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b=YEvjjIsdeQS+VXWfT62+1y6ZmLHQhBQdO5DzyWVgc/cNGTUnFYLgt7W0n49KP3x0I 2qnGRwrRfk8gzhpj6CpJaByqIkuiO4f5E5bie1iequdnJvG6CtJlhk0h+NrqEyKJ+M aR84lskvYfWgFFArVhkhTFgmbo23eeMRV+feqgwkTaOyJuQmqK6HtBVupdmNG3ZAET gi3+NqBHS6maLsdRH8d5jI8rglQ6sRQ+htHYMUSRoYP64KJ05EZSniF1vSbHIqmde8 M3EfvChB9r7SD6Ef3E+wnOYZOHDvvVu4xLs5mF2ZLndwj3DISKfdwXsH/CzJXrpwxe dIxmE0xi3Oa4A== From: Pratyush Yadav 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, rppt@kernel.org, tj@kernel.org, jasonmiu@google.com, dmatlack@google.com, skhawaja@google.com Subject: Re: [PATCH v3 2/3] liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE In-Reply-To: <20251021000852.2924827-3-pasha.tatashin@soleen.com> (Pasha Tatashin's message of "Mon, 20 Oct 2025 20:08:51 -0400") References: <20251021000852.2924827-1-pasha.tatashin@soleen.com> <20251021000852.2924827-3-pasha.tatashin@soleen.com> Date: Wed, 22 Oct 2025 12:25:08 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam05 X-Stat-Signature: rb8u8gk41m6j9r9azkj4qjwk4qaymecp X-Rspam-User: X-Rspamd-Queue-Id: 004DAC0012 X-HE-Tag: 1761128712-660971 X-HE-Meta: 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 HuShBZqn W+sZiVE+umPVkxMuzHqU1aV88BI5zFXzOuPDXsx08BKP3IHwhScJnXTrExbq9pjELy6gswtCw2goNvukhQ0AhO73CNqv5AQLp9Tbthifk48QXqSYkF2Lsmdx5811DIE00nYciJg6ux+ECyf6p36bA7QX2n0nmgD9Jvn441++wIC+0nKQsM/EGViw+ImbzjVQLjJNQBBmWZ06tyGjrG2wEvMIzpuhW3K1s1Mr/5cRtyNCn9+iuDpKwHldfXp+LPc00Fe6PfygYJV/xS5g+DY09WT45G3+WxwRRvP5aA2BHGEr6Pco= 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 Mon, Oct 20 2025, Pasha Tatashin wrote: > KHO memory preservation metadata is preserved in 512 byte chunks which > requires their allocation from slab allocator. Slabs are not safe to be > used with KHO because of kfence, and because partial slabs may lead > leaks to the next kernel. Change the size to be PAGE_SIZE. > > The kfence specifically may cause memory corruption, where it randomly > provides slab objects that can be within the scratch area. The reason > for that is that kfence allocates its objects prior to KHO scratch is > marked as CMA region. > > 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. > > Signed-off-by: Pasha Tatashin Reviewed-by: Pratyush Yadav [...] -- Regards, Pratyush Yadav