[patch 155/163] mm/page_alloc: fix memalloc_nocma_{save/restore} APIs

Andrew Morton
2020-08-07T06:26:11Z

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: mm/page_alloc: fix memalloc_nocma_{save/restore} APIs

Currently, memalloc_nocma_{save/restore} API that prevents CMA area
in page allocation is implemented by using current_gfp_context(). However,
there are two problems of this implementation.

First, this doesn't work for allocation fastpath. In the fastpath,
original gfp_mask is used since current_gfp_context() is introduced in
order to control reclaim and it is on slowpath. So, CMA area can be
allocated through the allocation fastpath even if
memalloc_nocma_{save/restore} APIs are used. Currently, there is just
one user for these APIs and it has a fallback method to prevent actual
problem.
Second, clearing __GFP_MOVABLE in current_gfp_context() has a side effect
to exclude the memory on the ZONE_MOVABLE for allocation target.

To fix these problems, this patch changes the implementation to exclude
CMA area in page allocation. Main point of this change is using the
alloc_flags. alloc_flags is mainly used to control allocation so it fits
for excluding CMA area in allocation.

Link: http://lkml.kernel.org/r/1595468942-29687-1-git-send-email-iamjoonsoo.kim@lge.com
Fixes: d7fefcc8de91 (mm/cma: add PF flag to force non cma alloc)
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/sched/mm.h | 8 +-------
mm/page_alloc.c | 31 +++++++++++++++++++++----------
2 files changed, 22 insertions(+), 17 deletions(-)

--- a/include/linux/sched/mm.h~mm-page_alloc-fix-memalloc_nocma_save-restore-apis
+++ a/include/linux/sched/mm.h
@@ -175,12 +175,10 @@ static inline bool in_vfork(struct task_
* Applies per-task gfp context to the given allocation flags.
* PF_MEMALLOC_NOIO implies GFP_NOIO
* PF_MEMALLOC_NOFS implies GFP_NOFS
- * PF_MEMALLOC_NOCMA implies no allocation from CMA region.
*/
static inline gfp_t current_gfp_context(gfp_t flags)
{
- if (unlikely(current->flags &
- (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_NOCMA))) {
+ if (unlikely(current->flags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS))) {
/*
* NOIO implies both NOIO and NOFS and it is a weaker context
* so always make sure it makes precedence
@@ -189,10 +187,6 @@ static inline gfp_t current_gfp_context(
flags &= ~(__GFP_IO | __GFP_FS);
else if (current->flags & PF_MEMALLOC_NOFS)
flags &= ~__GFP_FS;
-#ifdef CONFIG_CMA
- if (current->flags & PF_MEMALLOC_NOCMA)
- flags &= ~__GFP_MOVABLE;
-#endif
}
return flags;
}
--- a/mm/page_alloc.c~mm-page_alloc-fix-memalloc_nocma_save-restore-apis
+++ a/mm/page_alloc.c
@@ -2785,7 +2785,7 @@ __rmqueue(struct zone *zone, unsigned in
* allocating from CMA when over half of the zone's free memory
* is in the CMA area.
*/
- if (migratetype == MIGRATE_MOVABLE &&
+ if (alloc_flags & ALLOC_CMA &&
zone_page_state(zone, NR_FREE_CMA_PAGES) >
zone_page_state(zone, NR_FREE_PAGES) / 2) {
page = __rmqueue_cma_fallback(zone, order);
@@ -2796,7 +2796,7 @@ __rmqueue(struct zone *zone, unsigned in
retry:
page = __rmqueue_smallest(zone, order, migratetype);
if (unlikely(!page)) {
- if (migratetype == MIGRATE_MOVABLE)
+ if (alloc_flags & ALLOC_CMA)
page = __rmqueue_cma_fallback(zone, order);

if (!page && __rmqueue_fallback(zone, order, migratetype,
@@ -3687,6 +3687,20 @@ alloc_flags_nofragment(struct zone *zone
return alloc_flags;
}

+static inline unsigned int current_alloc_flags(gfp_t gfp_mask,
+ unsigned int alloc_flags)
+{
+#ifdef CONFIG_CMA
+ unsigned int pflags = current->flags;
+
+ if (!(pflags & PF_MEMALLOC_NOCMA) &&
+ gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
+ alloc_flags |= ALLOC_CMA;
+
+#endif
+ return alloc_flags;
+}
+
/*
* get_page_from_freelist goes through the zonelist trying to allocate
* a page.
@@ -4333,10 +4347,8 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
} else if (unlikely(rt_task(current)) && !in_interrupt())
alloc_flags |= ALLOC_HARDER;

-#ifdef CONFIG_CMA
- if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
- alloc_flags |= ALLOC_CMA;
-#endif
+ alloc_flags = current_alloc_flags(gfp_mask, alloc_flags);
+
return alloc_flags;
}

@@ -4637,7 +4649,7 @@ retry:

reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
if (reserve_flags)
- alloc_flags = reserve_flags;
+ alloc_flags = current_alloc_flags(gfp_mask, reserve_flags);

/*
* Reset the nodemask and zonelist iterators if memory policies can be
@@ -4714,7 +4726,7 @@ retry:

/* Avoid allocations with no watermarks from looping endlessly */
if (tsk_is_oom_victim(current) &&
- (alloc_flags == ALLOC_OOM ||
+ (alloc_flags & ALLOC_OOM ||
(gfp_mask & __GFP_NOMEMALLOC)))
goto nopage;

@@ -4806,8 +4818,7 @@ static inline bool prepare_alloc_pages(g
if (should_fail_alloc_page(gfp_mask, order))
return false;

- if (IS_ENABLED(CONFIG_CMA) && ac->migratetype == MIGRATE_MOVABLE)
- *alloc_flags |= ALLOC_CMA;
+ *alloc_flags = current_alloc_flags(gfp_mask, *alloc_flags);

return true;
}
_