5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
[ Upstream commit 524c48072e5673f4511f1ad81493e2485863fd65 ]
Patch series "Discard __GFP_ATOMIC", v3.
Neil's patch has been residing in mm-unstable as commit 2fafb4fe8f7a ("mm:
discard __GFP_ATOMIC") for a long time and recently brought up again.
Most recently, I was worried that __GFP_HIGH allocations could use
high-order atomic reserves which is unintentional but there was no
response so lets revisit -- this series reworks how min reserves are used,
protects highorder reserves and then finishes with Neil's patch with very
minor modifications so it fits on top.
There was a review discussion on renaming __GFP_DIRECT_RECLAIM to
__GFP_ALLOW_BLOCKING but I didn't think it was that big an issue and is
orthogonal to the removal of __GFP_ATOMIC.
There were some concerns about how the gfp flags affect the min reserves
but it never reached a solid conclusion so I made my own attempt.
The series tries to iron out some of the details on how reserves are used.
ALLOC_HIGH becomes ALLOC_MIN_RESERVE and ALLOC_HARDER becomes
ALLOC_NON_BLOCK and documents how the reserves are affected. For example,
ALLOC_NON_BLOCK (no direct reclaim) on its own allows 25% of the min
reserve. ALLOC_MIN_RESERVE (__GFP_HIGH) allows 50% and both combined
allows deeper access again. ALLOC_OOM allows access to 75%.
High-order atomic allocations are explicitly handled with the caveat that
no __GFP_ATOMIC flag means that any high-order allocation that specifies
GFP_HIGH and cannot enter direct reclaim will be treated as if it was
GFP_ATOMIC.
This patch (of 6):
__GFP_HIGH aliases to ALLOC_HIGH but the name does not really hint what it
means. As ALLOC_HIGH is internal to the allocator, rename it to
ALLOC_MIN_RESERVE to document that the min reserves can be depleted.
Link: https://lkml.kernel.org/r/20230113111217.14134-1-mgorman@xxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20230113111217.14134-2-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>
Cc: Thierry Reding <thierry.reding@xxxxxxxxx>
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>
---
mm/internal.h | 4 +++-
mm/page_alloc.c | 8 ++++----
2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index cf3cb933eba3f..e6c96327b5855 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -593,7 +593,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
#endif
#define ALLOC_HARDER 0x10 /* try to alloc harder */
-#define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
+#define ALLOC_MIN_RESERVE 0x20 /* __GFP_HIGH set. Allow access to 50%
+ * of the min watermark.
+ */
#define ALLOC_CPUSET 0x40 /* check for correct cpuset */
#define ALLOC_CMA 0x80 /* allow allocations from CMA areas */
#ifdef CONFIG_ZONE_DMA32
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ae628574dc9fc..4e9e9cb98f336 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3865,7 +3865,7 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
/* free_pages may go negative - that's OK */
free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);
- if (alloc_flags & ALLOC_HIGH)
+ if (alloc_flags & ALLOC_MIN_RESERVE)
min -= min / 2;
if (unlikely(alloc_harder)) {
@@ -4696,18 +4696,18 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
unsigned int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
/*
- * __GFP_HIGH is assumed to be the same as ALLOC_HIGH
+ * __GFP_HIGH is assumed to be the same as ALLOC_MIN_RESERVE
* and __GFP_KSWAPD_RECLAIM is assumed to be the same as ALLOC_KSWAPD
* to save two branches.
*/
- BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
+ BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_MIN_RESERVE);
BUILD_BUG_ON(__GFP_KSWAPD_RECLAIM != (__force gfp_t) ALLOC_KSWAPD);
/*
* 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_HIGH (__GFP_HIGH).
+ * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_MIN_RESERVE(__GFP_HIGH).
*/
alloc_flags |= (__force int)
(gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM));
--
2.43.0
