Similarly to the page allocators, introduce slab-allocator specific alloc flags that internally control allocation behavior in addition to gfp_flags, without occupying the limited gfp flags space. Introduce the first flag SLAB_ALLOC_NOLOCK that behaves similarly to page allocator's ALLOC_TRYLOCK and will be used to reimplement kmalloc_nolock()'s "!allow_spin" behavior. That currently relies on gfpflags_allow_spinning() and thus the lack of both __GFP_RECLAIM flags, importantly __GFP_KSWAPD_RECLAIM. This can give false-positive results e.g. in early boot with a restricted gfp_allowed_mask. Also introduce alloc_flags_allow_spinning() to replace the usage of gfpflags_allow_spinning(). Start using alloc_flags and the new check first in alloc_from_pcs() and __pcs_replace_empty_main(). This means some slab allocations that were falsely treated as kmalloc_nolock() due to their gfp flags will now have higher chances of success, and this will further increase with followup changes. Remove a WARN_ON_ONCE() from refill_objects() as it's now legitimate to reach it from a slab allocation that's not _nolock() and yet lacks __GFP_KSWAPD_RECLAIM for other reasons. Link: https://patch.msgid.link/20260610-slab_alloc_flags-v2-5-7190909db118@kernel.org Reviewed-by: Harry Yoo (Oracle) Reviewed-by: Hao Li Reviewed-by: Suren Baghdasaryan Signed-off-by: Vlastimil Babka (SUSE) --- mm/slab.h | 9 +++++++++ mm/slub.c | 17 ++++++++--------- 2 files changed, 17 insertions(+), 9 deletions(-) diff --git a/mm/slab.h b/mm/slab.h index 1bf9c3021ae3..f1246f0c9f74 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -16,6 +16,15 @@ * Internal slab definitions */ +/* slab's alloc_flags definitions */ +#define SLAB_ALLOC_DEFAULT 0x00 /* no flags */ +#define SLAB_ALLOC_NOLOCK 0x01 /* a kmalloc_nolock() allocation */ + +static inline bool alloc_flags_allow_spinning(const unsigned int alloc_flags) +{ + return !(alloc_flags & SLAB_ALLOC_NOLOCK); +} + #ifdef CONFIG_64BIT # ifdef system_has_cmpxchg128 # define system_has_freelist_aba() system_has_cmpxchg128() diff --git a/mm/slub.c b/mm/slub.c index 8a0c5553876e..c53592baa027 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -4641,7 +4641,8 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, * unlocked. */ static struct slub_percpu_sheaves * -__pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, gfp_t gfp) +__pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, + gfp_t gfp, unsigned int alloc_flags) { struct slab_sheaf *empty = NULL; struct slab_sheaf *full; @@ -4667,7 +4668,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, return NULL; } - allow_spin = gfpflags_allow_spinning(gfp); + allow_spin = alloc_flags_allow_spinning(alloc_flags); full = barn_replace_empty_sheaf(barn, pcs->main, allow_spin); @@ -4753,7 +4754,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, } static __fastpath_inline -void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node) +void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, unsigned int alloc_flags, int node) { struct slub_percpu_sheaves *pcs; bool node_requested; @@ -4798,7 +4799,7 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node) pcs = this_cpu_ptr(s->cpu_sheaves); if (unlikely(pcs->main->size == 0)) { - pcs = __pcs_replace_empty_main(s, pcs, gfp); + pcs = __pcs_replace_empty_main(s, pcs, gfp, alloc_flags); if (unlikely(!pcs)) return NULL; } @@ -4931,7 +4932,7 @@ static __fastpath_inline void *slab_alloc_node(struct kmem_cache *s, struct list if (unlikely(object)) goto out; - object = alloc_from_pcs(s, gfpflags, node); + object = alloc_from_pcs(s, gfpflags, SLAB_ALLOC_DEFAULT, node); if (unlikely(!object)) { const struct slab_alloc_context ac = { @@ -5362,6 +5363,7 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in { gfp_t alloc_gfp = __GFP_NOWARN | __GFP_NOMEMALLOC | gfp_flags; size_t orig_size = size; + unsigned int alloc_flags = SLAB_ALLOC_NOLOCK; struct kmem_cache *s; bool can_retry = true; void *ret; @@ -5404,7 +5406,7 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in */ return NULL; - ret = alloc_from_pcs(s, alloc_gfp, node); + ret = alloc_from_pcs(s, alloc_gfp, alloc_flags, node); if (ret) goto success; @@ -7218,9 +7220,6 @@ refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min, unsigned int refilled; struct slab *slab; - if (WARN_ON_ONCE(!gfpflags_allow_spinning(gfp))) - return 0; - refilled = __refill_objects_node(s, p, gfp, min, max, get_node(s, local_node), /* allow_spin = */ true); -- 2.54.0