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Subject[PATCH 05/28] mm: allow PF_MEMALLOC from softirq context
Allow PF_MEMALLOC to be set in softirq context. When running softirqs from
a borrowed context save current->flags, ksoftirqd will have its own
task_struct.

This is needed to allow network softirq packet processing to make use of
PF_MEMALLOC.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/sched.h | 4 ++++
kernel/softirq.c | 3 +++
mm/page_alloc.c | 7 ++++---
3 files changed, 11 insertions(+), 3 deletions(-)

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -1471,9 +1471,10 @@ 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;
}

Index: linux-2.6/kernel/softirq.c
===================================================================
--- linux-2.6.orig/kernel/softirq.c
+++ linux-2.6/kernel/softirq.c
@@ -213,6 +213,8 @@ 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);
@@ -251,6 +253,7 @@ restart:

account_system_vtime(current);
_local_bh_enable();
+ tsk_restore_flags(current, pflags, PF_MEMALLOC);
}

#ifndef __ARCH_HAS_DO_SOFTIRQ
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1497,6 +1497,10 @@ static inline void put_task_struct(struc
#define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
#define used_math() tsk_used_math(current)

+#define tsk_restore_flags(p, pflags, mask) \
+ do { (p)->flags &= ~(mask); \
+ (p)->flags |= ((pflags) & (mask)); } while (0)
+
#ifdef CONFIG_SMP
extern int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask);
#else
--



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