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imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=OUY5ujnZ; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770294510; a=rsa-sha256; cv=none; b=RM44uyWoIewKmv2Y+U6Zd005MRYNcR2WLo81ojZB8rnkH80476rpv/l+nt9sBV4nl/yRlv P6X9qzDOhZQqeVpJwUxJBZAU90KseGS4x4SqZAmtVn53PL6+ICsO2//YiWAAz8cl1/cLlz 4w5VNQiF22QSVkyXE1gD1KwacBTdYBU= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2FC3760122; Thu, 5 Feb 2026 12:28:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 42A15C4CEF7; Thu, 5 Feb 2026 12:28:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770294509; bh=JLjHuaflZfzUh9nlPVIutHCb9gfPWwFA1h4yi6Z5VtA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OUY5ujnZ950mNiCDLhuXt4HvGmvKuaTLlJKxOsUgUo6/iVrpV6jGLVQdwkQuc3ktJ /zcfQl5k8nFERPVdLCn3u4EuBfxkaWeOtkzAqvucf9Ihvay0CkKCZp2lMu0zgElREX XENza4jkXjXdF2YHc7XNJeCtYVtEtaxNPUxDk60reTMZrw0lj+Sbjt02rY4zfVFPHa nJTI8XWBlztd/b/2eiEHKfXdS3pQ3GupqjLvQ1Ld9gLEQvOOznLMBYRNsT1c7JyGou TG/Zoueg0XJx6b0WeVk0V8ioiDfz+uVca8uZB8MLI8EKeYRa6aPIA1QNtn2thmmFCg DmXWqe0kNtF9Q== Message-ID: <93ec17e6-e39a-4575-a592-0a1d6c47b30a@kernel.org> Date: Thu, 5 Feb 2026 13:28:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v6 2/5] mm: khugepaged: refine scan progress number To: Dev Jain , Vernon Yang 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> <4f719bed-89bf-44f3-a1cc-39ddc7c66824@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: xrejcrreqn8sf9y3o4ndfqsmefiku8dh X-Rspamd-Queue-Id: C9B9540006 X-Rspam-User: X-HE-Tag: 1770294510-309407 X-HE-Meta: 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 7Y+UYHMI 4NdKfLERRGs5JlE0ud3ljRM5flNN8xYcXfqL5T5FCv6NrKFmqpbMznVmsbiNXniIurxfk6gw7qql5PwNeSzlqHN5ZmwHnFkHAMhKhfiaC9FYrIehJdGW+M6P2J7D+ZNusQD+vmBes4bkuOOKWJO8VeDcZ56Zi4nBx+BkEXG7wEDTnoz5Pgg/nNYTO5UHB1/Myb62lORNH3I6skhCrd2V7CWxTdSnCWHqlzgQhb4kC2OhvLmuxDpLtL6bZBkcvnn+hRem16nYiNNNk+DVraLTFL5P1dJq6DA1v5q8gc7GE8iHkxZDZF3LLyHKzLWnhWxjhIxycb4PqU0v0/4I6wMp3gtuaWD/WefDsskEDZ3NPzZoTNfk= 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 2/5/26 13:07, Dev Jain wrote: > > On 05/02/26 11:38 am, Vernon Yang wrote: >> On Thu, Feb 5, 2026 at 5:35 AM David Hildenbrand (arm) wrote: >>> [...] >>> >>> *cur_progress = max(_pte - pte + 1, HPAGE_PMD_NR); >> I guess, your meaning is "min(_pte - pte + 1, HPAGE_PMD_NR)", not max(). >> >>> ? >>> >>> It's still a bit nasty, though. >>> >>> Can't we just add one at the beginning of the loop and let the compiler >>> optimize that? ;) >> 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]. >> >> [1] https://lore.kernel.org/linux-mm/7c4b5933-7bbd-4ad7-baef-830304a09485@arm.com >> >> If you have a strong recommendation for this, please let me know, Thanks! > > I haven't explicitly checked with assembly, but I am fairly sure this won't get optimized. > There are two cases where it could have been optimized: > > 1) Had the compiler inlined hpage_collapse_scan_pmd Yeah, there are two callers so that likely does not happen. > 2) Had the compiler done something like > if (p) -> foo(), where foo() contains the complete for loop, with the increment > else -> bar(), where bar() contains the complete for loop, without the increment > > Both of which are highly unlikely because of the complexity of the function. Not sure if the compiler would be to optimize this out also in non-inlined cases. In any case, I wonder if this must be optimized at all ... -- Cheers, David