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From: Hao Li To: Vlastimil Babka Cc: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH v3 09/21] slab: add optimized sheaf refill from partial list Message-ID: References: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> <20260116-sheaves-for-all-v3-9-5595cb000772@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260116-sheaves-for-all-v3-9-5595cb000772@suse.cz> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7AC8340004 X-Rspam-User: X-Stat-Signature: s5at5wzmjmx4bdxsh6ddimuzueonh4t1 X-HE-Tag: 1768877755-326412 X-HE-Meta: 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 8yiOTmIa lC2UgNWVO0a35aJcJVDJgaxXKCmRK9xrG7zfcN0pN6SMBXfJIFTEbSl/ewMrCNJPgCKmaxKbvcfI5Wxt1/VijV8oeCgAutDQSitwy7K2rF6ayss2L6GblEmj3VVVs+vchO6OjCKlblXzM7arwSGtaBoheRTFsT9ZhABBraj/lHkIiyKsbv8tZpemSsgG2yrcAuHhdB133WMUu7RA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 16, 2026 at 03:40:29PM +0100, Vlastimil Babka wrote: > At this point we have sheaves enabled for all caches, but their refill > is done via __kmem_cache_alloc_bulk() which relies on cpu (partial) > slabs - now a redundant caching layer that we are about to remove. > > The refill will thus be done from slabs on the node partial list. > Introduce new functions that can do that in an optimized way as it's > easier than modifying the __kmem_cache_alloc_bulk() call chain. > > Extend struct partial_context so it can return a list of slabs from the > partial list with the sum of free objects in them within the requested > min and max. > > Introduce get_partial_node_bulk() that removes the slabs from freelist > and returns them in the list. > > Introduce get_freelist_nofreeze() which grabs the freelist without > freezing the slab. > > Introduce alloc_from_new_slab() which can allocate multiple objects from > a newly allocated slab where we don't need to synchronize with freeing. > In some aspects it's similar to alloc_single_from_new_slab() but assumes > the cache is a non-debug one so it can avoid some actions. > > Introduce __refill_objects() that uses the functions above to fill an > array of objects. It has to handle the possibility that the slabs will > contain more objects that were requested, due to concurrent freeing of > objects to those slabs. When no more slabs on partial lists are > available, it will allocate new slabs. It is intended to be only used > in context where spinning is allowed, so add a WARN_ON_ONCE check there. > > Finally, switch refill_sheaf() to use __refill_objects(). Sheaves are > only refilled from contexts that allow spinning, or even blocking. > > Signed-off-by: Vlastimil Babka > --- > mm/slub.c | 284 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 264 insertions(+), 20 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 9bea8a65e510..dce80463f92c 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -246,6 +246,9 @@ struct partial_context { > gfp_t flags; > unsigned int orig_size; > void *object; > + unsigned int min_objects; > + unsigned int max_objects; > + struct list_head slabs; > }; > ... > +static unsigned int alloc_from_new_slab(struct kmem_cache *s, struct slab *slab, > + void **p, unsigned int count, bool allow_spin) > +{ > + unsigned int allocated = 0; > + struct kmem_cache_node *n; > + unsigned long flags; > + void *object; > + > + if (!allow_spin && (slab->objects - slab->inuse) > count) { I was wondering - given that slab->inuse is 0 for a newly allocated slab, is there a reason to use "slab->objects - slab->inuse" instead of simply slab->objects. > + > + n = get_node(s, slab_nid(slab)); > + > + if (!spin_trylock_irqsave(&n->list_lock, flags)) { > + /* Unlucky, discard newly allocated slab */ > + defer_deactivate_slab(slab, NULL); > + return 0; > + } > + } > + > + object = slab->freelist; > + while (object && allocated < count) { > + p[allocated] = object; > + object = get_freepointer(s, object); > + maybe_wipe_obj_freeptr(s, p[allocated]); > + > + slab->inuse++; > + allocated++; > + } > + slab->freelist = object; > + > + if (slab->freelist) { > + > + if (allow_spin) { > + n = get_node(s, slab_nid(slab)); > + spin_lock_irqsave(&n->list_lock, flags); > + } > + add_partial(n, slab, DEACTIVATE_TO_HEAD); > + spin_unlock_irqrestore(&n->list_lock, flags); > + } > + > + inc_slabs_node(s, slab_nid(slab), slab->objects); > + return allocated; > +} > + ...