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 02EACEE20A0 for ; Fri, 6 Feb 2026 13:52:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 30E406B0089; Fri, 6 Feb 2026 08:52:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 29B506B0092; Fri, 6 Feb 2026 08:52:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1C5136B0093; Fri, 6 Feb 2026 08:52:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 09F1F6B0089 for ; Fri, 6 Feb 2026 08:52:56 -0500 (EST) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7EA741401BD for ; Fri, 6 Feb 2026 13:52:55 +0000 (UTC) X-FDA: 84414172710.10.E9D29DE Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) by imf24.hostedemail.com (Postfix) with ESMTP id 5937C18000C for ; Fri, 6 Feb 2026 13:52:53 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=lVArVqdL; spf=pass (imf24.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.177 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=1770385973; 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=JP3JgFFPAC9maJD5a6nNDzrMrZ2Ma5PybmorCwXVQQc=; b=an8Q7/f//gnUykIbrdC13L/u0MXH5r2yo9KC/urbil09oFtCFT1YsB60N0kDimnFIQeEne S9wZukcpXIc3ese6fZ/Z6GTntLkeliM3KT5io+UtG+M6HSp39iKQrPI5hvJ5KsIsQHe1No 8MaXdBL0YgxAHFWUYE5qSlKzVy8V5JI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770385973; a=rsa-sha256; cv=none; b=fF58TtCmFKQ0r1srp3MF4KTYCe5LWtHyq8gNTs9PVzAQEdfp1uJi7N6vjwIFVPSZTm8mwl diLE/N3W/s1SZjSp4qFuOM9eBJzcA47Wc1SkX9xjvi501hwf8Cw+tUyFOea0Yh41Wyq0T0 Bh+8VrzgLfB4X2TnaenGqQu/MSm7CGs= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=lVArVqdL; spf=pass (imf24.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.177 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <2d2eff81-4f7d-41df-8c56-12a050ffb60c@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770385971; 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=JP3JgFFPAC9maJD5a6nNDzrMrZ2Ma5PybmorCwXVQQc=; b=lVArVqdLUbAnuy56x5+9azwBkbzri33c/LkukueMeXy8bzb66WP4nLq/ED69UwITa7+pZh ratVBLPTpvEG+gMCb10g9qRwqOqT4BaRt+3Rw0N4nHfMUAEmlonB3NGHCFWs09qaXIRmlN WQA6so+0GNEqYybG14ycu+vCrPgG1do= Date: Fri, 6 Feb 2026 21:52:28 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number Content-Language: en-US To: Vernon Yang , "David Hildenbrand (Arm)" , Dev Jain 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <6zltgzs24wpypzu36ldwgtzilhv2z3ofuu45azp5u45huiwqvj@6jhhp5r24po6> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 5937C18000C X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 8ayytpshmpuqozfbmj6g5719tfsr4cse X-HE-Tag: 1770385973-533731 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 2026/2/6 19:12, 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". Cool! Compiler did the right thing and the heavy lifting after all - we get to keep it simple :p