCPT ); Mon, 16 Apr 2012 08:17:12 -0400 From: Mel Gorman To: Andrew Morton Cc: Linux-MM , Linux-Netdev , LKML , David Miller , Neil Brown , Peter Zijlstra , Mike Christie , Eric B Munson , Mel Gorman Subject: [PATCH 05/16] mm: allow PF_MEMALLOC from softirq context Date: Mon, 16 Apr 2012 13:16:52 +0100 Message-Id: <1334578624-23257-6-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.7.9.2 In-Reply-To: <1334578624-23257-1-git-send-email-mgorman@suse.de> References: <1334578624-23257-1-git-send-email-mgorman@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is needed to allow network softirq packet processing to make use of PF_MEMALLOC. Currently softirq context cannot use PF_MEMALLOC due to it not being associated with a task, and therefore not having task flags to fiddle with - thus the gfp to alloc flag mapping ignores the task flags when in interrupts (hard or soft) context. Allowing softirqs to make use of PF_MEMALLOC therefore requires some trickery. We basically borrow the task flags from whatever process happens to be preempted by the softirq. So we modify the gfp to alloc flags mapping to not exclude task flags in softirq context, and modify the softirq code to save, clear and restore the PF_MEMALLOC flag. The save and clear, ensures the preempted task's PF_MEMALLOC flag doesn't leak into the softirq. The restore ensures a softirq's PF_MEMALLOC flag cannot leak back into the preempted process. Signed-off-by: Peter Zijlstra Signed-off-by: Mel Gorman --- include/linux/sched.h | 7 +++++++ kernel/softirq.c | 3 +++ mm/page_alloc.c | 6 +++++- 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 81a173c..2ad408f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1913,6 +1913,13 @@ static inline void rcu_copy_process(struct task_struct *p) #endif +static inline void tsk_restore_flags(struct task_struct *p, + unsigned long pflags, unsigned long mask) +{ + p->flags &= ~mask; + p->flags |= pflags & mask; +} + #ifdef CONFIG_SMP extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask); diff --git a/kernel/softirq.c b/kernel/softirq.c index 671f959..d349caa 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -210,6 +210,8 @@ asmlinkage void __do_softirq(void) __u32 pending; int max_restart = MAX_SOFTIRQ_RESTART; int cpu; + unsigned long pflags = current->flags; + current->flags &= ~PF_MEMALLOC; pending = local_softirq_pending(); account_system_vtime(current); @@ -265,6 +267,7 @@ restart: account_system_vtime(current); __local_bh_enable(SOFTIRQ_OFFSET); + tsk_restore_flags(current, pflags, PF_MEMALLOC); } #ifndef __ARCH_HAS_DO_SOFTIRQ diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ee9f49c..15c0ff7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2211,7 +2211,11 @@ gfp_to_alloc_flags(gfp_t gfp_mask) if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { if (gfp_mask & __GFP_MEMALLOC) alloc_flags |= ALLOC_NO_WATERMARKS; - else if (likely(!(gfp_mask & __GFP_NOMEMALLOC)) && !in_interrupt()) + else if (in_serving_softirq() && (current->flags & PF_MEMALLOC)) + alloc_flags |= ALLOC_NO_WATERMARKS; + else if (!in_interrupt() && + ((current->flags & PF_MEMALLOC) || + unlikely(test_thread_flag(TIF_MEMDIE)))) alloc_flags |= ALLOC_NO_WATERMARKS; } -- 1.7.9.2