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Fri, 06 Feb 2026 03:12:58 -0800 (PST) Date: Fri, 6 Feb 2026 19:12:46 +0800 From: Vernon Yang To: "David Hildenbrand (Arm)" Cc: Dev Jain , 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 Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number Message-ID: <6zltgzs24wpypzu36ldwgtzilhv2z3ofuu45azp5u45huiwqvj@6jhhp5r24po6> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1a6d8295-e27b-4440-a367-af0432a7af4f@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D34FE180010 X-Stat-Signature: km9bzyzqsyyeun5wg7zmf5saud3ngq8m X-HE-Tag: 1770376379-14558 X-HE-Meta: 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 0Ps9AxDg 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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 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". -- Thanks, Vernon