From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 15DEE3ED11F for ; Fri, 6 Feb 2026 13:52:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770385973; cv=none; b=Mxr46K+avzwiJv7LUjDVA0uJh7wH/SoZDYvA+SwKs9/jvgG1Lw+xrmHCtyOOzDMj1PygNv6Jqh7mPyV3rfh+Okf7wPBBhaYx4ecaxWL3+Z2nzFfHYJNg8LvVA+CulEHGHoEGcbm+Q29ExjrwI2SPZO2GdDJoU+fWUeJ/hLlfs0M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770385973; c=relaxed/simple; bh=q/0eEYelPoHp9GziLKUj6jB6Qb4P/c1vA9n+PCbyfC0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qz19YGaIuojN2Ent3wxZMxIcYrwMGaLO2m22Z8tA93Rlwl8PtagHu/xyhA8IJlsrfewXba+NtbqInzV/pl/qLi5se40FjoYmZ9cP3H7nbFwub9YlXGWuVHehYiXnpTW+K6/ngL4js7U8txsqpMsk3ZctozcwVjiN2DUh9qVUzsU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lVArVqdL; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lVArVqdL" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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