[PATCH 6/7] mm/page_alloc: Give GFP_ATOMIC and non-blocking allocations access to reserves

Mel Gorman
2023-01-09T15:19:05Z

Explicit GFP_ATOMIC allocations get flagged ALLOC_HARDER which is a bit
vague. In preparation for removing __GFP_ATOMIC, give GFP_ATOMIC and
other non-blocking allocation requests equal access to reserve. Rename
ALLOC_HARDER to ALLOC_NON_BLOCK to make it more clear what the flag
means.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/internal.h | 7 +++++--
mm/page_alloc.c | 23 +++++++++++++----------
2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 8706d46863df..23a37588073a 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -735,7 +735,10 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
#define ALLOC_OOM ALLOC_NO_WATERMARKS
#endif

-#define ALLOC_HARDER 0x10 /* try to alloc harder */
+#define ALLOC_NON_BLOCK 0x10 /* Caller cannot block. Allow access
+ * to 25% of the min watermark or
+ * 62.5% if __GFP_HIGH is set.
+ */
#define ALLOC_MIN_RESERVE 0x20 /* __GFP_HIGH set. Allow access to 50%
* of the min watermark.
*/
@@ -750,7 +753,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
#define ALLOC_KSWAPD 0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */

/* Flags that allow allocations below the min watermark. */
-#define ALLOC_RESERVES (ALLOC_HARDER|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
+#define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)

enum ttu_flags;
struct tlbflush_unmap_batch;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d2df78f5baa2..2217bab2dbb2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3999,7 +3999,7 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
* if it cannot get memory quickly, particularly if it's
* also __GFP_HIGH.
*/
- if (alloc_flags & ALLOC_HARDER)
+ if (alloc_flags & ALLOC_NON_BLOCK)
min -= min / 4;

/*
@@ -4851,28 +4851,30 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order)
* The caller may dip into page reserves a bit more if the caller
* cannot run direct reclaim, or if the caller has realtime scheduling
* policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will
- * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_MIN_RESERVE(__GFP_HIGH).
+ * set both ALLOC_NON_BLOCK and ALLOC_MIN_RESERVE(__GFP_HIGH).
*/
alloc_flags |= (__force int)
(gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM));

- if (gfp_mask & __GFP_ATOMIC) {
+ if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) {
/*
* Not worth trying to allocate harder for __GFP_NOMEMALLOC even
* if it can't schedule.
*/
if (!(gfp_mask & __GFP_NOMEMALLOC)) {
- alloc_flags |= ALLOC_HARDER;
+ alloc_flags |= ALLOC_NON_BLOCK;

if (order > 0)
alloc_flags |= ALLOC_HIGHATOMIC;
}

/*
- * Ignore cpuset mems for GFP_ATOMIC rather than fail, see the
- * comment for __cpuset_node_allowed().
+ * Ignore cpuset mems for non-blocking __GFP_HIGH (probably
+ * GFP_ATOMIC) rather than fail, see the comment for
+ * __cpuset_node_allowed().
*/
- alloc_flags &= ~ALLOC_CPUSET;
+ if (alloc_flags & ALLOC_MIN_RESERVE)
+ alloc_flags &= ~ALLOC_CPUSET;
} else if (unlikely(rt_task(current)) && in_task())
alloc_flags |= ALLOC_MIN_RESERVE;

@@ -5304,11 +5306,12 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,

/*
* Help non-failing allocations by giving them access to memory
- * reserves but do not use ALLOC_NO_WATERMARKS because this
+ * reserves normally used for high priority non-blocking
+ * allocations but do not use ALLOC_NO_WATERMARKS because this
* could deplete whole memory reserves which would just make
- * the situation worse
+ * the situation worse.
*/
- page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE|ALLOC_HARDER, ac);
+ page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE|ALLOC_NON_BLOCK, ac);
if (page)
goto got_pg;

--
2.35.3