Re: [PATCH 2/4] mm: introduce memalloc_noreclaim_{save,restore}

2017-04-07 Thread Hillf Danton 

On April 05, 2017 3:47 PM Vlastimil Babka wrote: 
> 
> The previous patch 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.
> 
> Suggested-by: Michal Hocko 
> Signed-off-by: Vlastimil Babka 
> ---

Acked-by: Hillf Danton

Re: [PATCH 2/4] mm: introduce memalloc_noreclaim_{save,restore}

2017-04-05 Thread Michal Hocko 
On Wed 05-04-17 09:46:58, Vlastimil Babka wrote:
> The previous patch 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.
> 
> Suggested-by: Michal Hocko 
> Signed-off-by: Vlastimil Babka 

One could argue that tsk_restore_flags() could be extended to provide
tsk_set_flags() and use it for all allocation related PF flags. I do not
have a strong opinion on that but explicit API sounds a bit better to me
because is easier to follow (at least for me). If others think that
generic API would be better then I won't have any objections. Anyway
this looks good to me.
Acked-by: Michal Hocko 

> ---
>  include/linux/sched/mm.h | 12 
>  mm/page_alloc.c  | 11 ++-
>  mm/vmscan.c  | 17 +++--
>  3 files changed, 29 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 9daabe138c99..2b24a6974847 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -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 */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b84e6ffbe756..037e32dccd7a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3288,15 +3288,15 @@ __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;
> @@ -3443,12 +3443,13 @@ __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 = _state;
> @@ -3458,7 +3459,7 @@ __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();
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 58615bb27f2f..ff63b91a0f48 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2992,6 +2992,7 @@ 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) |
> @@ -3018,9 +3019,9 @@ 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, );
> - current->flags &= ~PF_MEMALLOC;
> + memalloc_noreclaim_restore(noreclaim_flag);
>  
>   trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
>  
> @@ -3544,8 +3545,9 @@ unsigned long shrink_all_memory(unsigned long 
> nr_to_reclaim)
>   struct

[PATCH 2/4] mm: introduce memalloc_noreclaim_{save,restore}

2017-04-05 Thread Vlastimil Babka 
The previous patch 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.

Suggested-by: Michal Hocko 
Signed-off-by: Vlastimil Babka 
---
 include/linux/sched/mm.h | 12 
 mm/page_alloc.c  | 11 ++-
 mm/vmscan.c  | 17 +++--
 3 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 9daabe138c99..2b24a6974847 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -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 */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b84e6ffbe756..037e32dccd7a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3288,15 +3288,15 @@ __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;
@@ -3443,12 +3443,13 @@ __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 = _state;
@@ -3458,7 +3459,7 @@ __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();
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 58615bb27f2f..ff63b91a0f48 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2992,6 +2992,7 @@ 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) |
@@ -3018,9 +3019,9 @@ 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, );
-   current->flags &= ~PF_MEMALLOC;
+   memalloc_noreclaim_restore(noreclaim_flag);
 
trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
 
@@ -3544,8 +3545,9 @@ 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 = _state;
@@ -3554,7 +3556,7 @@ unsigned long shrink_all_memory(unsigned long 
nr_to_reclaim)
 
p->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
-   p->flags &= ~PF_MEMALLOC;
+