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Tue, 6 Jan 2026 15:48:40 -0800 (PST) From: Laveesh Bansal To: dakr@kernel.org Cc: linux-mm@kvack.org Subject: vrealloc() shrink TODO Date: Tue, 6 Jan 2026 23:48:39 +0000 Message-ID: <20260106234839.586018-1-laveeshb@laveeshbansal.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Queue-Id: 6ECFD80009 X-Stat-Signature: fcbyr5z4dnqp9mt985o6yrkmb8gu6o9q X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1767743326-590373 X-HE-Meta: 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 Rcu3v8wn SNSicXeX8d9L/A+xnROkR8mfUOrLo6IEiP9MiWFGjvUhPZmmEHRZWfWv3yI7fIS5jxpqleMD44p2izCktIuyZDZlN4+Swm9V6aKYR/75o2rGLM+zT2p1yk6iie1ZEWKqL9/ziTJOmTNDufg9StFsM0mGWy+PGQyQsI4i8P2Xqv25hp+zdf3/4ucIk+utmyQ0gV1EFID+P+01k6zTryDgkxoLY7QUVRnTjMaqsIkTnXzw38U2OvCLfdfYR9UOHErtWQP6wbTB4FnRJcJfalX02peOxlh/huJ6KjLrp274W0I8712Xnws19KHvBYCThVxPD4MgJ41+7uM7FtfE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Danilo, I came across the TODO you left in vrealloc_node_align_noprof() (mm/vmalloc.c:4317) about shrinking the vm_area when reallocating to a smaller size. I'd like to work on this if it's still relevant. I wanted to check if this approach makes sense: keep the virtual address range unchanged, unmap pages from the end using vunmap_range(), free them, and update nr_pages and memcg accounting. This would avoid vmap_area allocator complexity while still reclaiming physical memory. One thing I'm not sure about: for huge page allocations (page_order > 0), partial unmapping seems problematic - should shrink just be skipped in that case? A few questions: 1. Is this optimization still wanted? 2. Does the approach above make sense, or is there a better way? 3. Any preference on the shrink heuristic? 4. Anything else I should watch out for? Thanks, Laveesh