linux-kernel - Re: [PATCH V6 8/9] mm/slab: move [__]ksize and slab

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Message-ID: <aWZDDfq72XP3Uuef@hyeyoo>
Date: Tue, 13 Jan 2026 22:05:17 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: akpm@...ux-foundation.org, andreyknvl@...il.com, cl@...two.org,
        dvyukov@...gle.com, glider@...gle.com, hannes@...xchg.org,
        linux-mm@...ck.org, mhocko@...nel.org, muchun.song@...ux.dev,
        rientjes@...gle.com, roman.gushchin@...ux.dev, ryabinin.a.a@...il.com,
        shakeel.butt@...ux.dev, surenb@...gle.com, vincenzo.frascino@....com,
        yeoreum.yun@....com, tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, hao.li@...ux.dev
Subject: Re: [PATCH V6 8/9] mm/slab: move [__]ksize and slab_ksize() to
 mm/slub.c

On Tue, Jan 13, 2026 at 01:44:45PM +0100, Vlastimil Babka wrote:
> On 1/13/26 7:18 AM, Harry Yoo wrote:
> > To access SLUB's internal implementation details beyond cache flags in
> > ksize(), move __ksize(), ksize(), and slab_ksize() to mm/slub.c.
> > 
> > Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
> > ---
> >  mm/slab.h        | 25 --------------
> >  mm/slab_common.c | 61 ----------------------------------
> >  mm/slub.c        | 86 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 86 insertions(+), 86 deletions(-)
> > 
> > diff --git a/mm/slab.h b/mm/slab.h
> > index 5176c762ec7c..957586d68b3c 100644
> > --- a/mm/slab.h
> > +++ b/mm/slab.h
> > @@ -665,31 +665,6 @@ void kvfree_rcu_cb(struct rcu_head *head);
> >  
> >  size_t __ksize(const void *objp);
> >  
> > -static inline size_t slab_ksize(const struct kmem_cache *s)
> > -{
> > -#ifdef CONFIG_SLUB_DEBUG
> > -	/*
> > -	 * Debugging requires use of the padding between object
> > -	 * and whatever may come after it.
> > -	 */
> > -	if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
> > -		return s->object_size;
> > -#endif
> > -	if (s->flags & SLAB_KASAN)
> > -		return s->object_size;
> > -	/*
> > -	 * If we have the need to store the freelist pointer
> > -	 * back there or track user information then we can
> > -	 * only use the space before that information.
> > -	 */
> > -	if (s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_STORE_USER))
> > -		return s->inuse;
> > -	/*
> > -	 * Else we can use all the padding etc for the allocation
> > -	 */
> > -	return s->size;
> > -}
> > -
> >  static inline unsigned int large_kmalloc_order(const struct page *page)
> >  {
> >  	return page[1].flags.f & 0xff;
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index c4cf9ed2ec92..aed91fd6fd10 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -983,43 +983,6 @@ void __init create_kmalloc_caches(void)
> >  						       0, SLAB_NO_MERGE, NULL);
> >  }
> >  
> > -/**
> > - * __ksize -- Report full size of underlying allocation
> > - * @object: pointer to the object
> > - *
> > - * This should only be used internally to query the true size of allocations.
> > - * It is not meant to be a way to discover the usable size of an allocation
> > - * after the fact. Instead, use kmalloc_size_roundup(). Using memory beyond
> > - * the originally requested allocation size may trigger KASAN, UBSAN_BOUNDS,
> > - * and/or FORTIFY_SOURCE.
> > - *
> > - * Return: size of the actual memory used by @object in bytes
> > - */
> > -size_t __ksize(const void *object)
> 
> Think it could be also static and not in slab.h? I'll make that change
> locally.

Uh, great. Thanks!

By the way `size_t __ksize(const void *objp);` is in both
include/linux/slab.h and mm/slab.h.

-- 
Cheers,
Harry / Hyeonggon