This is a note to let you know that I've just added the patch titled
mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-page_alloc-explicitly-define-how-__gfp_high-non-b.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bda5b38029b455b098258a2defce2740d878718c
Author: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Date: Fri Jan 13 11:12:16 2023 +0000
mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves
[ Upstream commit 1ebbb21811b76c3b932959787f37985af36f62fa ]
GFP_ATOMIC allocations get flagged ALLOC_HARDER which is a vague
description. In preparation for the removal of GFP_ATOMIC redefine
__GFP_ATOMIC to simply mean non-blocking and renaming ALLOC_HARDER to
ALLOC_NON_BLOCK accordingly. __GFP_HIGH is required for access to
reserves but non-blocking is granted more access. For example, GFP_NOWAIT
is non-blocking but has no special access to reserves. A __GFP_NOFAIL
blocking allocation is granted access similar to __GFP_HIGH if the only
alternative is an OOM kill.
Link: https://lkml.kernel.org/r/20230113111217.14134-6-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>
Cc: Thierry Reding <thierry.reding@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Stable-dep-of: 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/mm/internal.h b/mm/internal.h
index 717e75313693c..cd444aa7a10af 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -592,7 +592,10 @@ 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.
*/
@@ -607,7 +610,7 @@ 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 7778c2b11d8cb..404cee30dcc26 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3878,18 +3878,19 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
* __GFP_HIGH allows access to 50% of the min reserve as well
* as OOM.
*/
- if (alloc_flags & ALLOC_MIN_RESERVE)
+ if (alloc_flags & ALLOC_MIN_RESERVE) {
min -= min / 2;
- /*
- * Non-blocking allocations can access some of the reserve
- * with more access if also __GFP_HIGH. The reasoning is that
- * a non-blocking caller may incur a more severe penalty
- * if it cannot get memory quickly, particularly if it's
- * also __GFP_HIGH.
- */
- if (alloc_flags & ALLOC_HARDER)
- min -= min / 4;
+ /*
+ * Non-blocking allocations (e.g. GFP_ATOMIC) can
+ * access more reserves than just __GFP_HIGH. Other
+ * non-blocking allocations requests such as GFP_NOWAIT
+ * or (GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) do not get
+ * access to the min reserve.
+ */
+ if (alloc_flags & ALLOC_NON_BLOCK)
+ min -= min / 4;
+ }
/*
* OOM victims can try even harder than the normal reserve
@@ -4729,28 +4730,30 @@ 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;
@@ -5188,12 +5191,13 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER);
/*
- * Help non-failing allocations by giving them access to memory
- * reserves but do not use ALLOC_NO_WATERMARKS because this
+ * Help non-failing allocations by giving some access to memory
+ * 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_HARDER, ac);
+ page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE, ac);
if (page)
goto got_pg;
