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b=n4kzHdFkS93dzBf/0sB8LNKsZ13c/FMalJ7qio3iOrsEsZ7KoSTLEFgzargeBcq+d 91GPSZFDSYKszIoGvVWUcz4DBGBcNf/fGVAheD01TE6yF3/oM/FF2HA4YprwGHF8YC HmX2P/Ex08ZqCO8bd/tQoXuXA6iN8Z2uBkWM69wbTQhDPR3Q0Nmfh4pfyzsuEO9W1f Lp/Fnq+oVLRj8WQ1OBEpzbF5vmN6zREJhq3cBavYShrRFJiYGAYG+hxtZAiRVGG9dA Za/4kBiS4LglmJRU758hdOa5ybFwfbSnO3RsKBwcDgP/VN9eQX/4DO3RF9ii8tmYSd 2szB50df5VyvQ== Message-ID: Date: Sat, 25 Apr 2026 07:51:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 0/7] mm: dual-bitmap page allocator consistency checker To: Sasha Levin , "Vlastimil Babka (SUSE)" Cc: akpm@linux-foundation.org, corbet@lwn.net, ljs@kernel.org, Liam.Howlett@oracle.com, 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 References: <20260424140056.2094777-1-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-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 6923A1A0011 X-Stat-Signature: kitdupunpjphk8abdd7fcu55ybeyqweq X-Rspam-User: X-HE-Tag: 1777096279-266459 X-HE-Meta: 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 HiGfx+lo K6Uzh1beM5GioRf2Ou7IZzGbQ7TWIw/iKzSCVibPLZCx/5qXgh3LC9P/aHXecrpNO4z3XSPWaS+TCOYoQCUTKgeQWoA2qIpAn7qMeEPuhqhSz6QxfAhUqUuSnuE2EqBFsAlV83QrDotnADmDRaK/0Fz0hrTWUU5PEE5GXeaVe14lYhfmSshEIZmNJ0lJ5lSpTzK/OHq7mT8JJ8ROJlALnxdb2ijYJ1XMZoZKcAIShGKmxf9T9WywJK4t1b4m9bya+gEuwYSTZfRpz61TL5s9vAbZou68TOzJSQJnz Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/24/26 18:25, Sasha Levin wrote: > On Fri, Apr 24, 2026 at 05:42:53PM +0200, Vlastimil Babka (SUSE) wrote: >> On 4/24/26 16:00, Sasha Levin wrote: >>> Existing memory debugging tools - KASAN, KFENCE, page_poisoning - detect >>> access violations and content corruption, but none of them can detect >>> silent corruption in the page allocator's own metadata. If a hardware >>> bit flip corrupts an allocation bitmap, the allocator hands out a page >> >> An allocation what? The page allocator is a buddy allocator, it has no >> bitmap to track free/allocated state of pages? > > You're right, the cover letter is misleading there. Buddy doesn't use a bitmap: > PageBuddy lives in page_type, the free list is a list, and page->private holds > the order. The dual-bitmap is new metadata the feature adds, maintained from > the alloc/free hooks. Given that you have PageBuddy (first "bit"), could we use a second bit in page_ext? -- Cheers, David