[PATCH 3/6] mm/page_alloc: Explicitly record high-order atomic allocations in alloc_flags

From: Mel Gorman
Date: Tue Nov 29 2022 - 10:18:11 EST


A high-order ALLOC_HARDER allocation is assumed to be atomic. While that
is accurate, it changes later in the series. In preparation, explicitly
record high-order atomic allocations in gfp_to_alloc_flags().

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
mm/internal.h | 1 +
mm/page_alloc.c | 19 +++++++++++++------
2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index d503e57a57a1..9a9d9b5ee87f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -754,6 +754,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
#else
#define ALLOC_NOFRAGMENT 0x0
#endif
+#define ALLOC_HIGHATOMIC 0x200 /* Allows access to MIGRATE_HIGHATOMIC */
#define ALLOC_KSWAPD 0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */

enum ttu_flags;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index da746e9eb2cf..e2b65767dda0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3710,7 +3710,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
* reserved for high-order atomic allocation, so order-0
* request should skip it.
*/
- if (order > 0 && alloc_flags & ALLOC_HARDER)
+ if (alloc_flags & ALLOC_HIGHATOMIC)
page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
if (!page) {
page = __rmqueue(zone, order, migratetype, alloc_flags);
@@ -4028,8 +4028,10 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
return true;
}
#endif
- if (alloc_harder && !free_area_empty(area, MIGRATE_HIGHATOMIC))
+ if ((alloc_flags & ALLOC_HIGHATOMIC) &&
+ !free_area_empty(area, MIGRATE_HIGHATOMIC)) {
return true;
+ }
}
return false;
}
@@ -4291,7 +4293,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
* If this is a high-order atomic allocation then check
* if the pageblock should be reserved for the future
*/
- if (unlikely(order && (alloc_flags & ALLOC_HARDER)))
+ if (unlikely(alloc_flags & ALLOC_HIGHATOMIC))
reserve_highatomic_pageblock(page, zone, order);

return page;
@@ -4818,7 +4820,7 @@ static void wake_all_kswapds(unsigned int order, gfp_t gfp_mask,
}

static inline unsigned int
-gfp_to_alloc_flags(gfp_t gfp_mask)
+gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order)
{
unsigned int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;

@@ -4844,8 +4846,13 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
* Not worth trying to allocate harder for __GFP_NOMEMALLOC even
* if it can't schedule.
*/
- if (!(gfp_mask & __GFP_NOMEMALLOC))
+ if (!(gfp_mask & __GFP_NOMEMALLOC)) {
alloc_flags |= ALLOC_HARDER;
+
+ if (order > 0)
+ alloc_flags |= ALLOC_HIGHATOMIC;
+ }
+
/*
* Ignore cpuset mems for GFP_ATOMIC rather than fail, see the
* comment for __cpuset_node_allowed().
@@ -5053,7 +5060,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* kswapd needs to be woken up, and to avoid the cost of setting up
* alloc_flags precisely. So we do that now.
*/
- alloc_flags = gfp_to_alloc_flags(gfp_mask);
+ alloc_flags = gfp_to_alloc_flags(gfp_mask, order);

/*
* We need to recalculate the starting point for the zonelist iterator
--
2.35.3