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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 21/21] mm/slub: cleanup and repurpose some stat items Message-ID: <5rmxfyxuhloucetufg2qic5elgi6frd7onjzdsosmhtjdqglij@5htmiqrdhkoj> References: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> <20260116-sheaves-for-all-v3-21-5595cb000772@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260116-sheaves-for-all-v3-21-5595cb000772@suse.cz> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C85A140007 X-Stat-Signature: w7onycnz3oouda5kwnhjis4s58o7uknh X-Rspam-User: X-HE-Tag: 1769061180-640891 X-HE-Meta: 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 39SAh/1j CrnZ/0DseatC+FPoKKR+nsCG7cm5tbfCWQjFfJYSK2UiBtM8LLhzfIQSCuKVmjv5gns2uzsgC/h625UMdphvSUII25axY8CL8fsDXuSEEMmLvOiKwMZSgDlEqp8/Tc9xYpk3wOHn3FlhHUtcM42uoUDWOqvk/3qjZmMYW20YzZEbh9sGFxNEURJxFWQ90NStcWoqh1dYqEjRW+xsPZe3Hqdnhw49y/J7hOvLJFDtMyarEuxo= 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 03:40:41PM +0100, Vlastimil Babka wrote: > A number of stat items related to cpu slabs became unused, remove them. > > Two of those were ALLOC_FASTPATH and FREE_FASTPATH. But instead of > removing those, use them instead of ALLOC_PCS and FREE_PCS, since > sheaves are the new (and only) fastpaths, Remove the recently added > _PCS variants instead. > > Change where FREE_SLOWPATH is counted so that it only counts freeing of > objects by slab users that (for whatever reason) do not go to a percpu > sheaf, and not all (including internal) callers of __slab_free(). Thus > flushing sheaves (counted by SHEAF_FLUSH) no longer also increments > FREE_SLOWPATH. This matches how ALLOC_SLOWPATH doesn't count sheaf > refills (counted by SHEAF_REFILL). > > Reviewed-by: Suren Baghdasaryan > Signed-off-by: Vlastimil Babka > --- > mm/slub.c | 77 +++++++++++++++++---------------------------------------------- > 1 file changed, 21 insertions(+), 56 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index c12e90cb2fca..d73ad44fa046 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -330,33 +330,19 @@ enum add_mode { > }; > > enum stat_item { > - ALLOC_PCS, /* Allocation from percpu sheaf */ > - ALLOC_FASTPATH, /* Allocation from cpu slab */ > - ALLOC_SLOWPATH, /* Allocation by getting a new cpu slab */ > - FREE_PCS, /* Free to percpu sheaf */ > + ALLOC_FASTPATH, /* Allocation from percpu sheaves */ > + ALLOC_SLOWPATH, /* Allocation from partial or new slab */ > FREE_RCU_SHEAF, /* Free to rcu_free sheaf */ > FREE_RCU_SHEAF_FAIL, /* Failed to free to a rcu_free sheaf */ > - FREE_FASTPATH, /* Free to cpu slab */ > - FREE_SLOWPATH, /* Freeing not to cpu slab */ > + FREE_FASTPATH, /* Free to percpu sheaves */ > + FREE_SLOWPATH, /* Free to a slab */ Nits: Would it make sense to add stat(s, FREE_SLOWPATH) in free_deferred_objects() as well, since it also calls __slab_free()? Everything else looks good. This patchset replaces cpu slab with cpu sheaves and really simplifies the code overall - I really like the direction and the end result. It's really been a pleasure reviewing this series. Thanks! Reviewed-by: Hao Li -- Thanks, Hao > FREE_ADD_PARTIAL, /* Freeing moves slab to partial list */ > FREE_REMOVE_PARTIAL, /* Freeing removes last object */ > - ALLOC_FROM_PARTIAL, /* Cpu slab acquired from node partial list */ > - ALLOC_SLAB, /* Cpu slab acquired from page allocator */ > - ALLOC_REFILL, /* Refill cpu slab from slab freelist */ > - ALLOC_NODE_MISMATCH, /* Switching cpu slab */ > + ALLOC_SLAB, /* New slab acquired from page allocator */ > + ALLOC_NODE_MISMATCH, /* Requested node different from cpu sheaf */ > FREE_SLAB, /* Slab freed to the page allocator */ > - CPUSLAB_FLUSH, /* Abandoning of the cpu slab */ > - DEACTIVATE_FULL, /* Cpu slab was full when deactivated */ > - DEACTIVATE_EMPTY, /* Cpu slab was empty when deactivated */ > - DEACTIVATE_REMOTE_FREES,/* Slab contained remotely freed objects */ > - DEACTIVATE_BYPASS, /* Implicit deactivation */ > ORDER_FALLBACK, /* Number of times fallback was necessary */ > - CMPXCHG_DOUBLE_CPU_FAIL,/* Failures of this_cpu_cmpxchg_double */ > CMPXCHG_DOUBLE_FAIL, /* Failures of slab freelist update */ > - CPU_PARTIAL_ALLOC, /* Used cpu partial on alloc */ > - CPU_PARTIAL_FREE, /* Refill cpu partial on free */ > - CPU_PARTIAL_NODE, /* Refill cpu partial from node partial */ > - CPU_PARTIAL_DRAIN, /* Drain cpu partial to node partial */ > SHEAF_FLUSH, /* Objects flushed from a sheaf */ > SHEAF_REFILL, /* Objects refilled to a sheaf */ > SHEAF_ALLOC, /* Allocation of an empty sheaf */ > @@ -4347,8 +4333,10 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node) > * We assume the percpu sheaves contain only local objects although it's > * not completely guaranteed, so we verify later. > */ > - if (unlikely(node_requested && node != numa_mem_id())) > + if (unlikely(node_requested && node != numa_mem_id())) { > + stat(s, ALLOC_NODE_MISMATCH); > return NULL; > + } > > if (!local_trylock(&s->cpu_sheaves->lock)) > return NULL; > @@ -4371,6 +4359,7 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node) > */ > if (page_to_nid(virt_to_page(object)) != node) { > local_unlock(&s->cpu_sheaves->lock); > + stat(s, ALLOC_NODE_MISMATCH); > return NULL; > } > } > @@ -4379,7 +4368,7 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node) > > local_unlock(&s->cpu_sheaves->lock); > > - stat(s, ALLOC_PCS); > + stat(s, ALLOC_FASTPATH); > > return object; > } > @@ -4451,7 +4440,7 @@ unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, gfp_t gfp, size_t size, > > local_unlock(&s->cpu_sheaves->lock); > > - stat_add(s, ALLOC_PCS, batch); > + stat_add(s, ALLOC_FASTPATH, batch); > > allocated += batch; > > @@ -5111,8 +5100,6 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, > unsigned long flags; > bool on_node_partial; > > - stat(s, FREE_SLOWPATH); > - > if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) { > free_to_partial_list(s, slab, head, tail, cnt, addr); > return; > @@ -5416,7 +5403,7 @@ bool free_to_pcs(struct kmem_cache *s, void *object, bool allow_spin) > > local_unlock(&s->cpu_sheaves->lock); > > - stat(s, FREE_PCS); > + stat(s, FREE_FASTPATH); > > return true; > } > @@ -5664,7 +5651,7 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p) > > local_unlock(&s->cpu_sheaves->lock); > > - stat_add(s, FREE_PCS, batch); > + stat_add(s, FREE_FASTPATH, batch); > > if (batch < size) { > p += batch; > @@ -5686,10 +5673,12 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p) > */ > fallback: > __kmem_cache_free_bulk(s, size, p); > + stat_add(s, FREE_SLOWPATH, size); > > flush_remote: > if (remote_nr) { > __kmem_cache_free_bulk(s, remote_nr, &remote_objects[0]); > + stat_add(s, FREE_SLOWPATH, remote_nr); > if (i < size) { > remote_nr = 0; > goto next_remote_batch; > @@ -5784,6 +5773,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object, > } > > __slab_free(s, slab, object, object, 1, addr); > + stat(s, FREE_SLOWPATH); > } > > #ifdef CONFIG_MEMCG > @@ -5806,8 +5796,10 @@ void slab_free_bulk(struct kmem_cache *s, struct slab *slab, void *head, > * With KASAN enabled slab_free_freelist_hook modifies the freelist > * to remove objects, whose reuse must be delayed. > */ > - if (likely(slab_free_freelist_hook(s, &head, &tail, &cnt))) > + if (likely(slab_free_freelist_hook(s, &head, &tail, &cnt))) { > __slab_free(s, slab, head, tail, cnt, addr); > + stat_add(s, FREE_SLOWPATH, cnt); > + } > } > > #ifdef CONFIG_SLUB_RCU_DEBUG > @@ -6705,6 +6697,7 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, > i = refill_objects(s, p, flags, size, size); > if (i < size) > goto error; > + stat_add(s, ALLOC_SLOWPATH, i); > } > > return i; > @@ -8704,33 +8697,19 @@ static ssize_t text##_store(struct kmem_cache *s, \ > } \ > SLAB_ATTR(text); \ > > -STAT_ATTR(ALLOC_PCS, alloc_cpu_sheaf); > STAT_ATTR(ALLOC_FASTPATH, alloc_fastpath); > STAT_ATTR(ALLOC_SLOWPATH, alloc_slowpath); > -STAT_ATTR(FREE_PCS, free_cpu_sheaf); > STAT_ATTR(FREE_RCU_SHEAF, free_rcu_sheaf); > STAT_ATTR(FREE_RCU_SHEAF_FAIL, free_rcu_sheaf_fail); > STAT_ATTR(FREE_FASTPATH, free_fastpath); > STAT_ATTR(FREE_SLOWPATH, free_slowpath); > STAT_ATTR(FREE_ADD_PARTIAL, free_add_partial); > STAT_ATTR(FREE_REMOVE_PARTIAL, free_remove_partial); > -STAT_ATTR(ALLOC_FROM_PARTIAL, alloc_from_partial); > STAT_ATTR(ALLOC_SLAB, alloc_slab); > -STAT_ATTR(ALLOC_REFILL, alloc_refill); > STAT_ATTR(ALLOC_NODE_MISMATCH, alloc_node_mismatch); > STAT_ATTR(FREE_SLAB, free_slab); > -STAT_ATTR(CPUSLAB_FLUSH, cpuslab_flush); > -STAT_ATTR(DEACTIVATE_FULL, deactivate_full); > -STAT_ATTR(DEACTIVATE_EMPTY, deactivate_empty); > -STAT_ATTR(DEACTIVATE_REMOTE_FREES, deactivate_remote_frees); > -STAT_ATTR(DEACTIVATE_BYPASS, deactivate_bypass); > STAT_ATTR(ORDER_FALLBACK, order_fallback); > -STAT_ATTR(CMPXCHG_DOUBLE_CPU_FAIL, cmpxchg_double_cpu_fail); > STAT_ATTR(CMPXCHG_DOUBLE_FAIL, cmpxchg_double_fail); > -STAT_ATTR(CPU_PARTIAL_ALLOC, cpu_partial_alloc); > -STAT_ATTR(CPU_PARTIAL_FREE, cpu_partial_free); > -STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node); > -STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain); > STAT_ATTR(SHEAF_FLUSH, sheaf_flush); > STAT_ATTR(SHEAF_REFILL, sheaf_refill); > STAT_ATTR(SHEAF_ALLOC, sheaf_alloc); > @@ -8806,33 +8785,19 @@ static struct attribute *slab_attrs[] = { > &remote_node_defrag_ratio_attr.attr, > #endif > #ifdef CONFIG_SLUB_STATS > - &alloc_cpu_sheaf_attr.attr, > &alloc_fastpath_attr.attr, > &alloc_slowpath_attr.attr, > - &free_cpu_sheaf_attr.attr, > &free_rcu_sheaf_attr.attr, > &free_rcu_sheaf_fail_attr.attr, > &free_fastpath_attr.attr, > &free_slowpath_attr.attr, > &free_add_partial_attr.attr, > &free_remove_partial_attr.attr, > - &alloc_from_partial_attr.attr, > &alloc_slab_attr.attr, > - &alloc_refill_attr.attr, > &alloc_node_mismatch_attr.attr, > &free_slab_attr.attr, > - &cpuslab_flush_attr.attr, > - &deactivate_full_attr.attr, > - &deactivate_empty_attr.attr, > - &deactivate_remote_frees_attr.attr, > - &deactivate_bypass_attr.attr, > &order_fallback_attr.attr, > &cmpxchg_double_fail_attr.attr, > - &cmpxchg_double_cpu_fail_attr.attr, > - &cpu_partial_alloc_attr.attr, > - &cpu_partial_free_attr.attr, > - &cpu_partial_node_attr.attr, > - &cpu_partial_drain_attr.attr, > &sheaf_flush_attr.attr, > &sheaf_refill_attr.attr, > &sheaf_alloc_attr.attr, > > -- > 2.52.0 >