From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 446301BD9C9 for ; Fri, 14 Nov 2025 12:36:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763123772; cv=none; b=HfoduYd2H/1mtCsaXF0grI7baUesVIuACmhB5AuCNsGzHIRsXirs7HQYBwNxeS18IS4s+vz3+6Wb1EXXDeZia8rrUB2WW9DuzX/lTx7+xI0CsQK7WgAhO9m4QuOzvAzLZ3/GmVGVv1CEke/jQjW5tjoEVnRUhs6iCV9JqQqtuCA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763123772; c=relaxed/simple; bh=IxQT1ueN0Bj88cVZcCku+VDcMMej+3QPEoT+7oXlEUc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=lQkbhcPWLy+jws3ShEgLFQDTkoQ8GGBWcFsV4XW+RM4hNMzVxYXKm5biEK+Cosfs/hOoK9zj0/IWhbURqbgHaTO9a59vFX5HGIGDcFl0U6cxPXSnjmJsy/WUQFtEy9lzvfUY8HNmxOU5wfxJ9burt6R22bxLrD1HY40FAaETAqs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jackmanb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=aUJLNzdi; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jackmanb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="aUJLNzdi" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-477212937eeso11687405e9.2 for ; Fri, 14 Nov 2025 04:36:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1763123769; x=1763728569; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=IxQT1ueN0Bj88cVZcCku+VDcMMej+3QPEoT+7oXlEUc=; b=aUJLNzdiYYvCamEvoYOF8RwJljQso3TD6mEXfiRw85Ao61UXWFojFeuQLA+rg/3kKo 5JtT82DsTAzYYBoWMrmQzJ+zm6/Es7xPLR1dgtoXOQNDmVblvM+dZs60kvnGrSleM8K+ wv6ppK+SjG7wjK6eKguNKOMRUckrnj1/3hz4inwGUhady76jJWN8yyjspaSvuDMdtoS0 PFydfgWhVBbvW2gc/RkgV9c38n4GXwwX87vMIayCN0+Ah1XweDZvBanvbmFqqVRF6A1a 1/UxqPmLwNpKG4TujAC8HwnXUEM8F8R9eYVxD4P20/ZAp8nWuLbTSTaObxqbziJuNzEY Swwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1763123769; x=1763728569; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=IxQT1ueN0Bj88cVZcCku+VDcMMej+3QPEoT+7oXlEUc=; b=sx1Nt4Erp3y4GnF8Y60Kt6SlXIr6OTutrNOlk/o3gDGisntqaDxtbPl0qAiS/Mbd81 zYyMokbCcwSJ/wo/UTO9YwDNtP3AGo/hYHuNR5xYT+LOSazMpY0QfIz9deaPrl8AGcuB BPLNkCqUtxDPHCXtgZNu3WlMOZJz5eNoneimYQz1TuDoqPxWXfXrXfIMXy82+YqUnzvG wRJ0U916IBnxIpvmX723sq17MhJmkcSojEqIAaFKPMedqbwDXtdJo+STvy0BZUjimj7E 2/XxPQl+YGgPImgx8QhScutUWjXk1TXphbD5cNqGjoTbi3sb8BZSYv8RwpxKNJbdYMy/ AvmA== X-Forwarded-Encrypted: i=1; AJvYcCX+LNKj7QuFtAuSEKuYDnL1P4b90k36odVX61IU6lMFnHV0Q3vQ6s0/8Q2cAUghX9XA97zFVl3I33HHW1k=@vger.kernel.org X-Gm-Message-State: AOJu0YwO7D6BnBqyDzOxcnd7nTQ9XtoR1tgzX/gxxwzYuQcH9cWL9b25 PKhQsbBuRrr0ZmUXppptJtctH1QVuJnD9gYnTcbU/dyo4EXQij4GgvGBWIn2Vi8TBX6lFegPJnv 050b8PlwWUcE+JQ== 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: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" 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.