linux-kernel - [PATCH 15/21] mm/page_alloc: rename ALLOC_NON_BLOCK back to

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Message-ID: <20250924-b4-asi-page-alloc-v1-15-2d861768041f@google.com>
Date: Wed, 24 Sep 2025 14:59:50 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: jackmanb@...gle.com, Andy Lutomirski <luto@...nel.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
	Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>
Cc: peterz@...radead.org, bp@...en8.de, dave.hansen@...ux.intel.com, 
	mingo@...hat.com, tglx@...utronix.de, akpm@...ux-foundation.org, 
	david@...hat.com, derkling@...gle.com, junaids@...gle.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, reijiw@...gle.com, 
	rientjes@...gle.com, rppt@...nel.org, vbabka@...e.cz, x86@...nel.org, 
	yosry.ahmed@...ux.dev
Subject: [PATCH 15/21] mm/page_alloc: rename ALLOC_NON_BLOCK back to _HARDER

Commit 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH
non-blocking allocations accesses reserves") renamed ALLOC_HARDER to
ALLOC_NON_BLOCK because the former is "a vague description".

However, vagueness is accurate here, this is a vague flag. It is not set
for __GFP_NOMEMALLOC. It doesn't really mean "allocate without blocking"
but rather "allow dipping into atomic reserves, _because_ of the need
not to block".

A later commit will need an alloc flag that really means "don't block
here", so go back to the flag's old name and update the commentary
to try and give it a slightly clearer meaning.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 mm/internal.h   | 9 +++++----
 mm/page_alloc.c | 8 ++++----
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 6006cfb2b9c7e771a0c647c471901dc7fcdad242..513aba6c00bed813c9e38464aec5a15e65edaa58 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1297,9 +1297,10 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 #define ALLOC_OOM		ALLOC_NO_WATERMARKS
 #endif
 
-#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_HARDER		 0x10 /* Because the 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.
@@ -1316,7 +1317,7 @@ 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_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
+#define ALLOC_RESERVES (ALLOC_HARDER|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 0b205aefd27e188c492c32754db08a4488317bd8..cd47cfaae820ce696d2e6e0c47436e00d3feef60 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3295,7 +3295,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
 			 * reserves as failing now is worse than failing a
 			 * high-order atomic allocation in the future.
 			 */
-			if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK)))
+			if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_HARDER)))
 				page = __rmqueue_smallest(zone, order, ft_high);
 
 			if (!page) {
@@ -3662,7 +3662,7 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 			 * or (GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) do not get
 			 * access to the min reserve.
 			 */
-			if (alloc_flags & ALLOC_NON_BLOCK)
+			if (alloc_flags & ALLOC_HARDER)
 				min -= min / 4;
 		}
 
@@ -4546,7 +4546,7 @@ 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_NON_BLOCK and ALLOC_MIN_RESERVE(__GFP_HIGH).
+	 * set both ALLOC_HARDER and ALLOC_MIN_RESERVE(__GFP_HIGH).
 	 */
 	alloc_flags |= (__force int)
 		(gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM));
@@ -4557,7 +4557,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order)
 		 * if it can't schedule.
 		 */
 		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
-			alloc_flags |= ALLOC_NON_BLOCK;
+			alloc_flags |= ALLOC_HARDER;
 
 			if (order > 0 && (alloc_flags & ALLOC_MIN_RESERVE))
 				alloc_flags |= ALLOC_HIGHATOMIC;

-- 
2.50.1