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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 887F2C61D9B for ; Wed, 22 Nov 2023 11:54:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343928AbjKVLyh (ORCPT ); Wed, 22 Nov 2023 06:54:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343577AbjKVLyf (ORCPT ); Wed, 22 Nov 2023 06:54:35 -0500 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A600A91 for ; Wed, 22 Nov 2023 03:54:31 -0800 (PST) Message-ID: <2af8c92f-0de8-4528-af43-6c6e8c1ebdf3@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1700654069; h=from:from:reply-to:subject:subject: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=w6S6GhgWCLr2fBePToOFsmLbaAYhQrMNvt6c0ZCFP3E=; b=CkvBBoVtbQFXbcn51xq+SvlnJyPpMrvavl7P/GHmAoKWuxpv6JCugIRNHZSPGQlx+qNsOm YTf3i83/b2jqKClSJ2+YQM2eggupoYLKNpX/+NQV3tShmTCfcSr98VJDggnAozrDp1Jve5 KvsaDOXt76xMwYfQGCZsUPr91fJzg8A= Date: Wed, 22 Nov 2023 19:54:22 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs Content-Language: en-US To: Vlastimil Babka , Mark Brown Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chengming Zhou , Matthew Wilcox References: <20231102032330.1036151-1-chengming.zhou@linux.dev> <20231102032330.1036151-7-chengming.zhou@linux.dev> <4f3bc1bd-ea87-465d-b58a-0ed57b15187b@sirena.org.uk> <83ff4b9e-94f1-8b35-1233-3dd414ea4dfe@suse.cz> <4ebc67be-8286-17e9-da33-225ed75509a6@suse.cz> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: <4ebc67be-8286-17e9-da33-225ed75509a6@suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/11/22 19:40, Vlastimil Babka wrote: > On 11/22/23 12:35, Chengming Zhou wrote: >> On 2023/11/22 17:37, Vlastimil Babka wrote: >>> On 11/20/23 19:49, Mark Brown wrote: >>>> On Thu, Nov 02, 2023 at 03:23:27AM +0000, chengming.zhou@linux.dev wrote: >>>>> From: Chengming Zhou >>>>> >>>>> Now we will freeze slabs when moving them out of node partial list to >>>>> cpu partial list, this method needs two cmpxchg_double operations: >>>>> >>>>> 1. freeze slab (acquire_slab()) under the node list_lock >>>>> 2. get_freelist() when pick used in ___slab_alloc() >>>> >>>> Recently -next has been failing to boot on a Raspberry Pi 3 with an arm >>>> multi_v7_defconfig and a NFS rootfs, a bisect appears to point to this >>>> patch (in -next as c8d312e039030edab25836a326bcaeb2a3d4db14) as having >>>> introduced the issue. I've included the full bisect log below. >>>> >>>> When we see problems we see RCU stalls while logging in, for example: >>> >>> Can you try this, please? >>> >> >> Great! I manually disabled __CMPXCHG_DOUBLE to reproduce the problem, >> and this patch can solve the machine hang problem. >> >> BTW, I also did the performance testcase on the machine with 128 CPUs. >> >> stress-ng --rawpkt 128 --rawpkt-ops 100000000 >> >> base patched >> 2.22s 2.35s >> 2.21s 3.14s >> 2.19s 4.75s >> >> Found this atomic version performance numbers are not stable. > > That's weirdly too bad. Is that measured also with __CMPXCHG_DOUBLE > disabled, or just the patch? The PG_workingset flag change should be The performance test is just the patch. > uncontended as we are doing it under list_lock, and with __CMPXCHG_DOUBLE > there should be no interfering PG_locked interference. > Yes, I don't know. Maybe it's related with my kernel config, making the atomic operation much expensive? Will look again.. And I also tested the atomic-optional version like below, found the performance numbers are much stable. diff --git a/mm/slub.c b/mm/slub.c index a307d319e82c..e11d34d51a14 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -531,7 +531,7 @@ static __always_inline void slab_unlock(struct slab *slab) struct page *page = slab_page(slab); VM_BUG_ON_PAGE(PageTail(page), page); - __bit_spin_unlock(PG_locked, &page->flags); + bit_spin_unlock(PG_locked, &page->flags); } static inline bool @@ -2136,12 +2136,18 @@ static inline bool slab_test_node_partial(const struct slab *slab) static inline void slab_set_node_partial(struct slab *slab) { - __set_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); + if (slab->slab_cache->flags & __CMPXCHG_DOUBLE) + __set_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); + else + set_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); } static inline void slab_clear_node_partial(struct slab *slab) { - __clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); + if (slab->slab_cache->flags & __CMPXCHG_DOUBLE) + __clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); + else + clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0)); }