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b=DofXVLTZOLJBasreFFoD4GB529ZJhR9p9hi9FJzzR7k3ya8vwqlS/HZoCOka8sOVP /PiRxL7CrMv6+PHpWjGyPK3rhjRX+R/DAzhh1hBu5Vdlds7d1DNtIsUZ3gaaNJjQzI U3lruPBer07yxkOFicQRfyTZG40sAEGmjBnES58hOCWky276BbHNkvuPG0B/cApuSC sDPcYDMn++TNz+JgIG17HhBOwZlJgpsznHNWxyYqgYE9FYEIOUaOOBwJkYSTeMG6gs ZFkTDa1Ex62JyGwnBDRJ87XhmiVu/CvXRhiS6wA40BHd3G+sBRYaor0qiQFSpGlJxF qnggDM0+yg0NQ== Message-ID: <4b961a07-b72d-4c8a-ab49-23f61ed12b53@kernel.org> Date: Fri, 24 Apr 2026 16:25:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 4/7] mm: add page consistency checker implementation To: Sasha Levin , akpm@linux-foundation.org, corbet@lwn.net Cc: 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: zf44xcucodnezt5pp8gx1sjuqgff9jbf X-Rspamd-Queue-Id: 3B3B84000B X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1777040750-872518 X-HE-Meta: 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 edGQJttS nvRVLDLr4NyNqhYLdi+qGqUYgX1dIy5WWu3rLWvCmKldFprBiMJAbWPbhbEDjMzuhJQwnK7TpkGRFP93aLaO9xQ3cBhfFjN73ShjXqXghtGQRB20NiFuq/IjvDpN9YZWc9x2MAnMOUzsyWLUTnYIFfFQHm5aZloRoIoS7b06aaRF0Tw55IUzpzGaau20vTj+mSykr9rdIk5AAMEhfm66t1/Hcud9xadfymZAQHuiCOn5vXikrAc5lGd27k/rNMvAqJz5w Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > + /* > + * 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. -- Cheers, David