Atomic allocations (GFP_ATOMIC) are prone to failure under heavy memory pressure as they cannot enter direct reclaim. Handle these failures by introducing a watermark boost mechanism for atomic requests. Refactor boost_watermark() using an internal helper to support both fragmentation and atomic paths. Apply zone-proportional boosts (~0.1% of managed pages) for atomic allocations, while decoupling it from watermark_boost_factor. Implement boost_zones_for_atomic() to iterate through and boost all eligible zones in the zonelist, respecting nodemasks. Use a per-zone 1-second debounce timer via last_boost_jiffies to prevent excessive boosting. Protect modifications with zone->lock and verify with lockdep. Integrate the mechanism into the page allocation slowpath specifically for order-0 GFP_ATOMIC requests. This approach reuses existing infrastructure and ensures emergency reserves even if fragmentation boosting is disabled. 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 Acked-by: Vlastimil Babka Signed-off-by: Qiliang Yuan --- v10: - Refactor watermark boosting into mechanism (__boost_watermark) and policy logic. - Decouple Atomic boost from watermark_boost_factor to ensure emergency reserves. - Simplify Atomic boost calculation to ~0.1% of managed pages with a 10% high-WM cap. - Boost all eligible zones in the zonelist while respecting nodemasks. v9: - Use mult_frac() for boost calculation. - Add !can_direct_reclaim check. - Code cleanup: naming, scope, and line limits. - Update tags: Add Vlastimil's Acked-by. - Link: https://lore.kernel.org/r/20260213-wujing-mm-page_alloc-v8-v9-1-cd99f3a6cb70@gmail.com v8: - Use spin_lock_irqsave() to prevent inconsistent lock state. v7: - Use local variable for boost_amount. - Add zone->lock protection. - Add lockdep assertion. v6: - Use ATOMIC_BOOST_SCALE_SHIFT define. - Add documentation for 0.1% rationale. v5: - Use native boost_watermark(). v4: - Add watermark_scale_boost and gradual decay. v3: - Per-zone debounce timer. v2: - Debounce logic and zone-proportional boosting. v1: - Initial version. --- include/linux/mmzone.h | 1 + mm/page_alloc.c | 77 ++++++++++++++++++++++++++++++++++++++++++++------ 2 files changed, 69 insertions(+), 9 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 75ef7c9f9307..8e37e4e6765b 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -882,6 +882,7 @@ struct zone { /* zone watermarks, access with *_wmark_pages(zone) macros */ unsigned long _watermark[NR_WMARK]; unsigned long watermark_boost; + unsigned long last_boost_jiffies; unsigned long nr_reserved_highatomic; unsigned long nr_free_highatomic; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c380f063e8b7..9219bfca806b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2158,12 +2158,15 @@ bool pageblock_unisolate_and_move_free_pages(struct zone *zone, struct page *pag #endif /* CONFIG_MEMORY_ISOLATION */ -static inline bool boost_watermark(struct zone *zone) +/* + * Helper for boosting watermarks. Called with zone->lock held. + * Use max_boost to limit the boost to a percentage of the high watermark. + */ +static inline bool __boost_watermark(struct zone *zone, unsigned long amount, + unsigned long max_boost) { - unsigned long max_boost; + lockdep_assert_held(&zone->lock); - if (!watermark_boost_factor) - return false; /* * Don't bother in zones that are unlikely to produce results. * On small machines, including kdump capture kernels running @@ -2173,9 +2176,6 @@ static inline bool boost_watermark(struct zone *zone) if ((pageblock_nr_pages * 4) > zone_managed_pages(zone)) return false; - max_boost = mult_frac(zone->_watermark[WMARK_HIGH], - watermark_boost_factor, 10000); - /* * high watermark may be uninitialised if fragmentation occurs * very early in boot so do not boost. We do not fall @@ -2189,12 +2189,67 @@ static inline bool boost_watermark(struct zone *zone) max_boost = max(pageblock_nr_pages, max_boost); - zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, - max_boost); + zone->watermark_boost = min(zone->watermark_boost + amount, + max_boost); return true; } +/* + * Boost watermarks to increase reclaim pressure when fragmentation occurs + * and we fall back to other migratetypes. + */ +static inline bool boost_watermark(struct zone *zone) +{ + if (!watermark_boost_factor) + return false; + + return __boost_watermark(zone, pageblock_nr_pages, + mult_frac(zone->_watermark[WMARK_HIGH], + watermark_boost_factor, 10000)); +} + +/* + * Boost watermarks by ~0.1% of zone size on atomic allocation pressure. + * This provides zone-proportional safety buffers: ~1MB per 1GB of zone + * size. Max boost ceiling is fixed at ~10% of high watermark. + * + * This emergency reserve is independent of watermark_boost_factor. + */ +static inline bool boost_watermark_atomic(struct zone *zone) +{ + return __boost_watermark(zone, + max(pageblock_nr_pages, zone_managed_pages(zone) / 1000), + zone->_watermark[WMARK_HIGH] / 10); +} + +static void boost_zones_for_atomic(struct alloc_context *ac, gfp_t gfp_mask) +{ + struct zoneref *z; + struct zone *zone; + unsigned long now = jiffies; + + for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, + ac->highest_zoneidx, ac->nodemask) { + /* Rate-limit boosts to once per second per zone */ + if (time_after(now, zone->last_boost_jiffies + HZ)) { + unsigned long flags; + bool should_wake; + + zone->last_boost_jiffies = now; + + /* Modify watermark under lock, wake kswapd outside */ + spin_lock_irqsave(&zone->lock, flags); + should_wake = boost_watermark_atomic(zone); + spin_unlock_irqrestore(&zone->lock, flags); + + if (should_wake) + wakeup_kswapd(zone, gfp_mask, 0, + ac->highest_zoneidx); + } + } +} + /* * When we are falling back to another migratetype during allocation, should we * try to claim an entire block to satisfy further allocations, instead of @@ -4742,6 +4797,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, if (page) goto got_pg; + /* Boost watermarks for atomic requests entering slowpath */ + if (((gfp_mask & GFP_ATOMIC) == GFP_ATOMIC) && order == 0 && !can_direct_reclaim) + boost_zones_for_atomic(ac, gfp_mask); + /* * For costly allocations, try direct compaction first, as it's likely * that we have enough base pages and don't need to reclaim. For non- --- base-commit: b54345928fa1dbde534e32ecaa138678fd5d2135 change-id: 20260206-wujing-mm-page_alloc-v8-fb1979bac6fe Best regards, -- Qiliang Yuan