From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13DD33064B9 for ; Tue, 30 Sep 2025 15:20:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.130 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759245640; cv=none; b=j75Ynejm4Hpte5plDUBHlwBvz0eEcHfTph8P1E5yeyBITZxlQomOG/GFNqEHk+srnmNetCmSHmAw09SC0kL4ToOxohoIAvbaY01Oka+6w5VBueV1JtqXgJUUi/6evsC3Q/33hUylPnw4Nu2yD9ywPhk572e8QjuTqnrMCYcLJ0k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759245640; c=relaxed/simple; bh=I2SYnV3DK+ZS+dO0yzqZccRYN1BXhg8zpAfFlXEI5CE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Na65jIyqYpbwS0pn2b7GN6Z8nVHrWMwGrsWnBXRVo3bL7mEnZfDPb+rsyUH9O5wGTGHLCUBV0utKB49K0Q/KKagEBcbFOwO5c4S1EOQtp56vbhSJLYLvoMmBhTtnuTQ/2//hlv5lUY/nRBl+2NCHRMRY0R90JxPuEGBn5obJkFQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=wa3ooWwz; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=iMDiVHkC; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=wa3ooWwz; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=iMDiVHkC; arc=none smtp.client-ip=195.135.223.130 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="wa3ooWwz"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="iMDiVHkC"; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="wa3ooWwz"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="iMDiVHkC" 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 4845E33694; Tue, 30 Sep 2025 15:20:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1759245635; 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=gd2qT68HUE4EIRZvibhNEqpEUn00xzNgkHBgMBOCgts=; b=wa3ooWwzTJsztv853h+TJU4PhMezZDPlASPLWLPPWi9hrK9eZzsFf/HezvGFP0lV1VHDUB RA+ZDby28/38iCKSN89M/zqnXs6I5F8MTI7596a6tWLbTLOYhg6cW28dpeArbNbiiDhG92 vdmmQ4OkVjjwGprXuq+9lF/NuBmGhlI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1759245635; 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=gd2qT68HUE4EIRZvibhNEqpEUn00xzNgkHBgMBOCgts=; b=iMDiVHkC3gUrFDletyifwdSwtGl2Rz/jIG3SVSOq9+i1DJY3i0am4wcMDJ79825NWAi4yG 79Jm/LdWVm3eb6Cg== Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=wa3ooWwz; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=iMDiVHkC DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1759245635; 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=gd2qT68HUE4EIRZvibhNEqpEUn00xzNgkHBgMBOCgts=; b=wa3ooWwzTJsztv853h+TJU4PhMezZDPlASPLWLPPWi9hrK9eZzsFf/HezvGFP0lV1VHDUB RA+ZDby28/38iCKSN89M/zqnXs6I5F8MTI7596a6tWLbTLOYhg6cW28dpeArbNbiiDhG92 vdmmQ4OkVjjwGprXuq+9lF/NuBmGhlI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1759245635; 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=gd2qT68HUE4EIRZvibhNEqpEUn00xzNgkHBgMBOCgts=; b=iMDiVHkC3gUrFDletyifwdSwtGl2Rz/jIG3SVSOq9+i1DJY3i0am4wcMDJ79825NWAi4yG 79Jm/LdWVm3eb6Cg== 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 275F21342D; Tue, 30 Sep 2025 15:20:35 +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 u8rBB0P122ijaAAAD6G6ig (envelope-from ); Tue, 30 Sep 2025 15:20:35 +0000 Message-ID: <5181a289-eee7-42c1-8bdb-7b7bb463babc@suse.cz> Date: Tue, 30 Sep 2025 17:20:34 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v0] mm/page_alloc: Cleanup for __del_page_from_free_list() Content-Language: en-US To: Zi Yan , Matthew Wilcox Cc: zhongjinji , akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, liulu.liu@honor.com, feng.han@honor.com References: <20250925085006.23684-1-zhongjinji@honor.com> <6fa0e2e3-045e-446f-8ef3-955711b6aa82@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-Spam-Level: X-Spam-Flag: NO X-Rspamd-Queue-Id: 4845E33694 X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,bootlin.com:url,suse.cz:dkim,suse.cz:mid,suse.cz:email]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+] X-Spam-Score: -4.51 On 9/30/25 16:28, Zi Yan wrote: > On 30 Sep 2025, at 9:55, Vlastimil Babka wrote: > >> On 9/25/25 10:50, zhongjinji wrote: >>> It is unnecessary to set page->private in __del_page_from_free_list(). >>> >>> If the page is about to be allocated, page->private will be cleared by >>> post_alloc_hook() before the page is handed out. If the page is expanded >>> or merged, page->private will be reset by set_buddy_order, and no one >>> will retrieve the page's buddy_order without the PageBuddy flag being set. >>> If the page is isolated, it will also reset page->private when it >>> succeeds. >> >> Seems correct. > > This means high order free pages will have head[2N].private set to a non-zero > value, where head[N*2].private is 1, head[N*(2^2)].private is 2, ... > head[N*(2^M)].private is M and head[0].private is the actual free page order. Hm right, tail pages... > If such a high order free page is used as high order folio, it should be fine. We don't reinterpret the private field in any of the first X tail pages for folios? That would be bad too. > But if user allocates a non-compound high order page and uses split_page() > to get a list of order-0 pages from this high order page, some pages will > have non zero private. I wonder if these users are prepared for that. > > For example, kernel/events/ring_buffer.c does it. In its comment, it says > “set its first page's private to this order; !PagePrivate(page) means it's > just a normal page.” > (see https://elixir.bootlin.com/linux/v6.17/source/kernel/events/ring_buffer.c#L634) > > I wonder if non zero page->private would cause any issue there. > > Maybe split_page() should set all page->private to 0. > > Let me know if I get anything wrong. Maybe we could postpone this optimization until struct pages are shrunk. >> >>> Since __del_page_from_free_list() is a hot path in the kernel, it would be >>> better to remove the unnecessary set_page_private(). >>> >>> Signed-off-by: zhongjinji >> >> Reviewed-by: Vlastimil Babka >> >>> --- >>> mm/page_alloc.c | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index d1d037f97c5f..1999eb7e7c14 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -868,7 +868,6 @@ static inline void __del_page_from_free_list(struct page *page, struct zone *zon >>> >>> list_del(&page->buddy_list); >>> __ClearPageBuddy(page); >>> - set_page_private(page, 0); >>> zone->free_area[order].nr_free--; >>> >>> if (order >= pageblock_order && !is_migrate_isolate(migratetype)) > > > Best Regards, > Yan, Zi