Re: improve the kmem_cache_alloc_bulk API

On 5/27/26 14:21, Christoph Hellwig wrote:
> On Wed, May 27, 2026 at 11:11:31AM +0200, Vlastimil Babka (SUSE) wrote:
>> > value convention.  Fix that and add documentation.
>> > 
>> > Note that the few comments explaining it mention that the gfp flags
>> > must allow "spinning".  That's not really a term used in the memory
>> > allocator, is this supposed to mean "block" or "sleep"?
>> 
>> Page allocator now has alloc_pages_nolock() for when no spinning is
>> possible, and it uses ALLOC_TRYLOCK internally.
>> 
>> Slab has kmalloc_nolock() relying on that when it needs new pages.
> 
> The comment long predates that, and it isn't expressed using gfp flags,

Do we both mean this comment?

-/* Note that interrupts must be enabled when calling this function. */
+/*
+ * Note that interrupts must be enabled when calling this function and gfp     
+ * flags must allow spinning.               
+ */
 int kmem_cache_alloc_bulk_noprof(struct kmem_cache *s, gfp_t flags, size_t size,                                                                                                                                                    
                                 void **p)   

commit 46dea1744498 ("slab: refill sheaves from all nodes") from this January.
Previously it was just interrupts enabled.

> but by requiring separate functions so I somehow doubt that was meant.

Yeah, it's expressed by the _nolock variants. But slab propagates it internally
by the gfp flags, and since 46dea1744498 it affects kmem_cache_alloc_bulk().

> But I could also not see why it would not support GFP_ATOMIC /
> GFP_NOWAIT allocation, so I might just be confused.

Yeah those are supported because they can spin, just not sleep.