[PATCH RFC 00/15] mm/slab: introduce alloc_flags and slab_alloc_context

[Vlastimil Babka (SUSE)]

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.

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;
};

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) <vbabka@xxxxxxxxxx>
---
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) <vbabka@xxxxxxxxxx>