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=-17.7 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,NICE_REPLY_A,SPF_HELO_NONE,URIBL_BLOCKED, 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 E2B19C48BE8 for ; Mon, 14 Jun 2021 11:19:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CCD3D6115B for ; Mon, 14 Jun 2021 11:19:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235283AbhFNLVr (ORCPT ); Mon, 14 Jun 2021 07:21:47 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:59164 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235185AbhFNLJS (ORCPT ); Mon, 14 Jun 2021 07:09:18 -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-out1.suse.de (Postfix) with ESMTPS id A889421976; Mon, 14 Jun 2021 11:07:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1623668834; 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=d5mfqtWi1SWh7XqBauc489hxPzpEgPr8+VSbUtgr/fc=; b=ubc7v5HUMVBdCmBjizOvGgbVgnb/M4vLsZ2WsBfCilr3ccAvZSiSPRheuXAGHpuEPmMNkt iinUYAOU6ykYA5Q1V/JVrg8ib3A2667EjNQT3FsxKK6ElPosQMtQ//oY3KqNIOGttxq54w EInNP6Tcdgdg4e68n5sQ6gwRCc240nk= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1623668834; 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=d5mfqtWi1SWh7XqBauc489hxPzpEgPr8+VSbUtgr/fc=; b=20JgQTItE5fW94MmKJmExmm6tq2IRQPsEJQJOLaLyrNT0L/PVJYhQtINN5BMfoCYFOHoV0 jg0yuvcr515sPCCQ== Received: from imap3-int (imap-alt.suse-dmz.suse.de [192.168.254.47]) by imap.suse.de (Postfix) with ESMTP id 82C74118DD; Mon, 14 Jun 2021 11:07:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1623668834; 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=d5mfqtWi1SWh7XqBauc489hxPzpEgPr8+VSbUtgr/fc=; b=ubc7v5HUMVBdCmBjizOvGgbVgnb/M4vLsZ2WsBfCilr3ccAvZSiSPRheuXAGHpuEPmMNkt iinUYAOU6ykYA5Q1V/JVrg8ib3A2667EjNQT3FsxKK6ElPosQMtQ//oY3KqNIOGttxq54w EInNP6Tcdgdg4e68n5sQ6gwRCc240nk= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1623668834; 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=d5mfqtWi1SWh7XqBauc489hxPzpEgPr8+VSbUtgr/fc=; b=20JgQTItE5fW94MmKJmExmm6tq2IRQPsEJQJOLaLyrNT0L/PVJYhQtINN5BMfoCYFOHoV0 jg0yuvcr515sPCCQ== Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id bopqH2I4x2ASBgAALh3uQQ (envelope-from ); Mon, 14 Jun 2021 11:07:14 +0000 Subject: Re: [RFC v2 33/34] mm, slub: use migrate_disable() on PREEMPT_RT 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 References: <20210609113903.1421-1-vbabka@suse.cz> <20210609113903.1421-34-vbabka@suse.cz> From: Vlastimil Babka Message-ID: Date: Mon, 14 Jun 2021 13:07:14 +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: <20210609113903.1421-34-vbabka@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 6/9/21 1:39 PM, Vlastimil Babka wrote: > 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 even > though it's ultimately a migrate_disable() there. > > 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 | 41 +++++++++++++++++++++++++++++++---------- > 1 file changed, 31 insertions(+), 10 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 12e966f07f19..caa206213e72 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -115,6 +115,26 @@ > * 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. > + */ > +#ifdef CONFIG_PREEMPT_RT > +#define slub_get_cpu_ptr(var) get_cpu_ptr(var) > +#define slub_put_cpu_ptr(var) put_cpu_ptr(var) After Mel's report and bisect pointing to this patch, I realized I got the #ifdef wrong and it should be #ifnded Fixed patch follows: ----8<---- >From e79e166414b8c22e3bcf73a9383bafe802fa64d2 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 21 May 2021 14:03:23 +0200 Subject: [PATCH] mm, slub: use migrate_disable() on PREEMPT_RT 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 even though it's ultimately a migrate_disable() there. 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 | 41 +++++++++++++++++++++++++++++++---------- 1 file changed, 31 insertions(+), 10 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 12e966f07f19..f0359b0c8154 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -115,6 +115,26 @@ * 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); @@ -2419,7 +2439,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) int pages; int pobjects; - preempt_disable(); + slub_get_cpu_ptr(s->cpu_slab); do { pages = 0; pobjects = 0; @@ -2450,7 +2470,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage); - preempt_enable(); + slub_put_cpu_ptr(s->cpu_slab); #endif /* CONFIG_SLUB_CPU_PARTIAL */ } @@ -2759,7 +2779,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, if (unlikely(!pfmemalloc_match(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); @@ -2818,7 +2838,8 @@ 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); @@ -2834,9 +2855,9 @@ 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); @@ -2919,12 +2940,12 @@ 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_PREEMPTION - put_cpu_ptr(s->cpu_slab); + slub_put_cpu_ptr(s->cpu_slab); #endif return p; } @@ -3445,7 +3466,7 @@ 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++) { @@ -3491,7 +3512,7 @@ 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. -- 2.32.0