linux-kernel - [PATCH] mm/page_alloc: boost watermarks on atomic allocation failure

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Message-ID: <20260122020035.227449-1-realwujing@gmail.com>
Date: Wed, 21 Jan 2026 21:00:35 -0500
From: Qiliang Yuan <realwujing@...il.com>
To: akpm@...ux-foundation.org
Cc: david@...nel.org,
	mhocko@...e.com,
	vbabka@...e.cz,
	willy@...radead.org,
	lance.yang@...ux.dev,
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	jackmanb@...gle.com,
	ziy@...dia.com,
	weixugc@...gle.com,
	rppt@...nel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
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	edumazet@...gle.com,
	jis1@...natelecom.cn,
	wangh13@...natelecom.cn,
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	sunshx@...natelecom.cn,
	zhangzq20@...natelecom.cn,
	zhangjn11@...natelecom.cn,
	Qiliang Yuan <realwujing@...il.com>,
	Qiliang Yuan <yuanql9@...natelecom.cn>
Subject: [PATCH] mm/page_alloc: boost watermarks on atomic allocation failure

Atomic allocations (GFP_ATOMIC) are prone to failure under heavy memory
pressure as they cannot enter direct reclaim. This patch introduces a
'Soft Boost' mechanism to mitigate this.

When a GFP_ATOMIC request fails or enters the slowpath, the preferred
zone's watermark_boost is increased. This triggers kswapd to proactively
reclaim memory, creating a safety buffer for future atomic bursts.

To prevent excessive reclaim during packet storms, a 1-second debounce
timer (last_boost_jiffies) is added to each zone to rate-limit boosts.

This approach reuses existing watermark_boost infrastructure, ensuring
minimal overhead and asynchronous background reclaim via kswapd.

Allocation failure logs:
[38535644.718700] node 0: slabs: 1031, objs: 43328, free: 0
[38535644.725059] node 1: slabs: 339, objs: 17616, free: 317
[38535645.428345] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
[38535645.436888] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
[38535645.447664] node 0: slabs: 940, objs: 40864, free: 144
[38535645.454026] node 1: slabs: 322, objs: 19168, free: 383
[38535645.556122] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
[38535645.564576] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
[38535649.655523] warn_alloc: 59 callbacks suppressed
[38535649.655527] swapper/100: page allocation failure: order:0, mode:0x480020(GFP_ATOMIC), nodemask=(null)
[38535649.671692] swapper/100 cpuset=/ mems_allowed=0-1

Signed-off-by: Qiliang Yuan <realwujing@...il.com>
Signed-off-by: Qiliang Yuan <yuanql9@...natelecom.cn>
---
v6:
  - Replace magic number ">> 10" with ATOMIC_BOOST_SCALE_SHIFT define
  - Add documentation explaining 0.1% zone size boost rationale
v5:
  - Simplify to use native boost_watermark() instead of custom logic
v4:
  - Add watermark_scale_boost and gradual decay via balance_pgdat
v3:
  - Move debounce timer to per-zone; optimize zone selection
v2:
  - Add debounce logic and zone-proportional boosting
v1:
  - Initial: boost min_free_kbytes on GFP_ATOMIC failure
---
 include/linux/mmzone.h |  1 +
 mm/page_alloc.c        | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)
---
 mm/page_alloc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1faace9e2dc5..8ea2435125d5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -218,6 +218,13 @@ unsigned int pageblock_order __read_mostly;
 static void __free_pages_ok(struct page *page, unsigned int order,
 			    fpi_t fpi_flags);
 
+/*
+ * Boost watermarks by ~0.1% of zone size on atomic allocation pressure.
+ * This provides zone-proportional safety buffers: ~1MB per 1GB of zone size.
+ * Larger zones under GFP_ATOMIC pressure need proportionally larger reserves.
+ */
+#define ATOMIC_BOOST_SCALE_SHIFT 10
+
 /*
  * results with 256, 32 in the lowmem_reserve sysctl:
  *	1G machine -> (16M dma, 800M-16M normal, 1G-800M high)
@@ -2190,7 +2197,7 @@ static inline bool boost_watermark(struct zone *zone)
 	max_boost = max(pageblock_nr_pages, max_boost);
 
 	zone->watermark_boost = min(zone->watermark_boost +
-		max(pageblock_nr_pages, zone_managed_pages(zone) >> 10),
+		max(pageblock_nr_pages, zone_managed_pages(zone) >> ATOMIC_BOOST_SCALE_SHIFT),
 		max_boost);
 
 	return true;
-- 
2.51.0