kernel/linux.git/include/linux/slab.h, branch v7.0-rc7

mm/slub: drop duplicate kernel-doc for ksize()

2026-02-26T16:30:32+00:00

The implementation of ksize() was updated with kernel-doc by commit fab0694646d7 ("mm/slab: move [__]ksize and slab_ksize() to mm/slub.c") However, the public header still contains a kernel-doc comment attached to the ksize() prototype. Having documentation both in the header and next to the implementation causes Sphinx to treat the function as being documented twice, resulting in the warning: WARNING: Duplicate C declaration, also defined at core-api/mm-api:521 Declaration is '.. c:function:: size_t ksize(const void *objp)' Kernel-doc guidelines recommend keeping the documentation with the function implementation. Therefore remove the redundant kernel-doc block from include/linux/slab.h so that the implementation in slub.c remains the canonical source for documentation. No functional change. Fixes: fab0694646d7 ("mm/slab: move [__]ksize and slab_ksize() to mm/slub.c") Signed-off-by: Sanjay Chitroda Link: https://patch.msgid.link/20260226054712.3610744-1-sanjayembedded@gmail.com Signed-off-by: Vlastimil Babka (SUSE)

add default_gfp() helper macro and use it in the new *alloc_obj() helpers

2026-02-22T01:09:50+00:00

Most simple allocations use GFP_KERNEL, and with the new allocation helpers being introduced, let's just take advantage of that to simplify that default case. It's a numbers game: git grep 'alloc_obj(' | sed 's/.*\(GFP_[_A-Z]*\).*/\1/' | sort | uniq -c | sort -n | tail shows that about 90% of all those new allocator instances just use that standard GFP_KERNEL. Those helpers are already macros, and we can easily just make it be the default case when the gfp argument is missing. And yes, we could do that for all the legacy interfaces too, but let's keep it to just the new ones at least for now, since those all got converted recently anyway, so this is not any "extra" noise outside of that limited conversion. And, in fact, I want to do this before doing the -rc1 release, exactly so that we don't get extra merge conflicts. Signed-off-by: Linus Torvalds

slab.h: disable completely broken overflow handling in flex allocations

2026-02-21T23:12:09+00:00

Commit 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types") started using the new allocation helpers, and in the process showed that they were completely non-working. The overflow logic in overflows_flex_counter_type() is completely the wrong way around, and that broke __alloc_flex() completely. By chance, the resulting code was then such a mess that clang generated sufficiently garbage code that objtool warned about it all. Which made it somewhat quicker to narrow things down. While fixing overflows_flex_counter_type() would presumably fix this all, I'm excising the whole broken overflow logic from __alloc_flex(), because we don't want that kind of code in basic allocation functions anyway. That (no longer) broken overflows_flex_counter_type() thing needs to be inserted into the actual __set_flex_counter() logic in the unlikely case that we ever want this at all. And made conditional. Fixes: 81cee9166a90 ("compiler_types: Introduce __flex_counter() and family") Fixes: 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types") Cc: Kees Cook Link: https://lore.kernel.org/all/CAHk-=whEd020BYzGTzYrENjD9Z5_82xx6h8HsQvH5xDSnv0=Hw@mail.gmail.com/ Signed-off-by: Linus Torvalds

Merge tag 'slab-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab

2026-02-11T22:12:50+00:00

Pull slab updates from Vlastimil Babka: - The percpu sheaves caching layer was introduced as opt-in in 6.18 and now we enable it for all caches and remove the previous cpu (partial) slab caching mechanism. Besides the lower locking overhead and much more likely fastpath when freeing, this removes the rather complicated code related to the cpu slab lockless fastpaths (using this_cpu_try_cmpxchg128/64) and all its complications for PREEMPT_RT or kmalloc_nolock(). The lockless slab freelist+counters update operation using try_cmpxchg128/64 remains and is crucial for freeing remote NUMA objects, and to allow flushing objects from sheaves to slabs mostly without the node list_lock (Vlastimil Babka) - Eliminate slabobj_ext metadata overhead when possible. Instead of using kmalloc() to allocate the array for memcg and/or allocation profiling tag pointers, use leftover space in a slab or per-object padding due to alignment (Harry Yoo) - Various followup improvements to the above (Hao Li) * tag 'slab-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab: (39 commits) slub: let need_slab_obj_exts() return false if SLAB_NO_OBJ_EXT is set mm/slab: only allow SLAB_OBJ_EXT_IN_OBJ for unmergeable caches mm/slab: place slabobj_ext metadata in unused space within s->size mm/slab: move [__]ksize and slab_ksize() to mm/slub.c mm/slab: save memory by allocating slabobj_ext array from leftover mm/memcontrol,alloc_tag: handle slabobj_ext access under KASAN poison mm/slab: use stride to access slabobj_ext mm/slab: abstract slabobj_ext access via new slab_obj_ext() helper ext4: specify the free pointer offset for ext4_inode_cache mm/slab: allow specifying free pointer offset when using constructor mm/slab: use unsigned long for orig_size to ensure proper metadata align slub: clarify object field layout comments mm/slab: avoid allocating slabobj_ext array from its own slab slub: avoid list_lock contention from __refill_objects_any() mm/slub: cleanup and repurpose some stat items mm/slub: remove DEACTIVATE_TO_* stat items slab: remove frozen slab checks from __slab_free() slab: update overview comments slab: refill sheaves from all nodes slab: remove unused PREEMPT_RT specific macros ...

Merge branch 'slab/for-7.0/sheaves' into slab/for-next

2026-02-10T08:10:00+00:00

Merge series "slab: replace cpu (partial) slabs with sheaves". The percpu sheaves caching layer was introduced as opt-in but the goal was to eventually move all caches to them. This is the next step, enabling sheaves for all caches (except the two bootstrap ones) and then removing the per cpu (partial) slabs and lots of associated code. Besides the lower locking overhead and much more likely fastpath when freeing, this removes the rather complicated code related to the cpu slab lockless fastpaths (using this_cpu_try_cmpxchg128/64) and all its complications for PREEMPT_RT or kmalloc_nolock(). The lockless slab freelist+counters update operation using try_cmpxchg128/64 remains and is crucial for freeing remote NUMA objects and to allow flushing objects from sheaves to slabs mostly without the node list_lock. Link: https://lore.kernel.org/all/20260123-sheaves-for-all-v4-0-041323d506f7@suse.cz/

mm/slab: place slabobj_ext metadata in unused space within s->size

2026-02-04T09:05:36+00:00

When a cache has high s->align value and s->object_size is not aligned to it, each object ends up with some unused space because of alignment. If this wasted space is big enough, we can use it to store the slabobj_ext metadata instead of wasting it. On my system, this happens with caches like kmem_cache, mm_struct, pid, task_struct, sighand_cache, xfs_inode, and others. To place the slabobj_ext metadata within each object, the existing slab_obj_ext() logic can still be used by setting: - slab->obj_exts = slab_address(slab) + (slabobj_ext offset) - stride = s->size slab_obj_ext() doesn't need know where the metadata is stored, so this method works without adding extra overhead to slab_obj_ext(). A good example benefiting from this optimization is xfs_inode (object_size: 992, align: 64). To measure memory savings, 2 millions of files were created on XFS. [ MEMCG=y, MEM_ALLOC_PROFILING=n ] Before patch (creating ~2.64M directories on xfs): Slab: 5175976 kB SReclaimable: 3837524 kB SUnreclaim: 1338452 kB After patch (creating ~2.64M directories on xfs): Slab: 5152912 kB SReclaimable: 3838568 kB SUnreclaim: 1314344 kB (-23.54 MiB) Enjoy the memory savings! Suggested-by: Vlastimil Babka Signed-off-by: Harry Yoo Link: https://patch.msgid.link/20260113061845.159790-10-harry.yoo@oracle.com Signed-off-by: Vlastimil Babka

mm/slab: move [__]ksize and slab_ksize() to mm/slub.c

2026-02-04T09:05:35+00:00

To access SLUB's internal implementation details beyond cache flags in ksize(), move __ksize(), ksize(), and slab_ksize() to mm/slub.c. [vbabka@suse.cz: also make __ksize() static and move its kerneldoc to ksize() ] Signed-off-by: Harry Yoo Link: https://patch.msgid.link/20260113061845.159790-9-harry.yoo@oracle.com Signed-off-by: Vlastimil Babka

mm/slab: allow specifying free pointer offset when using constructor

2026-02-04T09:05:35+00:00

When a slab cache has a constructor, the free pointer is placed after the object because certain fields must not be overwritten even after the object is freed. However, some fields that the constructor does not initialize can safely be overwritten after free. Allow specifying the free pointer offset within the object, reducing the overall object size when some fields can be reused for the free pointer. Adjust the document accordingly. Signed-off-by: Harry Yoo Link: https://patch.msgid.link/20260113061845.159790-3-harry.yoo@oracle.com Signed-off-by: Vlastimil Babka

slab: add sheaves to most caches

2026-01-29T08:17:28+00:00

In the first step to replace cpu (partial) slabs with sheaves, enable sheaves for almost all caches. Treat args->sheaf_capacity as a minimum, and calculate sheaf capacity with a formula that roughly follows the formula for number of objects in cpu partial slabs in set_cpu_partial(). This should achieve roughly similar contention on the barn spin lock as there's currently for node list_lock without sheaves, to make benchmarking results comparable. It can be further tuned later. Don't enable sheaves for bootstrap caches as that wouldn't work. In order to recognize them by SLAB_NO_OBJ_EXT, make sure the flag exists even for !CONFIG_SLAB_OBJ_EXT. This limitation will be lifted for kmalloc caches after the necessary bootstrapping changes. Also do not enable sheaves for SLAB_NOLEAKTRACE caches to avoid recursion with kmemleak tracking (thanks to Breno Leitao). Reviewed-by: Suren Baghdasaryan Reviewed-by: Harry Yoo Reviewed-by: Hao Li Tested-by: Breno Leitao Reviewed-by: Liam R. Howlett Tested-by: Zhao Liu Signed-off-by: Vlastimil Babka

slab: Introduce kmalloc_flex() and family

2026-01-14T22:43:01+00:00

As done for kmalloc_obj*(), introduce a type-aware allocator for flexible arrays, which may also have "counted_by" annotations: ptr = kmalloc(struct_size(ptr, flex_member, count), gfp); becomes: ptr = kmalloc_flex(*ptr, flex_member, count, gfp); The internal use of __flex_counter() allows for automatically setting the counter member of a struct's flexible array member when it has been annotated with __counted_by(), avoiding any missed early size initializations while __counted_by() annotations are added to the kernel. Additionally, this also checks for "too large" allocations based on the type size of the counter variable. For example: if (count > type_max(ptr->flex_counter)) fail...; size = struct_size(ptr, flex_member, count); ptr = kmalloc(size, gfp); if (!ptr) fail...; ptr->flex_counter = count; becomes (n.b. unchanged from earlier example): ptr = kmalloc_flex(*ptr, flex_member, count, gfp); if (!ptr) fail...; ptr->flex_counter = count; Note that manual initialization of the flexible array counter is still required (at some point) after allocation as not all compiler versions support the __counted_by annotation yet. But doing it internally makes sure they cannot be missed when __counted_by _is_ available, meaning that the bounds checker will not trip due to the lack of "early enough" initializations that used to work before enabling the stricter bounds checking. For example: ptr = kmalloc_flex(*ptr, flex_member, count, gfp); fill(ptr->flex, count); ptr->flex_count = count; This works correctly before adding a __counted_by annotation (since nothing is checking ptr->flex accesses against ptr->flex_count). After adding the annotation, the bounds sanitizer would trip during fill() because ptr->flex_count wasn't set yet. But with kmalloc_flex() setting ptr->flex_count internally at allocation time, the existing code works without needing to move the ptr->flex_count assignment before the call to fill(). (This has been a stumbling block for __counted_by adoption.) Link: https://patch.msgid.link/20251203233036.3212363-4-kees@kernel.org Acked-by: Vlastimil Babka Signed-off-by: Kees Cook