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h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=y53X1OR0ou7ONoOuH7610a+3WZLZ1CUD0l8GYtsY+0s=; b=Lo/LT0DiTZ1tzIDy2t+5hGWl0a6Ln+BgPNA8f+HJyPS/qGGYoWlrDKv0MxdazJ0LPnuHDc fmi9rp4WwPy/rjBg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 878A213BE0; Mon, 23 Aug 2021 14:58:43 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 8CeVIKO3I2EFQQAAMHmgww (envelope-from ); Mon, 23 Aug 2021 14:58:43 +0000 From: Vlastimil Babka To: Andrew Morton , Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Galbraith , Sebastian Andrzej Siewior , Thomas Gleixner , Mel Gorman , Jesper Dangaard Brouer , Jann Horn , Vlastimil Babka Subject: [PATCH v5 34/35] mm, slub: use migrate_disable() on PREEMPT_RT Date: Mon, 23 Aug 2021 16:58:25 +0200 Message-Id: <20210823145826.3857-35-vbabka@suse.cz> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210823145826.3857-1-vbabka@suse.cz> References: <20210823145826.3857-1-vbabka@suse.cz> MIME-Version: 1.0 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=oXulej8N; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="Lo/LT0Di"; spf=pass (imf17.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Stat-Signature: b839gs67i45nzhkm9a66cc6fa4obicbd X-Rspamd-Queue-Id: AB143F00039C X-Rspamd-Server: rspam04 X-HE-Tag: 1629730724-14598 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: We currently use preempt_disable() (directly or via get_cpu_ptr()) to stabilize the pointer to kmem_cache_cpu. On PREEMPT_RT this would be incompatible with the list_lock spinlock. We can use migrate_disable() instead, but that increases overhead on !PREEMPT_RT as it's an unconditional function call. In order to get the best available mechanism on both PREEMPT_RT and !PREEMPT_RT, introduce private slub_get_cpu_ptr() and slub_put_cpu_ptr() wrappers and use them. Signed-off-by: Vlastimil Babka --- mm/slub.c | 39 ++++++++++++++++++++++++++++++--------- 1 file changed, 30 insertions(+), 9 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 2362efab53df..cd78b7844273 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -118,6 +118,26 @@ * the fast path and disables lockless freelists. */ +/* + * We could simply use migrate_disable()/enable() but as long as it's a + * function call even on !PREEMPT_RT, use inline preempt_disable() there. + */ +#ifndef CONFIG_PREEMPT_RT +#define slub_get_cpu_ptr(var) get_cpu_ptr(var) +#define slub_put_cpu_ptr(var) put_cpu_ptr(var) +#else +#define slub_get_cpu_ptr(var) \ +({ \ + migrate_disable(); \ + this_cpu_ptr(var); \ +}) +#define slub_put_cpu_ptr(var) \ +do { \ + (void)(var); \ + migrate_enable(); \ +} while (0) +#endif + #ifdef CONFIG_SLUB_DEBUG #ifdef CONFIG_SLUB_DEBUG_ON DEFINE_STATIC_KEY_TRUE(slub_debug_enabled); @@ -2828,7 +2848,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, if (unlikely(!pfmemalloc_match_unsafe(page, gfpflags))) goto deactivate_slab; - /* must check again c->page in case IRQ handler changed it */ + /* must check again c->page in case we got preempted and it changed */ local_irq_save(flags); if (unlikely(page != c->page)) { local_irq_restore(flags); @@ -2887,7 +2907,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, } if (unlikely(!slub_percpu_partial(c))) { local_irq_restore(flags); - goto new_objects; /* stolen by an IRQ handler */ + /* we were preempted and partial list got empty */ + goto new_objects; } page = c->page = slub_percpu_partial(c); @@ -2903,9 +2924,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, if (freelist) goto check_new_page; - put_cpu_ptr(s->cpu_slab); + slub_put_cpu_ptr(s->cpu_slab); page = new_slab(s, gfpflags, node); - c = get_cpu_ptr(s->cpu_slab); + c = slub_get_cpu_ptr(s->cpu_slab); if (unlikely(!page)) { slab_out_of_memory(s, gfpflags, node); @@ -2988,12 +3009,12 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, * cpu before disabling preemption. Need to reload cpu area * pointer. */ - c = get_cpu_ptr(s->cpu_slab); + c = slub_get_cpu_ptr(s->cpu_slab); #endif p = ___slab_alloc(s, gfpflags, node, addr, c); #ifdef CONFIG_PREEMPT_COUNT - put_cpu_ptr(s->cpu_slab); + slub_put_cpu_ptr(s->cpu_slab); #endif return p; } @@ -3522,7 +3543,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, * IRQs, which protects against PREEMPT and interrupts * handlers invoking normal fastpath. */ - c = get_cpu_ptr(s->cpu_slab); + c = slub_get_cpu_ptr(s->cpu_slab); local_irq_disable(); for (i = 0; i < size; i++) { @@ -3568,7 +3589,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, } c->tid = next_tid(c->tid); local_irq_enable(); - put_cpu_ptr(s->cpu_slab); + slub_put_cpu_ptr(s->cpu_slab); /* * memcg and kmem_cache debug support and memory initialization. @@ -3578,7 +3599,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, slab_want_init_on_alloc(flags, s)); return i; error: - put_cpu_ptr(s->cpu_slab); + slub_put_cpu_ptr(s->cpu_slab); slab_post_alloc_hook(s, objcg, flags, i, p, false); __kmem_cache_free_bulk(s, i, p); return 0;