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[18.181.137.102]) by smtp.gmail.com with ESMTPSA id v10-20020a056a00148a00b004e0f420dd90sm4900007pfu.40.2022.03.03.22.34.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Mar 2022 22:34:55 -0800 (PST) From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: linux-mm@kvack.org Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Marco Elver , Matthew WilCox , Roman Gushchin , linux-kernel@vger.kernel.org, 42.hyeyoo@gmail.com Subject: [PATCH v2 5/5] mm/slub: refactor deactivate_slab() Date: Fri, 4 Mar 2022 06:34:27 +0000 Message-Id: <20220304063427.372145-6-42.hyeyoo@gmail.com> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20220304063427.372145-1-42.hyeyoo@gmail.com> References: <20220304063427.372145-1-42.hyeyoo@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Simplify deactivate_slab() by unlocking n->list_lock and retrying cmpxchg_double() when cmpxchg_double() fails, and perform add_{partial,full} only when it succeed. Releasing and taking n->list_lock again here is not harmful as SLUB avoids deactivating slabs as much as possible. [ vbabka@suse.cz: perform add_{partial,full} when cmpxchg_double() succeed. ] Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> --- mm/slub.c | 81 ++++++++++++++++++++++--------------------------------- 1 file changed, 32 insertions(+), 49 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index f9ae983a3dc6..c1a693ec5874 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2344,8 +2344,8 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab, { enum slab_modes { M_NONE, M_PARTIAL, M_FULL, M_FREE }; struct kmem_cache_node *n = get_node(s, slab_nid(slab)); - int lock = 0, free_delta = 0; - enum slab_modes l = M_NONE, m = M_NONE; + int free_delta = 0; + enum slab_modes mode = M_NONE; void *nextfree, *freelist_iter, *freelist_tail; int tail = DEACTIVATE_TO_HEAD; unsigned long flags = 0; @@ -2387,14 +2387,10 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab, * Ensure that the slab is unfrozen while the list presence * reflects the actual number of objects during unfreeze. * - * We setup the list membership and then perform a cmpxchg - * with the count. If there is a mismatch then the slab - * is not unfrozen but the slab is on the wrong list. - * - * Then we restart the process which may have to remove - * the slab from the list that we just put it on again - * because the number of objects in the slab may have - * changed. + * We first perform cmpxchg holding lock and insert to list + * when it succeed. If there is mismatch then slub is not + * unfrozen and number of objects in the slab may have changed. + * Then release lock and retry cmpxchg again. */ redo: @@ -2414,57 +2410,44 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab, new.frozen = 0; if (!new.inuse && n->nr_partial >= s->min_partial) - m = M_FREE; + mode = M_FREE; else if (new.freelist) { - m = M_PARTIAL; - if (!lock) { - lock = 1; - /* - * Taking the spinlock removes the possibility that - * acquire_slab() will see a slab that is frozen - */ - spin_lock_irqsave(&n->list_lock, flags); - } - } else { - m = M_FULL; - if (kmem_cache_debug_flags(s, SLAB_STORE_USER) && !lock) { - lock = 1; - /* - * This also ensures that the scanning of full - * slabs from diagnostic functions will not see - * any frozen slabs. - */ - spin_lock_irqsave(&n->list_lock, flags); - } + mode = M_PARTIAL; + /* + * Taking the spinlock removes the possibility that + * acquire_slab() will see a slab that is frozen + */ + spin_lock_irqsave(&n->list_lock, flags); + } else if (kmem_cache_debug_flags(s, SLAB_STORE_USER)) { + mode = M_FULL; + /* + * This also ensures that the scanning of full + * slabs from diagnostic functions will not see + * any frozen slabs. + */ + spin_lock_irqsave(&n->list_lock, flags); } - if (l != m) { - if (l == M_PARTIAL) - remove_partial(n, slab); - else if (l == M_FULL) - remove_full(s, n, slab); - - if (m == M_PARTIAL) - add_partial(n, slab, tail); - else if (m == M_FULL) - add_full(s, n, slab); - } - l = m; if (!cmpxchg_double_slab(s, slab, old.freelist, old.counters, new.freelist, new.counters, - "unfreezing slab")) + "unfreezing slab")) { + if (mode == M_PARTIAL || mode == M_FULL) + spin_unlock_irqrestore(&n->list_lock, flags); goto redo; + } - if (lock) - spin_unlock_irqrestore(&n->list_lock, flags); - if (m == M_PARTIAL) + if (mode == M_PARTIAL) { + add_partial(n, slab, tail); + spin_unlock_irqrestore(&n->list_lock, flags); stat(s, tail); - else if (m == M_FULL) + } else if (mode == M_FULL) { + add_full(s, n, slab); + spin_unlock_irqrestore(&n->list_lock, flags); stat(s, DEACTIVATE_FULL); - else if (m == M_FREE) { + } else if (mode == M_FREE) { stat(s, DEACTIVATE_EMPTY); discard_slab(s, slab); stat(s, FREE_SLAB); -- 2.33.1