From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 05B1933ADBA; Fri, 24 Apr 2026 18:26:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777055218; cv=none; b=FilIOHiqaozZnvaehVPCpLyEiJXvuU1p1iR3JvYzvB33SzWUqQszyXyK/5bpMCfSMaXTlwkR9bzv3/d4LQH1hDICg2dgCPS/YCQ+VPryXNaMQee5oIqcOgJz+TaHFuy66QxzuGXA20GKMRAxavnXL8J8prKxL6GVFUnmFArfZj4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777055218; c=relaxed/simple; bh=jE+zr5OC/t8vyDfTHUxqFb6gZ02duNQ6SztJCyxGuqE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=P9Li2xIxkjJL7nq5qHOP4MMFnoTyWwOKLKMCNUDm04062kSc0F4Dr21Rs7/1fpDCLjkKX8cqBpbkdm/qxz3KTX8sW8lH5V2KEs84GSj5WTiG8Ttn5TgDUAJWpOCZ5y7wt+5cMuXf/T+ZWXC8co5BroS6k2WuLwqEGUdo7rLJpw0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=u+/3vppJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="u+/3vppJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AEE05C19425; Fri, 24 Apr 2026 18:26:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777055217; bh=jE+zr5OC/t8vyDfTHUxqFb6gZ02duNQ6SztJCyxGuqE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=u+/3vppJBKOOpM3X1nw7OU1ci2VL3WwTteFLA23ZxyYPekT8sRH+NkSv9MryHCfw4 ByyOzoUTfzuyMEq/N4IgIhqN4WwV1+MnscD2fDaeHpW4WJ0ogBhoE1jWFzymx3Puf4 1rYxvxeXeOquKGwELqQ7LltCH/S5/mb5bogRPhMUmN96sLIjY7OgKyhUK/2zKbdJwB 7k5V7SoTeMWJpZTuTKG7gXD9PiZnMH7VOi2O4Cwbc8TdX+SnK+7XsIFe1yE9W9O8M+ JhrG9BNe+RbqZQeYPpuGmN5a9kscoHzq/1/9EA062MO0XLZDAiWAJcsgmVHQGIjBUw XW7ksSG+PnkYQ== Message-ID: <1dea839c-8a26-4fb4-b432-a866e31572ba@kernel.org> Date: Fri, 24 Apr 2026 20:26:49 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 4/7] mm: add page consistency checker implementation To: Sasha Levin Cc: akpm@linux-foundation.org, corbet@lwn.net, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, skhan@linuxfoundation.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Sasha Levin , Sanif Veeras , "Claude:claude-opus-4-7" References: <20260424140056.2094777-1-sashal@kernel.org> <20260424140056.2094777-5-sashal@kernel.org> <4b961a07-b72d-4c8a-ab49-23f61ed12b53@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/24/26 16:49, Sasha Levin wrote: > On Fri, Apr 24, 2026 at 04:25:41PM +0200, David Hildenbrand (Arm) wrote: >>> +    /* >>> +     * Size bitmaps to cover the full PFN range including any holes. >>> +     * Holes waste a few bits but a flat bitmap keeps the indexing >>> +     * trivial (pfn - min_pfn) and avoids additional data structures >>> +     * that would themselves be subject to corruption.  This matches >>> +     * the approach used by pageblock_flags. >>> +     */ >>> +    pc_state.min_pfn = PHYS_PFN(memblock_start_of_DRAM()); >>> +    pc_state.max_pfn = PHYS_PFN(memblock_end_of_DRAM()); >>> +    spanned_pfns = pc_state.max_pfn - pc_state.min_pfn; >>> +    if (!spanned_pfns || spanned_pfns > UINT_MAX) { >>> +        pr_err("PFN span %lu cannot be represented by bitmap APIs, feature >>> disabled\n", >>> +               spanned_pfns); >>> +        return; >>> +    } >>> + >>> +    pc_state.db.nbits = spanned_pfns; >>> + >>> +    bitmap_bytes = BITS_TO_LONGS(pc_state.db.nbits) * sizeof(unsigned long); >>> + >>> +    pr_info("Initializing: PFN range [%lu-%lu), %u bits (%zu KB per bitmap)\n", >>> +        pc_state.min_pfn, pc_state.max_pfn, pc_state.db.nbits, >>> +        bitmap_bytes / 1024); >>> + >>> +    /* Allocate primary bitmap (zeroed by memblock_alloc) */ >>> +    pc_state.db.bitmap[DUAL_BITMAP_PRIMARY] = >>> +        memblock_alloc(bitmap_bytes, SMP_CACHE_BYTES); >>> +    if (!pc_state.db.bitmap[DUAL_BITMAP_PRIMARY]) { >>> +        pr_err("Failed to allocate primary bitmap, feature disabled\n"); >>> +        return; >>> +    } >>> >> >> One bitmap that covers all sparse memory available at boot. >> >> Conclusion: Just horrible. > > Depends on who's looking at the code :) Or who generated that code ;) -- Cheers, David