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Subject[PATCH 2/3] mm, page_alloc: Split alloc_pages_nodemask
Date
alloc_pages_nodemask does a number of preperation steps that determine
what zones can be used for the allocation depending on a variety of
factors. This is fine but a hypothetical caller that wanted multiple
order-0 pages has to do the preparation steps multiple times. This patch
structures __alloc_pages_nodemask such that it's relatively easy to build
a bulk order-0 page allocator. There is no functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
---
mm/page_alloc.c | 81 ++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 49 insertions(+), 32 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d8798583eaf8..4a602b7f258d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3762,64 +3762,81 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
return page;
}

-/*
- * This is the 'heart' of the zoned buddy allocator.
- */
-struct page *
-__alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
- struct zonelist *zonelist, nodemask_t *nodemask)
+static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
+ struct zonelist *zonelist, nodemask_t *nodemask,
+ struct alloc_context *ac, gfp_t *alloc_mask,
+ unsigned int *alloc_flags)
{
- struct page *page;
- unsigned int cpuset_mems_cookie;
- unsigned int alloc_flags = ALLOC_WMARK_LOW;
- gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
- struct alloc_context ac = {
- .high_zoneidx = gfp_zone(gfp_mask),
- .zonelist = zonelist,
- .nodemask = nodemask,
- .migratetype = gfpflags_to_migratetype(gfp_mask),
- };
+ ac->high_zoneidx = gfp_zone(gfp_mask);
+ ac->zonelist = zonelist;
+ ac->nodemask = nodemask;
+ ac->migratetype = gfpflags_to_migratetype(gfp_mask);

if (cpusets_enabled()) {
- alloc_mask |= __GFP_HARDWALL;
- alloc_flags |= ALLOC_CPUSET;
- if (!ac.nodemask)
- ac.nodemask = &cpuset_current_mems_allowed;
+ *alloc_mask |= __GFP_HARDWALL;
+ *alloc_flags |= ALLOC_CPUSET;
+ if (!ac->nodemask)
+ ac->nodemask = &cpuset_current_mems_allowed;
}

- gfp_mask &= gfp_allowed_mask;
-
lockdep_trace_alloc(gfp_mask);

might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM);

if (should_fail_alloc_page(gfp_mask, order))
- return NULL;
+ return false;

/*
* Check the zones suitable for the gfp_mask contain at least one
* valid zone. It's possible to have an empty zonelist as a result
* of __GFP_THISNODE and a memoryless node
*/
- if (unlikely(!zonelist->_zonerefs->zone))
- return NULL;
+ if (unlikely(!ac->zonelist->_zonerefs->zone))
+ return false;

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

-retry_cpuset:
- cpuset_mems_cookie = read_mems_allowed_begin();
+ return true;
+}

+/* Determine whether to spread dirty pages and what the first usable zone */
+static inline void finalise_ac(gfp_t gfp_mask,
+ unsigned int order, struct alloc_context *ac)
+{
/* Dirty zone balancing only done in the fast path */
- ac.spread_dirty_pages = (gfp_mask & __GFP_WRITE);
+ ac->spread_dirty_pages = (gfp_mask & __GFP_WRITE);

/*
* The preferred zone is used for statistics but crucially it is
* also used as the starting point for the zonelist iterator. It
* may get reset for allocations that ignore memory policies.
*/
- ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
- ac.high_zoneidx, ac.nodemask);
+ ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
+ ac->high_zoneidx, ac->nodemask);
+}
+
+/*
+ * This is the 'heart' of the zoned buddy allocator.
+ */
+struct page *
+__alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
+ struct zonelist *zonelist, nodemask_t *nodemask)
+{
+ struct page *page;
+ unsigned int cpuset_mems_cookie;
+ unsigned int alloc_flags = ALLOC_WMARK_LOW;
+ gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
+ struct alloc_context ac = { };
+
+ gfp_mask &= gfp_allowed_mask;
+ if (!prepare_alloc_pages(gfp_mask, order, zonelist, nodemask, &ac, &alloc_mask, &alloc_flags))
+ return NULL;
+
+retry_cpuset:
+ cpuset_mems_cookie = read_mems_allowed_begin();
+
+ finalise_ac(gfp_mask, order, &ac);
if (!ac.preferred_zoneref) {
page = NULL;
goto no_zone;
--
2.11.0
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