When vrealloc() shrinks an allocation and the new size crosses a page boundary, unmap and free the tail pages that are no longer needed. This reclaims physical memory that was previously wasted for the lifetime of the allocation. The heuristic is simple: always free when at least one full page becomes unused. Huge page allocations (page_order > 0) are skipped, as partial freeing would require splitting. Allocations with VM_FLUSH_RESET_PERMS are also skipped, as their direct-map permissions must be reset before pages are returned to the page allocator, which is handled by vm_reset_perms() during vfree(). Additionally, allocations with VM_USERMAP are skipped because remap_vmalloc_range_partial() validates mapping requests against the unchanged vm->size; freeing tail pages would cause vmalloc_to_page() to return NULL for the unmapped range. To protect concurrent readers, the shrink path uses Node lock to synchronize before freeing the pages. Finally, we notify kmemleak of the reduced allocation size using kmemleak_free_part() to prevent the kmemleak scanner from faulting on the newly unmapped virtual addresses. The virtual address reservation (vm->size / vmap_area) is intentionally kept unchanged, preserving the address for potential future grow-in-place support. Link: https://lore.kernel.org/20260519-vmalloc-shrink-v14-4-70b96ee3e9c9@zohomail.in Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in> Suggested-by: Danilo Krummrich <dakr@kernel.org> Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Cc: Alice Ryhl <aliceryhl@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>