Willem de Bruijn b71a75739a bpf: Adjust free target to avoid global starvation of LRU map ... [ Upstream commit d4adf1c9ee ] BPF_MAP_TYPE_LRU_HASH can recycle most recent elements well before the map is full, due to percpu reservations and force shrink before neighbor stealing. Once a CPU is unable to borrow from the global map, it will once steal one elem from a neighbor and after that each time flush this one element to the global list and immediately recycle it. Batch value LOCAL_FREE_TARGET (128) will exhaust a 10K element map with 79 CPUs. CPU 79 will observe this behavior even while its neighbors hold 78 * 127 + 1 * 15 == 9921 free elements (99%). CPUs need not be active concurrently. The issue can appear with affinity migration, e.g., irqbalance. Each CPU can reserve and then hold onto its 128 elements indefinitely. Avoid global list exhaustion by limiting aggregate percpu caches to half of map size, by adjusting LOCAL_FREE_TARGET based on cpu count. This change has no effect on sufficiently large tables. Similar to LOCAL_NR_SCANS and lru->nr_scans, introduce a map variable lru->free_target. The extra field fits in a hole in struct bpf_lru. The cacheline is already warm where read in the hot path. The field is only accessed with the lru lock held. Tested-by: Anton Protopopov <a.s.protopopov@gmail.com> Signed-off-by: Willem de Bruijn <willemb@google.com> Acked-by: Stanislav Fomichev <sdf@fomichev.me> Link: https://lore.kernel.org/r/20250618215803.3587312-1-willemdebruijn.kernel@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2025-07-17 18:35:21 +02:00
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ABI	x86/bugs: Add a Transient Scheduler Attacks mitigation	2025-07-10 16:03:21 +02:00
accel
accounting
admin-guide	x86/bugs: Add a Transient Scheduler Attacks mitigation	2025-07-10 16:03:21 +02:00
arch	x86/bugs: Rename MDS machinery to something more generic	2025-07-10 16:03:21 +02:00
block
bpf	bpf: Adjust free target to avoid global starvation of LRU map	2025-07-17 18:35:21 +02:00
cdrom
core-api	module: Provide EXPORT_SYMBOL_GPL_FOR_MODULES() helper	2025-07-10 16:03:18 +02:00
cpu-freq
crypto
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devicetree	dt-bindings: serial: 8250: Make clocks and clock-frequency exclusive	2025-07-06 11:00:13 +02:00
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fault-injection
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networking	strparser: Add read_sock callback	2025-02-27 04:10:50 -08:00
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scheduler	sched/topology: Consolidate and clean up access to a CPU's max compute capacity	2025-05-02 07:50:41 +02:00
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timers	sched/isolation: Prevent boot crash when the boot CPU is nohz_full	2025-03-22 12:50:37 -07:00
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