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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 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 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9DB891C0013 X-Stat-Signature: mzn7ob3j87dkus7tksgese1jxx1tjdk1 X-HE-Tag: 1777055218-250068 X-HE-Meta: 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 zQsweGGJ 6kEMaZVowPqkCLLnIGC7b1kgUUgvwTLbvl58hIl+Ntse7q8iR2tE0cvxllTArY8k+GZ5X3BUxLpcW1Be1aApFNZpWpP4yK/HSfl1mBgijVzCbzig8MMrW8oUyNk+5XtxceQipR+Cqgx8jKVYsnBMsE/KsXiqnW5HWyUG66UawTvblnEiX3GMxVMU3WDuXa4GJ8y6u1SUqRL9tm0akah1yBsJBwiacwYrhJVs9Y8heMppobMKSyxUoRssBpz56qvir7v2Q3uDi9E85MwHrzRYmmYtbeuGUt+9RjuVm Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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