On 6/9/26 6:17 PM, Vlastimil Babka (SUSE) wrote: > This series is based on slab/for-next. If all goes well, it would > hopefully go to slab/for-next soon after the 7.2 merge window, so any > other work can be based on it to avoid conflicts, as it touches a lot > parts of slab. > > Git: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=b4/slab_alloc_flags > > The slab implementation currently relies on gfp flags to convey > some context information internally: > > - The absence of both __GFP_RECLAIM flags is interpreted as "cannot spin > on locks", and intended to be used by kmalloc_nolock(). But false > positives are possible e.g. during early boot where gfp_allowed_mask > clears __GFP_RECLAIM from all allocations. This leads to unnecessary > allocation failures and workarounds such as fd3634312a04 ("debugobject: > Make it work with deferred page initialization - again"). > > - __GFP_NO_OBJ_EXT exists and takes up valuable bit in the gfp flags > space, only to prevent recursive kmalloc() allocations for obj_ext > arrays and sheaves. [ Cc'ing Vishal and Matthew as it's somewhat relevant to memdescs... ] When the page allocator starts allocateing slab objects, we still need a way to avoid recursion for obj_ext arrays and sheaves (by passing SLAB_ALLOC_NO_RECURSE). Looking at kmalloc_flags(), probably we'll end up introducing a separate gfp type for slab-specific flags? Hmm but SLAB_ALLOC_* flags are defined in mm/slab.h and kmalloc_flags() is defined in include/linux/slab.h. Do yo intend to restrict the slab alloc flags to MM only? > The page allocator uses its internal alloc_flags to convey various > context information, including ALLOC_TRYLOCK (meaning "cannot spin"). > This series copies that concept for the slab allocator, with its own > slab-specific internal flags: > > - SLAB_ALLOC_DEFAULT - no extra flags (the value is 0), but explicit > - SLAB_ALLOC_TRYLOCK - do not spin on locks (used by kmalloc_nolock()) > - SLAB_ALLOC_NEW_SLAB - replacing existing 'bool new_slab' parameter > for allocating obj_ext arrays > - SLAB_ALLOC_NO_RECURSE - replacing usage of __GFP_NO_OBJ_EXT > > To reduce the amount of parameters in various internal functions, we > additionally introduce slab_alloc_context (also inspired by page > allocator's alloc_context) for passing a number of existing arguments > and the new alloc_flags: > > /* Structure holding extra parameters for slab allocations */ > struct slab_alloc_context { > unsigned long caller_addr; > unsigned long orig_size; > unsigned int alloc_flags; > struct list_lru *lru; > }; Perhaps beyond the scope of the patchset, but I wonder if we could have something like struct slab_alloc_context but for kmalloc callers to simplify {PASS,DECL}_KMALLOC_PARAMS(). Something like: struct kmalloc_params { #ifdef CONFIG_SLAB_BUCKETS kmem_buckets *b; #endif #ifdef CONFIG_KMALLOC_PARTITION_CACHES kmalloc_token_t token; #endif }; The idea is to move optional kmalloc parameters (depending on config) into a single struct, instead of using the macros. void *__kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller, struct kmalloc_params params); void *kmalloc_node() { /* ... snip ...*/ struct kmalloc_params params = KMALLOC_PARAMS(params.b, params.token); return __kmalloc_node(size, flags, node, _RET_IP_, params); } The compiler should optimize away unused fields based on the config. Per System V AMD64 ABI, the compiler will use registers to pass the struct, as long as the struct size does not exceed 16 bytes. (Otherwise it will be passed on stack). > This also replaces the existing struct partial_context. > > The last necessary piece is kmalloc_flags() which can take the > alloc_flags in addition to gfp flags and is intended for the recursive > allocations of sheaves and obj_ext arrays, so that both > SLAB_ALLOC_TRYLOCK and SLAB_ALLOC_NO_RECURSE can be communicated. > Internally it decides between kmalloc_nolock() and normal kmalloc() > depending SLAB_ALLOC_TRYLOCK. > > The rest of the series is gradually expanding the usage of both > alloc_flags and slab_alloc_context as necessary, with bits of > refactoring. Then, __GFP_NO_OBJ_EXT is removed completely. > > Note that some usage of gfpflags_allow_spinning() relying on absence of > __GFP_RECLAIM remains outside of slab (and page allocator) in memcg, > page_owner and stackdepot code. These can thus yield false-positive > decisions that spinning is not allowed, but should not result in > important allocations failing anymore. > > Signed-off-by: Vlastimil Babka (SUSE) > --- > Vlastimil Babka (SUSE) (15): > mm/slab: always zero only requested size on alloc > mm/slab: stop inlining __slab_alloc_node() > mm/slab: introduce slab_alloc_context > mm/slab: introduce alloc_flags and SLAB_ALLOC_TRYLOCK > mm/slab: add alloc_flags to slab_alloc_context > mm/slab: replace struct partial_context with slab_alloc_context > mm/slab: pass alloc_flags to new slab allocation > mm/slab: pass alloc_flags through slab_post_alloc_hook() chain > mm/slab: replace slab_alloc_node() parameters with slab_alloc_context > mm/slab: allow kmem_cache_alloc_bulk() with any gfp flags > mm/slab: pass slab_alloc_context to __do_kmalloc_node() > mm/slab: introduce kmalloc_flags() > mm/slab: remove __GFP_NO_OBJ_EXT usage from alloc_slab_obj_exts() > mm/slab: replace __GFP_NO_OBJ_EXT with SLAB_ALLOC_NO_RECURSE for sheaves > mm: remove the __GFP_NO_OBJ_EXT flag > > include/linux/gfp_types.h | 7 - > include/linux/slab.h | 14 +- > include/trace/events/mmflags.h | 10 +- > lib/alloc_tag.c | 2 +- > mm/kfence/core.c | 6 +- > mm/memcontrol.c | 5 +- > mm/slab.h | 16 +- > mm/slub.c | 423 ++++++++++++++++++++++++---------------- > tools/include/linux/gfp_types.h | 7 - > 9 files changed, 288 insertions(+), 202 deletions(-) > --- > base-commit: 500b2c9755301742bdbb61249511ac11a4665dae > change-id: 20260601-slab_alloc_flags-25c782b0c57c > > Best regards, > -- > Vlastimil Babka (SUSE) -- Cheers, Harry / Hyeonggon