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b=nd0ZDtoEuFOr+zoWoSMvb4XzMTaYscSYSJMWOmFsE7Qxub0TAoPqFHR7bX9fFW39X LkhOKYUgdo9ZFYeks2Kagf/RlYbLwy6Q7L9Djw0+WcKn3fC+iqd9r5/tiPurqJkLxo FIxmJCbWLpvmL4Gf688hl/e1aM83KdUe1K7pRblXH8Jb5FAdO9XFL2C/Z0bMYcHcEz DHIEyTGuFAsHD2XGYXNbQAxg5XG2KV2tG2g87NRhRkQiItfHBFGAXiVsr0M6SeNDej PWhCgW8HIBEKYkVZUYhdRVf4s3CL4kA+9/Mb7bVN0j/zXlbEI6Rkm6hwBKkCBjcWjz 2JK74TNLMXU8g== Date: Mon, 20 Oct 2025 11:03:27 +0300 From: Mike Rapoport To: Pasha Tatashin Cc: akpm@linux-foundation.org, brauner@kernel.org, corbet@lwn.net, graf@amazon.com, jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, masahiroy@kernel.org, ojeda@kernel.org, pratyush@kernel.org, rdunlap@infradead.org, tj@kernel.org, jasonmiu@google.com, dmatlack@google.com, skhawaja@google.com Subject: Re: [PATCH v6 09/10] liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE Message-ID: References: <20251018171756.1724191-1-pasha.tatashin@soleen.com> <20251018171756.1724191-10-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251018171756.1724191-10-pasha.tatashin@soleen.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E7A9540004 X-Stat-Signature: kzfjukgyj79cfstxo6dwde3uc4n7usfz X-Rspam-User: X-HE-Tag: 1760947417-743400 X-HE-Meta: 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 PdW47Uyo xkb9S X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Oct 18, 2025 at 01:17:55PM -0400, Pasha Tatashin wrote: > Metadata is preserved via 512-bytes, which requires using slabs. Slabs KHO memory preservation metadata is preserved in 512 byte chunks which requires their allocation from slab allocator. > are not safe to be used with KHO because of kfence, and because partial Please add more details why kfence is not safe here. > slabs may lead leaks to the next kernel. Change the size to be > PAGE_SIZE. > > While this change could potentially increase metadata overhead on > systems with sparsely preserved memory, this is being mitigated by > ongoing work to reduce sparseness during preservation via 1G guest > pages. Furthermore, this change aligns with future work on a stateless > KHO, which will also use page-sized bitmaps for its radix tree metadata. With the stateless memory preservation there would be no problem with kfence, right? Maybe we should accelerate the stateless preservation work? > Signed-off-by: Pasha Tatashin -- Sincerely yours, Mike.