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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 50E9DCCF9EB for ; Wed, 29 Oct 2025 22:44:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AA4D28E0113; Wed, 29 Oct 2025 18:44:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A7C6D8E0106; Wed, 29 Oct 2025 18:44:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 96BC98E0113; Wed, 29 Oct 2025 18:44:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 84B148E0106 for ; Wed, 29 Oct 2025 18:44:38 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4C290140942 for ; Wed, 29 Oct 2025 22:44:38 +0000 (UTC) X-FDA: 84052632636.24.7FD921A Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by imf28.hostedemail.com (Postfix) with ESMTP id D1BFEC0006 for ; Wed, 29 Oct 2025 22:44:35 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=KuE6dmbh; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rrpE4k7p; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=KuE6dmbh; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rrpE4k7p; spf=pass (imf28.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.130 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1761777876; h=from:from:sender: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:dkim-signature; bh=nGeK7bx3Hm62BR80qyLU/cEzRG1dQ+GIaNgmFFG3WZk=; b=LmC8F64yHDrGn3CrX4vPBA1CIVf8O16gEy6j0ZyKgA5yuRFI4XjiuX0tvwYU/8pveUNMMo jbXBqp/WyjMr/GOYpyS4eFTaX3dOrTXwLaDeqlmhLaS+mKwsJHYpkQYffzdyiv7jVLjePk 1p5tfov3hTBWbxEwSVuUGXAXd28rj7I= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761777876; a=rsa-sha256; cv=none; b=Ritddx56EeI9iXq5CFUkXiJ3wOyvFa5gVWnENUwcp7V+YfkKTV5nzPdroqZrZk92B8AREg dLqYS2BhkksQiFopQv4IUljSj8T/ypPhen2dGFTRh8qIeTbL98Qp0MXUxsVPK5R+X0Ecpz z037r7HtW/GDj1WuxX2d9CjOYRRNObw= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=KuE6dmbh; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rrpE4k7p; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=KuE6dmbh; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=rrpE4k7p; spf=pass (imf28.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.130 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id F1EC322809; Wed, 29 Oct 2025 22:44:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1761777874; 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:autocrypt:autocrypt; bh=nGeK7bx3Hm62BR80qyLU/cEzRG1dQ+GIaNgmFFG3WZk=; b=KuE6dmbhj3b4/ZjtupyKEiIeT4ZjL+cZZgw2VyuQrj+ANCIYosjf7UNZe+PTbnLl6NVuTs /5E3V0pItQqNqQDwpwRfZ4shHI0yGaKaKsH0M+TjWp/XOc1/PsIwa6d22FdhSu3LNGkZCZ rCPGXFKmwtdJto6uv6bqUqGsLzdF6kw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1761777874; 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:autocrypt:autocrypt; bh=nGeK7bx3Hm62BR80qyLU/cEzRG1dQ+GIaNgmFFG3WZk=; b=rrpE4k7pcP11GeKmOrNuaHpgSCvtvT1MmCr56Q/kxNqL8uSFkgzBdPOWdCpSjUvhCTZWHL YMzANhVFXuX0dlAg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1761777874; 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:autocrypt:autocrypt; bh=nGeK7bx3Hm62BR80qyLU/cEzRG1dQ+GIaNgmFFG3WZk=; b=KuE6dmbhj3b4/ZjtupyKEiIeT4ZjL+cZZgw2VyuQrj+ANCIYosjf7UNZe+PTbnLl6NVuTs /5E3V0pItQqNqQDwpwRfZ4shHI0yGaKaKsH0M+TjWp/XOc1/PsIwa6d22FdhSu3LNGkZCZ rCPGXFKmwtdJto6uv6bqUqGsLzdF6kw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1761777874; 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:autocrypt:autocrypt; bh=nGeK7bx3Hm62BR80qyLU/cEzRG1dQ+GIaNgmFFG3WZk=; b=rrpE4k7pcP11GeKmOrNuaHpgSCvtvT1MmCr56Q/kxNqL8uSFkgzBdPOWdCpSjUvhCTZWHL YMzANhVFXuX0dlAg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id D52821396A; Wed, 29 Oct 2025 22:44:33 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 6jm4M9GYAmlwFAAAD6G6ig (envelope-from ); Wed, 29 Oct 2025 22:44:33 +0000 Message-ID: Date: Wed, 29 Oct 2025 23:44:33 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 12/19] slab: remove the do_slab_free() fastpath Content-Language: en-US To: Alexei Starovoitov Cc: Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm , LKML , linux-rt-devel@lists.linux.dev, bpf , kasan-dev References: <20251023-sheaves-for-all-v1-0-6ffa2c9941c0@suse.cz> <20251023-sheaves-for-all-v1-12-6ffa2c9941c0@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Server: rspam05 X-Stat-Signature: fmoppadgp4puatsittr9dqsnpyeu8r8o X-Rspam-User: X-Rspamd-Queue-Id: D1BFEC0006 X-HE-Tag: 1761777875-499508 X-HE-Meta: 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 LjjZ1SW8 hiPUulJwx2J4kBBKP0hRkKbHIsk4F4eVQn7ST2rq9KeVHk25nqQ/ZsPpBzTDR63KOCZTpwwe5x+Dj18Zz6ZSBKw3wQG1b22qMvXIdqfFL0UZtomC6tjoovchivhqj/DXLnr1uDyn9WKA1M10wB3BIf+XfQx5+IM0wcV0JProy6Nil8oFzSHCzOr7xgr8z/rKvvsgosd9PlNXxoYWK7Wvu/hCS8imyCDpGmFsqPORbTTU/dxqikO0KVAhTPYMSCnsdS/QUEkZO6Vf/yTcZ4nOPYPs8xuRc4sok/rzxV0VpGNO+Lw144xWU0JgPj4TZ8CT/w5Clzj9wzV4HwLS51VbtByAwb+6WWISPmJftslnh+854TAIthecUV6XEu2UJylfOhXhqxz8iTSQLFpTmmp2YXIv7kdZsUQJJlk7H0MnfLW7cpNU= 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: List-Subscribe: List-Unsubscribe: On 10/25/25 00:32, Alexei Starovoitov wrote: > On Thu, Oct 23, 2025 at 6:53 AM Vlastimil Babka wrote: >> @@ -6444,8 +6316,13 @@ void kfree_nolock(const void *object) >> * since kasan quarantine takes locks and not supported from NMI. >> */ >> kasan_slab_free(s, x, false, false, /* skip quarantine */true); >> + /* >> + * __slab_free() can locklessly cmpxchg16 into a slab, but then it might >> + * need to take spin_lock for further processing. >> + * Avoid the complexity and simply add to a deferred list. >> + */ >> if (!free_to_pcs(s, x, false)) >> - do_slab_free(s, slab, x, x, 0, _RET_IP_); >> + defer_free(s, x); > > That should be rare, right? > free_to_pcs() should have good chances to succeed, > and pcs->spare should be there for kmalloc sheaves? Yes. > So trylock failure due to contention in barn_get_empty_sheaf() > and in barn_replace_full_sheaf() should be rare. Yeah, while of course stress tests like will-it-scale can expose nasty corner cases. > But needs to be benchmarked, of course. > The current fast path cmpxchg16 in !RT is very reliable > in my tests. Hopefully this doesn't regress. You mean the one that doesn't go the "if (unlikely(slab != c->slab))" way? Well that unlikely() there might be quite misleading. It will be true when free follows shortly after alloc. If not, c->slab can be exhausted and replaced with a new one. Or the process is migrated to another cpu before freeing. The probability of slab == c->slab staying true drops quickly. So if your tests were doing frees shortly after alloc, you would be indeed hitting it reliably, but is it representative? However sheaves should work reliably as well too with such a pattern, so if some real code really does that significantly, it will not regress.