On 7/20/26 14:44, Harry Yoo (Oracle) wrote: > Teach kfree_rcu_sheaf() how to handle the !allow_spin case. Try to get > an empty sheaf from pcs->spare or the barn even when spinning is not > allowed. Unlike __pcs_replace_full_main(), try harder to allocate > an empty sheaf because the fallback path will be more expensive than > kfree_nolock(). > > Now that slab has internal alloc_flags to describe context, introduce > free_flags analogously and convert free_flags to alloc_flags when > allocating memory in the free path. alloc_empty_sheaf() now strips > __GFP_RECLAIM when SLAB_ALLOC_NOLOCK is specified. > > When trylock fails or the kernel observes non-NULL pcs->rcu_free after > lock acquisition, free the sheaf instead of putting it to the barn. > This is rare and not worth complicating the code. > > Since call_rcu() cannot be called in an unknown context, > kfree_rcu_sheaf() fails when the rcu sheaf becomes full. > > Link: > https://lore.kernel.org/linux-mm/[email protected] > Signed-off-by: Harry Yoo (Oracle) <[email protected]>
LGTM. Reviewed-by: Vlastimil Babka (SUSE) <[email protected]> Nits below: > --- > mm/slab.h | 18 +++++++++++++++++- > mm/slab_common.c | 2 +- > mm/slub.c | 36 ++++++++++++++++++++++++++++-------- > 3 files changed, 46 insertions(+), 10 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 281a65233795..85ef2ebc9812 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -23,11 +23,27 @@ > #define SLAB_ALLOC_NEW_SLAB 0x02 /* a flag for alloc_slab_obj_exts() */ > #define SLAB_ALLOC_NO_RECURSE 0x04 /* prevent kmalloc() recursion */ > > +#define SLAB_FREE_DEFAULT 0x00 /* no flags */ > +#define SLAB_FREE_NOLOCK 0x01 /* spinning not allowed */ > + > +static inline unsigned int to_alloc_flags(unsigned int free_flags) > +{ > + if (free_flags & SLAB_FREE_NOLOCK) > + return SLAB_ALLOC_NOLOCK; > + else > + return SLAB_ALLOC_DEFAULT; > +} > + > static inline bool alloc_flags_allow_spinning(const unsigned int alloc_flags) > { > return !(alloc_flags & SLAB_ALLOC_NOLOCK); > } > > +static inline bool free_flags_allow_spinning(const unsigned int free_flags) > +{ > + return !(free_flags & SLAB_FREE_NOLOCK); > +} > + > void *__kmalloc_flags_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t flags, > unsigned int alloc_flags, int node) > __assume_kmalloc_alignment __alloc_size(1); > @@ -429,7 +445,7 @@ static inline bool is_kmalloc_normal(struct kmem_cache *s) > return !(s->flags & (SLAB_CACHE_DMA|SLAB_ACCOUNT|SLAB_RECLAIM_ACCOUNT)); > } > > -bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj); > +bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj, unsigned int > free_flags); > void flush_all_rcu_sheaves(void); > void flush_rcu_sheaves_on_cache(struct kmem_cache *s); > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index b6426d7ceec9..e07b4e6d6679 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1605,7 +1605,7 @@ static bool kfree_rcu_sheaf(void *obj) > > s = slab->slab_cache; > if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())) > - return __kfree_rcu_sheaf(s, obj); > + return __kfree_rcu_sheaf(s, obj, SLAB_FREE_DEFAULT); > > return false; > } > diff --git a/mm/slub.c b/mm/slub.c > index e32a68677537..0c350274fbff 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2814,10 +2814,14 @@ static inline struct slab_sheaf > *alloc_empty_sheaf(struct kmem_cache *s, > > gfp &= ~OBJCGS_CLEAR_MASK; > > + if (alloc_flags & SLAB_ALLOC_NOLOCK) > + gfp &= ~__GFP_RECLAIM; So in general we expect gfp and alloc flags to be compatible and warn if they are not. This now performs an auto-adjustment, which makes it unusual. But AFAICS only one caller relies on it - __kfree_rcu_sheaf(). So maybe we could just do it there? > + > return __alloc_empty_sheaf(s, gfp, alloc_flags, s->sheaf_capacity); > } > > -static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf) > +static void __free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf > *sheaf, > + bool allow_spin) Why not free_flags instead of allow_spin? Since you already introduced them. > { > /* > * If the sheaf was created with SLAB_ALLOC_NO_RECURSE flag then its > @@ -2829,11 +2833,20 @@ static void free_empty_sheaf(struct kmem_cache *s, > struct slab_sheaf *sheaf) > mark_obj_codetag_empty(sheaf); > > VM_WARN_ON_ONCE(sheaf->size > 0); > - kfree(sheaf); > + > + if (likely(allow_spin)) > + kfree(sheaf); > + else > + kfree_nolock(sheaf); > > stat(s, SHEAF_FREE); > } > > +static void free_empty_sheaf(struct kmem_cache *s, struct slab_sheaf *sheaf) > +{ > + __free_empty_sheaf(s, sheaf, /* allow_spin = */ true); Would avoid this ugliness. > +} > + > static unsigned int > refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min, > unsigned int max);
