__GFP_NO_OBJ_EXT has limited scope within the slab allocator itself and gfp flags are a scarce resource, unlike slab's alloc_flags. Introduce SLAB_ALLOC_NO_RECURSE alloc flag that has the same intent as __GFP_NO_OBJ_EXT but a more generic name, meaning that a kmalloc() family function should not recurse into another kmalloc*() for the purposes of allocating auxiliary structures (obj_ext arrays or sheaves). First, replace the __GFP_NO_OBJ_EXT for allocating obj_ext arrays in alloc_slab_obj_exts(). Make use of the newly added kmalloc_flags() function, where we can pass alloc_flags with SLAB_ALLOC_NO_RECURSE added. This will also pass through SLAB_ALLOC_NOLOCK so we don't need to special case kmalloc_nolock() anymore. Note that until now the kmalloc_nolock() ignored the incoming gfp flags and hardcoded __GFP_ZERO | __GFP_NO_OBJ_EXT. But it's correct to pass on the incoming gfp flags (only augmented with __GFP_ZERO), because if alloc_flags contain SLAB_ALLOC_NOLOCK, the incoming gfp flags have to be also compatible with it. However, we might have added __GFP_THISNODE for opportunistic slab allocation, as pointed out by Hao Li, and __GFP_COMP by allocate_slab() as pointed out by Shengming Hu. Solve this by adding both flags to OBJCGS_CLEAR_MASK as it makes sense to strip them anyway for non-kmalloc_nolock() allocations of sheaves or obj_ext arrays as well. To avoid recursion of sheaf -> obj_ext -> sheaf -> ... allocations at this patch, until the next patch converts sheaves to SLAB_ALLOC_NO_RECURSE, use both gfp and alloc_flags for obj_ext. The next patch will remove the gfp part. Link: https://patch.msgid.link/20260610-slab_alloc_flags-v2-15-7190909db118@kernel.org Signed-off-by: Vlastimil Babka (SUSE) --- mm/slab.h | 1 + mm/slub.c | 22 ++++++++++++---------- 2 files changed, 13 insertions(+), 10 deletions(-) diff --git a/mm/slab.h b/mm/slab.h index 482b8e0fe797..281a65233795 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -21,6 +21,7 @@ #define SLAB_ALLOC_DEFAULT 0x00 /* no flags */ #define SLAB_ALLOC_NOLOCK 0x01 /* a kmalloc_nolock() allocation */ #define SLAB_ALLOC_NEW_SLAB 0x02 /* a flag for alloc_slab_obj_exts() */ +#define SLAB_ALLOC_NO_RECURSE 0x04 /* prevent kmalloc() recursion */ static inline bool alloc_flags_allow_spinning(const unsigned int alloc_flags) { diff --git a/mm/slub.c b/mm/slub.c index 383d39a22561..fc5b8c85b690 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2047,12 +2047,16 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node, #endif /* CONFIG_SLUB_DEBUG */ /* - * The allocated objcg pointers array is not accounted directly. + * The allocated objcg pointers array or sheaf is not accounted directly. * Moreover, it should not come from DMA buffer and is not readily - * reclaimable. So those GFP bits should be masked off. + * reclaimable. Node restriction for the parent allocation also should + * not apply to the slab's internal objects, as well as __GFP_COMP used + * for new slab allocations. + * So those GFP bits should be masked off. */ #define OBJCGS_CLEAR_MASK (__GFP_DMA | __GFP_RECLAIMABLE | \ - __GFP_ACCOUNT | __GFP_NOFAIL) + __GFP_ACCOUNT | __GFP_NOFAIL | \ + __GFP_THISNODE | __GFP_COMP) #ifdef CONFIG_SLAB_OBJ_EXT @@ -2168,14 +2172,12 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, gfp &= ~OBJCGS_CLEAR_MASK; /* Prevent recursive extension vector allocation */ gfp |= __GFP_NO_OBJ_EXT; + alloc_flags |= SLAB_ALLOC_NO_RECURSE; sz = obj_exts_alloc_size(s, slab, gfp); - if (unlikely(!allow_spin)) - vec = kmalloc_nolock(sz, __GFP_ZERO | __GFP_NO_OBJ_EXT, - slab_nid(slab)); - else - vec = kmalloc_node(sz, gfp | __GFP_ZERO, slab_nid(slab)); + /* This will use kmalloc_nolock() if alloc_flags say so */ + vec = kmalloc_flags(sz, gfp | __GFP_ZERO, alloc_flags, slab_nid(slab)); if (!vec) { /* @@ -2251,7 +2253,7 @@ static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin) } /* - * obj_exts was created with __GFP_NO_OBJ_EXT flag, therefore its + * obj_exts was created with SLAB_ALLOC_NO_RECURSE flag, therefore its * corresponding extension will be NULL. alloc_tag_sub() will throw a * warning if slab has extensions but the extension of an object is * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that @@ -2374,7 +2376,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags, if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE)) return; - if (flags & __GFP_NO_OBJ_EXT) + if (alloc_flags & SLAB_ALLOC_NO_RECURSE || flags & __GFP_NO_OBJ_EXT) return; slab = virt_to_slab(object); -- 2.54.0