From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- mm/cma.h | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 96 insertions(+) create mode 100644 mm/cma.h (limited to 'mm/cma.h') diff --git a/mm/cma.h b/mm/cma.h new file mode 100644 index 000000000..ab6d39898 --- /dev/null +++ b/mm/cma.h @@ -0,0 +1,96 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __MM_CMA_H__ +#define __MM_CMA_H__ + +#include +#include +#include + +struct cma_kobject { + struct kobject kobj; + struct cma *cma; +}; + +/* + * Multi-range support. This can be useful if the size of the allocation + * is not expected to be larger than the alignment (like with hugetlb_cma), + * and the total amount of memory requested, while smaller than the total + * amount of memory available, is large enough that it doesn't fit in a + * single physical memory range because of memory holes. + * + * Fields: + * @base_pfn: physical address of range + * @early_pfn: first PFN not reserved through cma_reserve_early + * @count: size of range + * @bitmap: bitmap of allocated (1 << order_per_bit)-sized chunks. + */ +struct cma_memrange { + unsigned long base_pfn; + unsigned long count; + union { + unsigned long early_pfn; + unsigned long *bitmap; + }; +#ifdef CONFIG_CMA_DEBUGFS + struct debugfs_u32_array dfs_bitmap; +#endif +}; +#define CMA_MAX_RANGES 8 + +struct cma { + unsigned long count; + unsigned long available_count; + unsigned int order_per_bit; /* Order of pages represented by one bit */ + spinlock_t lock; + struct mutex alloc_mutex; +#ifdef CONFIG_CMA_DEBUGFS + struct hlist_head mem_head; + spinlock_t mem_head_lock; +#endif + char name[CMA_MAX_NAME]; + int nranges; + struct cma_memrange ranges[CMA_MAX_RANGES]; +#ifdef CONFIG_CMA_SYSFS + /* the number of CMA page successful allocations */ + atomic64_t nr_pages_succeeded; + /* the number of CMA page allocation failures */ + atomic64_t nr_pages_failed; + /* the number of CMA page released */ + atomic64_t nr_pages_released; + /* kobject requires dynamic object */ + struct cma_kobject *cma_kobj; +#endif + unsigned long flags; + /* NUMA node (NUMA_NO_NODE if unspecified) */ + int nid; +}; + +enum cma_flags { + CMA_RESERVE_PAGES_ON_ERROR, + CMA_ZONES_VALID, + CMA_ZONES_INVALID, + CMA_ACTIVATED, +}; + +extern struct cma cma_areas[MAX_CMA_AREAS]; +extern unsigned int cma_area_count; + +static inline unsigned long cma_bitmap_maxno(struct cma *cma, + struct cma_memrange *cmr) +{ + return cmr->count >> cma->order_per_bit; +} + +#ifdef CONFIG_CMA_SYSFS +void cma_sysfs_account_success_pages(struct cma *cma, unsigned long nr_pages); +void cma_sysfs_account_fail_pages(struct cma *cma, unsigned long nr_pages); +void cma_sysfs_account_release_pages(struct cma *cma, unsigned long nr_pages); +#else +static inline void cma_sysfs_account_success_pages(struct cma *cma, + unsigned long nr_pages) {}; +static inline void cma_sysfs_account_fail_pages(struct cma *cma, + unsigned long nr_pages) {}; +static inline void cma_sysfs_account_release_pages(struct cma *cma, + unsigned long nr_pages) {}; +#endif +#endif -- cgit v1.3.1