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 30BC2EF06E3 for ; Sun, 8 Feb 2026 09:32:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 545496B0089; Sun, 8 Feb 2026 04:32:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4F2896B0092; Sun, 8 Feb 2026 04:32:35 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4043D6B0093; Sun, 8 Feb 2026 04:32:35 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 3013C6B0089 for ; Sun, 8 Feb 2026 04:32:35 -0500 (EST) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id D1D6FB9CA7 for ; Sun, 8 Feb 2026 09:32:34 +0000 (UTC) X-FDA: 84420774228.04.0FFEC10 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) by imf28.hostedemail.com (Postfix) with ESMTP id D0D2DC000F for ; Sun, 8 Feb 2026 09:32:32 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=QzmQj6Kn; spf=pass (imf28.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.174 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770543153; 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=TmASjvYRr/8iOkWpBFHMDIcEFajTddtRmV+cC/u8J+0=; b=H3t3ryYTgFNKlOi/hn0n1yUJXid3ci+mb688MdgWF076A3m68dTplF20yEglt8v7gkc41n 4P8lqMGSg5G/MeWCrN8OjVEQhvxY4UW+Dbi/raT+RcqYLOMWj5t+AEM+0oPN7GidHZYTYd eBL27Twgmux2jTlq/TzD7rUG5yOKGUU= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=QzmQj6Kn; spf=pass (imf28.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.174 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770543153; a=rsa-sha256; cv=none; b=2ypsy8UD93d1vSmnMJIOw1HJMBPm/Xi5G9OlpRm0THaeTDWv8rGSfgjsRui1b9ukTzioH8 ykOynSWDZ0nu8IK96ypLOsck8hmms+HkB7LaoOOMdwqL3sNbwH6D+cltG8SU/x95K1UlMO wUzRdgZM00YStyAlpbUtB2rnk2aZ43E= Message-ID: <9942f80a-5a99-4e43-8053-8e6707c39252@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770543150; 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=TmASjvYRr/8iOkWpBFHMDIcEFajTddtRmV+cC/u8J+0=; b=QzmQj6KnX3F1OfGkKBEXhavzhDn0k9imbTb9pT7ynRewH4PpjHDeHWtodwzJgMvPHxCnXo 2IWxeXF1lTnInzvtBSwtl5H2v5K7Fduu/DK7RbUkYgFR2xbpaRHCcm3Tqsk38aK0CEu+qL 5V919FzBg0utsAxp+M424qUGfw+4zAU= Date: Sun, 8 Feb 2026 17:32:23 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number Content-Language: en-US To: Dev Jain , Vernon Yang , "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260201122554.1470071-1-vernon2gm@gmail.com> <20260201122554.1470071-3-vernon2gm@gmail.com> <85e8ded9-a9eb-4663-9c96-93af60006fb6@kernel.org> <9508744b-e5d5-49ef-825f-eef683892541@arm.com> <1a6d8295-e27b-4440-a367-af0432a7af4f@kernel.org> <6zltgzs24wpypzu36ldwgtzilhv2z3ofuu45azp5u45huiwqvj@6jhhp5r24po6> <78b9bb1c-21aa-435f-a697-ebbfbe604a5a@arm.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <78b9bb1c-21aa-435f-a697-ebbfbe604a5a@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D0D2DC000F X-Stat-Signature: 1j8b6ny5u7stfh6xrtqpya6ew4ix6wa5 X-Rspam-User: X-HE-Tag: 1770543152-853504 X-HE-Meta: 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 omf3p79f NO9YM4RovjzS673nH23sG8PHQkE+OIDOcVerbf/078z5Psk+xJQw4jBrRsh0KiQNEWw3ekSciKQ/jUSQk8sMMejuIUw93d/SPLFPtlX/4BvPZ6fqeBUd9KGyZhxh2ODvrwZK44OVFHvdYRwNdzwM+z++jPjisEU4A+rgfFW07Xx0E8G4Jo0IY8txEbnUVOoXPJKZ9mHHEmQnvty3wcK/VJH9lREeK3kne5Foh2RUKM5/pLuzi2f1GlpxeoZxH5UNRN0+P 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 2026/2/8 17:05, Dev Jain wrote: > > On 06/02/26 4:42 pm, Vernon Yang wrote: >> On Fri, Feb 06, 2026 at 10:02:48AM +0100, David Hildenbrand (Arm) wrote: >>> On 2/5/26 15:25, Dev Jain wrote: >>>> On 05/02/26 5:41 pm, David Hildenbrand (arm) wrote: >>>>> On 2/5/26 07:08, Vernon Yang wrote: >>>>>> On Thu, Feb 5, 2026 at 5:35 AM David Hildenbrand (arm) >>>>>> wrote: >>>>>> >>>>>> I guess, your meaning is "min(_pte - pte + 1, HPAGE_PMD_NR)", not max(). >>>>> Yes! >>>>> >>>>>> >>>>>> I'm also worried that the compiler can't optimize this since the body of >>>>>> the loop is complex, as with Dev's opinion [1]. >>>>> Why do we even have to optimize this? :) >>>>> >>>>> Premature ... ? :) >>>> >>>> I mean .... we don't, but the alternate is a one liner using max(). >>> I'm fine with the max(), but it still seems like adding complexity to >>> optimize something that is nowhere prove to really be a problem. >> Hi David, Dev, >> >> I use "*cur_progress += 1" at the beginning of the loop, the compiler >> optimize that. Assembly as follows: >> >> 60c1: 4d 29 ca sub %r9,%r10 // r10 is _pte, r9 is pte, r10 = _pte - pte >> 60c4: b8 00 02 00 00 mov $0x200,%eax // eax = HPAGE_PMD_NR >> 60c9: 44 89 5c 24 10 mov %r11d,0x10(%rsp) // >> 60ce: 49 c1 fa 03 sar $0x3,%r10 // >> 60d2: 49 83 c2 01 add $0x1,%r10 // r10 += 1 >> 60d6: 49 39 c2 cmp %rax,%r10 // r10 = min(r10, eax) >> 60d9: 4c 0f 4f d0 cmovg %rax,%r10 // >> 60dd: 44 89 55 00 mov %r10d,0x0(%rbp) // *cur_progress = r10 >> >> To make the code simpler, Let us use "*cur_progress += 1". > > Wow! Wasn't expecting that. What's your gcc version? I checked with > gcc 11.4.0 (looks pretty old) with both x86 and arm64, and it couldn't > optimize. FWIW, 11.4.0 is newer that the minimum GCC version (8.1) required by kernel. See Documentation/process/changes.rst The optimization might just be version-dependent :)