From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15086C48BCD for ; Wed, 9 Jun 2021 11:40:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0669B613B6 for ; Wed, 9 Jun 2021 11:40:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239268AbhFILmR (ORCPT ); Wed, 9 Jun 2021 07:42:17 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:46972 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239148AbhFILl3 (ORCPT ); Wed, 9 Jun 2021 07:41:29 -0400 Received: from imap.suse.de (imap-alt.suse-dmz.suse.de [192.168.254.47]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id B0C2F1FD65; Wed, 9 Jun 2021 11:39:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1623238773; 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=SlrL7OICvBFstNZZ2XJMriwG3NzNdu907jHbbChxuc0=; b=CjpVp1rLvDZ8dbeBqHACPad2h/djS+XV2r2Cj3do2Z8zJCcvNb2LUc7OaGw7nz8jSBMrce hPm05vums1nTQYrZuX3cyHPuk6MrLNu6uD7Yi8AgBjy1UvKVT2U6fSCoU70yTi2wbXXnJ1 LQn1zYDMtQEE95DVYNivcrhGabQyBkU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1623238773; 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=SlrL7OICvBFstNZZ2XJMriwG3NzNdu907jHbbChxuc0=; b=chweC4mL0L1KS071i9+/f0T+CnbFaP0Q3h2vvFwS8OMkyyyELVt2u99fphybzOc8OHFKfP if05UsHtBxkDzjBQ== Received: from imap3-int (imap-alt.suse-dmz.suse.de [192.168.254.47]) by imap.suse.de (Postfix) with ESMTP id 8155C11A98; Wed, 9 Jun 2021 11:39:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1623238773; 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=SlrL7OICvBFstNZZ2XJMriwG3NzNdu907jHbbChxuc0=; b=CjpVp1rLvDZ8dbeBqHACPad2h/djS+XV2r2Cj3do2Z8zJCcvNb2LUc7OaGw7nz8jSBMrce hPm05vums1nTQYrZuX3cyHPuk6MrLNu6uD7Yi8AgBjy1UvKVT2U6fSCoU70yTi2wbXXnJ1 LQn1zYDMtQEE95DVYNivcrhGabQyBkU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1623238773; 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=SlrL7OICvBFstNZZ2XJMriwG3NzNdu907jHbbChxuc0=; b=chweC4mL0L1KS071i9+/f0T+CnbFaP0Q3h2vvFwS8OMkyyyELVt2u99fphybzOc8OHFKfP if05UsHtBxkDzjBQ== Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id OLEaH3WowGD6XgAALh3uQQ (envelope-from ); Wed, 09 Jun 2021 11:39:33 +0000 From: Vlastimil Babka To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim Cc: Sebastian Andrzej Siewior , Thomas Gleixner , Mel Gorman , Jesper Dangaard Brouer , Peter Zijlstra , Jann Horn , Vlastimil Babka Subject: [RFC v2 11/34] mm, slub: simplify kmem_cache_cpu and tid setup Date: Wed, 9 Jun 2021 13:38:40 +0200 Message-Id: <20210609113903.1421-12-vbabka@suse.cz> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210609113903.1421-1-vbabka@suse.cz> References: <20210609113903.1421-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In slab_alloc_node() and do_slab_free() fastpaths we need to guarantee that our kmem_cache_cpu pointer is from the same cpu as the tid value. Currently that's done by reading the tid first using this_cpu_read(), then the kmem_cache_cpu pointer and verifying we read the same tid using the pointer and plain READ_ONCE(). This can be simplified to just fetching kmem_cache_cpu pointer and then reading tid using the pointer. That guarantees they are from the same cpu. We don't need to read the tid using this_cpu_read() because the value will be validated by this_cpu_cmpxchg_double(), making sure we are on the correct cpu and the freelist didn't change by anyone preempting us since reading the tid. Signed-off-by: Vlastimil Babka Acked-by: Mel Gorman --- mm/slub.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 0d5c253a39b2..6d6a9a69db8a 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2822,15 +2822,14 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, * reading from one cpu area. That does not matter as long * as we end up on the original cpu again when doing the cmpxchg. * - * We should guarantee that tid and kmem_cache are retrieved on - * the same cpu. It could be different if CONFIG_PREEMPTION so we need - * to check if it is matched or not. + * We must guarantee that tid and kmem_cache_cpu are retrieved on the + * same cpu. We read first the kmem_cache_cpu pointer and use it to read + * the tid. If we are preempted and switched to another cpu between the + * two reads, it's OK as the two are still associated with the same cpu + * and cmpxchg later will validate the cpu. */ - do { - tid = this_cpu_read(s->cpu_slab->tid); - c = raw_cpu_ptr(s->cpu_slab); - } while (IS_ENABLED(CONFIG_PREEMPTION) && - unlikely(tid != READ_ONCE(c->tid))); + c = raw_cpu_ptr(s->cpu_slab); + tid = READ_ONCE(c->tid); /* * Irqless object alloc/free algorithm used here depends on sequence @@ -3104,11 +3103,8 @@ static __always_inline void do_slab_free(struct kmem_cache *s, * data is retrieved via this pointer. If we are on the same cpu * during the cmpxchg then the free will succeed. */ - do { - tid = this_cpu_read(s->cpu_slab->tid); - c = raw_cpu_ptr(s->cpu_slab); - } while (IS_ENABLED(CONFIG_PREEMPTION) && - unlikely(tid != READ_ONCE(c->tid))); + c = raw_cpu_ptr(s->cpu_slab); + tid = READ_ONCE(c->tid); /* Same with comment on barrier() in slab_alloc_node() */ barrier(); -- 2.31.1