Re: [PATCH] slub: clarify kmem_cache_refill_sheaf() failure behavior

[Hao Li <hao.li@linux.dev>]

On Fri, Mar 13, 2026 at 09:36:22PM +0900, Harry Yoo wrote:
> On Thu, Mar 12, 2026 at 07:42:25PM +0800, Hao Li wrote:
> > kmem_cache_refill_sheaf() can fail in two slightly different ways.
> > During an in-place refill, some objects may already have been added
> > before the function returns -ENOMEM. On the other hand, if allocation of
> > a larger replacement sheaf fails, the original sheaf remains unchanged.
> > 
> > Update the comment to spell out both cases explicitly for clarity.
> > 
> > Signed-off-by: Hao Li <hao.li@linux.dev>
> > ---
> >
> >  mm/slub.c | 21 +++++++++++++++------
> >  1 file changed, 15 insertions(+), 6 deletions(-)
> > 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 11a99bd06ac7..8ae248b5b384 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -5005,14 +5005,23 @@ void kmem_cache_return_sheaf(struct kmem_cache *s, gfp_t gfp,
> >  }
> >  
> >  /*
> > - * refill a sheaf previously returned by kmem_cache_prefill_sheaf to at least
> > - * the given size
> > + * Refill a sheaf previously returned by kmem_cache_prefill_sheaf to at least
> > + * the given size.
> >   *
> > - * the sheaf might be replaced by a new one when requesting more than
> > - * s->sheaf_capacity objects if such replacement is necessary, but the refill
> > - * fails (returning -ENOMEM), the existing sheaf is left intact
> > + * On success, the sheaf will contain at least @size objects.
> >   *
> > - * In practice we always refill to full sheaf's capacity.
> > + * On failure, there are two cases:
> > + *
> > + *     1. If the requested size fits within the current sheaf's capacity, the
> > + *     refill is done in place. In that case, a failed refill may still fill
> > + *     some additional objects into the existing sheaf before returning -ENOMEM.
> > + *
> > + *     2. If the requested size exceeds the current sheaf's capacity, a new
> > + *     larger sheaf may be allocated to replace the original one. In that case,
> > + *     if allocation of the replacement sheaf fails, the original sheaf is left
> > + *     unchanged.
> 
> This is correct, but users of this API probably don't need to know the
> implementation in detail.
> 
> I think it's fine to simply say the sheaf may have additional objects even
> on failure?

That makes sense.
Too much explanation could actually distract users.
Thanks!

> 
> > + *
> > + * In practice we usually refill to the sheaf's full capacity.
> >   */
> >  int kmem_cache_refill_sheaf(struct kmem_cache *s, gfp_t gfp,
> >  			    struct slab_sheaf **sheafp, unsigned int size)
> > -- 
> > 2.50.1
> > 
> 
> -- 
> Cheers,
> Harry / Hyeonggon