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 3FA96EF06E2 for ; Sun, 8 Feb 2026 09:05:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 106EB6B0089; Sun, 8 Feb 2026 04:05:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0B5366B0092; Sun, 8 Feb 2026 04:05:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F02F66B0093; Sun, 8 Feb 2026 04:05:20 -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 DCBDD6B0089 for ; Sun, 8 Feb 2026 04:05:20 -0500 (EST) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 7B0BED5F7C for ; Sun, 8 Feb 2026 09:05:20 +0000 (UTC) X-FDA: 84420705600.18.371F373 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf14.hostedemail.com (Postfix) with ESMTP id 95066100003 for ; Sun, 8 Feb 2026 09:05:18 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf14.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770541519; 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; bh=QJA6wXQCKXrTREPUSprJrSBZffzBC4OBjqTIpe7vjlQ=; b=DmCWb0sNOhmg0+uSIO2HK//mkCO+kSBijGKdm9Z+tRfE8Hw94vf2yb6hH2OSpntUzk5W26 jIqrWfmFl57dgcuztxzDQBNmgbvmxyx3Eruob9e1a8UMRH+2c0xUwACQICe0JPJEWBv8G1 kQ1PjXetj5gFiYsjWAmadxlwJEvnebs= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770541519; a=rsa-sha256; cv=none; b=aWMO6X1L83Wd3rhJzfiDSweWh0OTbkvDWg6CRtJdhSifpgmjY7TIS56YYi+DbF7LKQVMWh eyv/V195Kg568SSiZD01GsTADcAu1jUuZnqj4CgkRPwcE4gzmKWTXK2j3uUAaODS/aIOKH YRZYFXNPX0fye8OLrXC6XsTKvuDnj1E= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf14.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2A319339; Sun, 8 Feb 2026 01:05:11 -0800 (PST) Received: from [10.164.10.250] (unknown [10.164.10.250]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 862A53F740; Sun, 8 Feb 2026 01:05:14 -0800 (PST) Message-ID: <78b9bb1c-21aa-435f-a697-ebbfbe604a5a@arm.com> Date: Sun, 8 Feb 2026 14:35:11 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number To: Vernon Yang , "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baohua@kernel.org, lance.yang@linux.dev, 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> Content-Language: en-US From: Dev Jain In-Reply-To: <6zltgzs24wpypzu36ldwgtzilhv2z3ofuu45azp5u45huiwqvj@6jhhp5r24po6> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 95066100003 X-Stat-Signature: o9ci41m8ys7khho8b58141tfqihdxati X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770541518-361481 X-HE-Meta: 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 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 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. > -- > Thanks, > Vernon