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AJvYcCWBO08qHAwNFdGWpMNrGSDkBEjOWNLyxmP/8tswGFVNaS9OeCbW0wnjrKutzzasq60MrarZyd4Ywg==@kvack.org X-Gm-Message-State: AOJu0Yy0072ZZYidtEQ6Pv+7dnpQ2oZwkRN7efACB/GHO4Hig178y+ZT JovKlJ1JA3B/Tbo9w3UK2KMrRVaUVpZXqELX7uqKRI79AJamqx0jF9UCM6v4twzdOCG4Zj4QAlE TdPfINdIyyvLnTg== X-Google-Smtp-Source: AGHT+IECtIVfoHR4KIma4m4xNaSR56A1fkqF050K07bUAlHAQawhC7HGe3mmGgV7rlzdWxH4OyA8KDgAIxJQhA== X-Received: from wmpl35.prod.google.com ([2002:a05:600c:8a3:b0:475:d8de:fe5b]) (user=jackmanb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:4744:b0:46e:48fd:a1a9 with SMTP id 5b1f17b1804b1-4778fea8ab2mr28900845e9.33.1763123769520; Fri, 14 Nov 2025 04:36:09 -0800 (PST) Date: Fri, 14 Nov 2025 12:36:08 +0000 In-Reply-To: Mime-Version: 1.0 References: X-Mailer: aerc 0.21.0 Message-ID: Subject: Re: [PATCH] mm/page_alloc: optimize lowmem_reserve max lookup using monotonicity From: Brendan Jackman To: fujunjie , Cc: , , , , , , , Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 3A7B7160009 X-Stat-Signature: 6iih5xbwohaip3cxobhajrgxips9xjcb X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1763123770-250224 X-HE-Meta: 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 gSHgvMGF IQXVLEGBzef8P6qJf1RgkRIUbnlODhlGAMGF9kN84+HGtNARY2K3aWGw+UyelRbikU9Xkik/aj7zCRL1N66ALtFTp5VOZF7VW4SO4EnADogIfS31KpakM6yp5/vNbpcj6j4TrTzoSXVwhR0sD2d9vGPpEraX4RLRZ6QKp9cncR1eKdxufLLoaxU4+hNyrvdz/cNxkKY7mPgw+ODKlGP5eEjcR7CNw7nD9ommepdlRz8xB/xVxniQKrPICiEp1QY9yvsbJAEbi2VRf3K8ne9/fL6XWY0XXfJEI2en1DTyXVK8lQGp1kbW2rPZ9noFwONbwkHFASR7w7iiml6BHuL/xONJcUXvhqWGGDIcp 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 Nov 14, 2025 at 10:40 AM UTC, fujunjie wrote: > Although this code is not on a hot path, the revised form is clearer Is it...? If people do think it is clearer, let's at least write the right comment in the right place. Instead of having one piece of code (calculate_totalreserve_pages()) describe at a distance the behaviour of another piece of code (setup_per_zone_lowmem_reserve()), let's describe an invariant of the data ("lowmem_reserve is monotonic, up to the first zero value"), at the site where the data is defined. I know sometimes in code this complex we do need these "spooky-action-at-a-distance" comments but this doesn't seem like one of those places to me.