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=-13.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 89226C4320A for ; Sun, 25 Jul 2021 19:13:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59D0760249 for ; Sun, 25 Jul 2021 19:13:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231405AbhGYScz (ORCPT ); Sun, 25 Jul 2021 14:32:55 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:57058 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231215AbhGYScx (ORCPT ); Sun, 25 Jul 2021 14:32:53 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 smtp-out1.suse.de (Postfix) with ESMTPS id 4963521EF9; Sun, 25 Jul 2021 19:13:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1627240402; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=oCzLE+ap2mKmrXNTbUV0BiILf9trfJCBHHM1JEd+uDE=; b=vexRAjv4d7CgGQqib19vcceFhpEmaNw0VpYkuu3TUVvt5X5uk66XSGQboG3r6C6xMF3PKc 9y32lkpGOBb87MNLGa85OxtoawGenBUhp0Kw4qN/WfI+/igvJNg7ghUpe7Lo7et2YqYuyQ RAPlEwBwwlqnWS4pnGcN4kj+yMpnkYE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1627240402; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=oCzLE+ap2mKmrXNTbUV0BiILf9trfJCBHHM1JEd+uDE=; b=W9++s5wXbcaazYIEp16a5PjUjX8i7jesnXsQq1zn6+0WyiU7kAprOYDlY4QYtVHhM35bPm ob8jGWz25o7P6aBA== Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 imap1.suse-dmz.suse.de (Postfix) with ESMTPS id 1CE4213277; Sun, 25 Jul 2021 19:13:22 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id yFPGBdK3/WBqNgAAGKfGzw (envelope-from ); Sun, 25 Jul 2021 19:13:22 +0000 Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope From: Vlastimil Babka To: Mike Galbraith , Thomas Gleixner , LKML Cc: linux-rt-users@vger.kernel.org, Mel Gorman , Sebastian Andrzej Siewior References: <87tul5p2fa.ffs@nanos.tec.linutronix.de> <8c0e0c486056b5185b58998f2cce62619ed3f05c.camel@gmx.de> <878s2fnv79.ffs@nanos.tec.linutronix.de> <6c0e20dd84084036d5068e445746c3ed7e82ec4b.camel@gmx.de> <7431ceb9761c566cf2d1f6f263247acd8d38c4b5.camel@gmx.de> <240f104fc6757d8c38fa01342511eda931632d5a.camel@gmx.de> <69da2ecd-a797-e264-fbfa-13108dc7a573@suse.cz> <84a7bd02cf109c6a5a8c7cc2bfc2898cb98270aa.camel@gmx.de> <5be1a703-9a0a-4115-1d69-634e5e8ecefd@suse.cz> <76dedfc3-0497-1776-d006-486b9bfd88da@suse.cz> <72a045663bf8f091ae11dd328d5e085541d54fcd.camel@gmx.de> <18ca0ce9-3407-61e1-31d6-5c48e80eb5bb@suse.cz> Message-ID: <73f032c2-70f1-77b6-9fd2-9aca52fd5b4d@suse.cz> Date: Sun, 25 Jul 2021 21:12:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <18ca0ce9-3407-61e1-31d6-5c48e80eb5bb@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/25/21 6:27 PM, Vlastimil Babka wrote: >>> Hope fixing that helps then? >> >> Yeah, though RT should perhaps be pinned across release/re-acquire? > > Probably not necessary, this_cpu_cmpxchg() will effectively recognize > being moved to a different CPU. > Might also move __unfreeze_partials() out of the whole loop to avoid the > relock. Yeah that should be better. > >> Actually, local locks should rediscover the recursion handling skills >> they long had so such RT specific hole poking isn't necessary. There >> previously would have been no ifdef+typo there for eyeballs to miss and >> miss and miss. > > Hm, now I'm realizing that local_lock() on !RT is just > preempt_disable(), i.e. equivalent to get_cpu_ptr(), so some of the > ifdeffery could go away? How much will this explode? Thanks. ----8<---- >From 99808b198bdf867951131bb9d1ca1bd1cd12b8c4 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 23 Jul 2021 23:17:18 +0200 Subject: [PATCH] PREEMPT_RT+SLUB_CPU_PARTIAL fix attempt --- mm/slub.c | 34 +++++++++++++++++++++++++++++++--- 1 file changed, 31 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 581004a5aca9..d12a50b5ee6f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2437,13 +2437,19 @@ static void unfreeze_partials(struct kmem_cache *s) { struct page *partial_page; +#ifndef CONFIG_PREEMPT_RT do { partial_page = this_cpu_read(s->cpu_slab->partial); } while (partial_page && this_cpu_cmpxchg(s->cpu_slab->partial, partial_page, NULL) != partial_page); - +#else + local_lock(&s->cpu_slab->lock); + partial_page = this_cpu_read(s->cpu_slab->partial); + this_cpu_write(s->cpu_slab->partial, NULL); + local_unlock(&s->cpu_slab->lock); +#endif if (partial_page) __unfreeze_partials(s, partial_page); } @@ -2479,10 +2485,15 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) { #ifdef CONFIG_SLUB_CPU_PARTIAL struct page *oldpage; + struct page *page_to_unfreeze = NULL; int pages; int pobjects; - slub_get_cpu_ptr(s->cpu_slab); + /* + * On !RT we just want to disable preemption, on RT we need the lock + * for real. This happens to match local_lock() semantics. + */ + local_lock(&s->cpu_slab->lock); do { pages = 0; pobjects = 0; @@ -2496,7 +2507,16 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) * partial array is full. Move the existing * set to the per node partial list. */ +#ifndef CONFIG_PREEMPT_RT unfreeze_partials(s); +#else + /* + * Postpone unfreezing until we drop the local + * lock to avoid relocking. + */ + page_to_unfreeze = oldpage; +#endif + oldpage = NULL; pobjects = 0; pages = 0; @@ -2511,9 +2531,17 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) page->pobjects = pobjects; page->next = oldpage; +#ifndef CONFIG_PREEMPT_RT } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage); - slub_put_cpu_ptr(s->cpu_slab); +#else + this_cpu_write(s->cpu_slab->partial, page); + } while (false); +#endif + + local_unlock(&s->cpu_slab->lock); + if (page_to_unfreeze) + __unfreeze_partials(s, page_to_unfreeze); #endif /* CONFIG_SLUB_CPU_PARTIAL */ } -- 2.32.0