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Commit 499118e9 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm: introduce memalloc_noreclaim_{save,restore} 

The previous patch ("mm: prevent potential recursive reclaim due to
clearing PF_MEMALLOC") has shown that simply setting and clearing
PF_MEMALLOC in current->flags can result in wrongly clearing a
pre-existing PF_MEMALLOC flag and potentially lead to recursive reclaim.
Let's introduce helpers that support proper nesting by saving the
previous stat of the flag, similar to the existing memalloc_noio_* and
memalloc_nofs_* helpers.  Convert existing setting/clearing of
PF_MEMALLOC within mm to the new helpers.

There are no known issues with the converted code, but the change makes
it more robust.

Link: http://lkml.kernel.org/r/20170405074700.29871-3-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Suggested-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Chris Leech <cleech@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Lee Duncan <lduncan@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 62be1511

include/linux/sched/mm.h

+12 −0
Original line number Diff line number Diff line
@@ -191,4 +191,16 @@ static inline void memalloc_nofs_restore(unsigned int flags) 
	current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags;

}



static inline unsigned int memalloc_noreclaim_save(void)

{

	unsigned int flags = current->flags & PF_MEMALLOC;

	current->flags |= PF_MEMALLOC;

	return flags;

}



static inline void memalloc_noreclaim_restore(unsigned int flags)

{

	current->flags = (current->flags & ~PF_MEMALLOC) | flags;

}



#endif /* _LINUX_SCHED_MM_H */

mm/page_alloc.c

+6 −5
Original line number Diff line number Diff line
@@ -3283,15 +3283,15 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, 
		enum compact_priority prio, enum compact_result *compact_result)

{

	struct page *page;

	unsigned int noreclaim_flag = current->flags & PF_MEMALLOC;

	unsigned int noreclaim_flag;



	if (!order)

		return NULL;



	current->flags |= PF_MEMALLOC;

	noreclaim_flag = memalloc_noreclaim_save();

	*compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,

									prio);

	current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag;

	memalloc_noreclaim_restore(noreclaim_flag);



	if (*compact_result <= COMPACT_INACTIVE)

		return NULL;
@@ -3438,12 +3438,13 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order, 
{

	struct reclaim_state reclaim_state;

	int progress;

	unsigned int noreclaim_flag;



	cond_resched();



	/* We now go into synchronous reclaim */

	cpuset_memory_pressure_bump();

	current->flags |= PF_MEMALLOC;

	noreclaim_flag = memalloc_noreclaim_save();

	lockdep_set_current_reclaim_state(gfp_mask);

	reclaim_state.reclaimed_slab = 0;

	current->reclaim_state = &reclaim_state;
@@ -3453,7 +3454,7 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order, 


	current->reclaim_state = NULL;

	lockdep_clear_current_reclaim_state();

	current->flags &= ~PF_MEMALLOC;

	memalloc_noreclaim_restore(noreclaim_flag);



	cond_resched();

mm/vmscan.c

+11 −6
Original line number Diff line number Diff line
@@ -3036,6 +3036,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, 
	struct zonelist *zonelist;

	unsigned long nr_reclaimed;

	int nid;

	unsigned int noreclaim_flag;

	struct scan_control sc = {

		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),

		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
@@ -3062,9 +3063,9 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, 
					    sc.gfp_mask,

					    sc.reclaim_idx);



	current->flags |= PF_MEMALLOC;

	noreclaim_flag = memalloc_noreclaim_save();

	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);

	current->flags &= ~PF_MEMALLOC;

	memalloc_noreclaim_restore(noreclaim_flag);



	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
@@ -3589,8 +3590,9 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);

	struct task_struct *p = current;

	unsigned long nr_reclaimed;

	unsigned int noreclaim_flag;



	p->flags |= PF_MEMALLOC;

	noreclaim_flag = memalloc_noreclaim_save();

	lockdep_set_current_reclaim_state(sc.gfp_mask);

	reclaim_state.reclaimed_slab = 0;

	p->reclaim_state = &reclaim_state;
@@ -3599,7 +3601,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 


	p->reclaim_state = NULL;

	lockdep_clear_current_reclaim_state();

	p->flags &= ~PF_MEMALLOC;

	memalloc_noreclaim_restore(noreclaim_flag);



	return nr_reclaimed;

}
@@ -3764,6 +3766,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in 
	struct task_struct *p = current;

	struct reclaim_state reclaim_state;

	int classzone_idx = gfp_zone(gfp_mask);

	unsigned int noreclaim_flag;

	struct scan_control sc = {

		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),

		.gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)),
@@ -3781,7 +3784,8 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in 
	 * and we also need to be able to write out pages for RECLAIM_WRITE

	 * and RECLAIM_UNMAP.

	 */

	p->flags |= PF_MEMALLOC | PF_SWAPWRITE;

	noreclaim_flag = memalloc_noreclaim_save();

	p->flags |= PF_SWAPWRITE;

	lockdep_set_current_reclaim_state(gfp_mask);

	reclaim_state.reclaimed_slab = 0;

	p->reclaim_state = &reclaim_state;
@@ -3797,7 +3801,8 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in 
	}



	p->reclaim_state = NULL;

	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);

	current->flags &= ~PF_SWAPWRITE;

	memalloc_noreclaim_restore(noreclaim_flag);

	lockdep_clear_current_reclaim_state();

	return sc.nr_reclaimed >= nr_pages;

}