[PATCH -mmotm 07/30] mm: allow PF_MEMALLOC from softirq context
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From: Xiaotian Feng on 13 Jul 2010 06:30 From 32f474cffc76551ddb792454845bd473634219b5 Mon Sep 17 00:00:00 2001 From: Xiaotian Feng <dfeng(a)redhat.com> Date: Tue, 13 Jul 2010 10:41:53 +0800 Subject: [PATCH 07/30] mm: allow PF_MEMALLOC from softirq context 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 <a.p.zijlstra(a)chello.nl> Signed-off-by: Suresh Jayaraman <sjayaraman(a)suse.de> Signed-off-by: Xiaotian Feng <dfeng(a)redhat.com> --- include/linux/sched.h | 7 +++++++ kernel/softirq.c | 3 +++ mm/page_alloc.c | 7 ++++--- 3 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 1f25798..85b74b0 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1765,6 +1765,13 @@ 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 int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask); diff --git a/kernel/softirq.c b/kernel/softirq.c index 07b4f1b..0770e78 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -194,6 +194,8 @@ 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); @@ -246,6 +248,7 @@ restart: account_system_vtime(current); _local_bh_enable(); + 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 b9989c5..4b1fa10 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1928,9 +1928,10 @@ int gfp_to_alloc_flags(gfp_t gfp_mask) alloc_flags |= ALLOC_HARDER; if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { - if (!in_interrupt() && - ((p->flags & PF_MEMALLOC) || - unlikely(test_thread_flag(TIF_MEMDIE)))) + if (!in_irq() && (p->flags & PF_MEMALLOC)) + alloc_flags |= ALLOC_NO_WATERMARKS; + else if (!in_interrupt() && + unlikely(test_thread_flag(TIF_MEMDIE))) alloc_flags |= ALLOC_NO_WATERMARKS; } -- 1.7.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |