On Tue, Dec 20, 2022 at 08:14:15PM +0800, Baoquan He wrote: > Hmm, for the two kinds of vm_map_ram areas, their code paths are > different. for unmapping vmap_block vm_map_ram, it goes through > vb_free(). I can only do the clearing in free_vmap_block(). > > -->vm_unmap_ram() > -->vb_free() > -->free_vmap_block() > > For non vmap_block vm_map_ram area, I can do the clearing in > vm_unmap_ram(). > -->vm_unmap_ram() > -->__find_vmap_area() > -->free_unmap_vmap_area() > > As said earlier, clearing va->flags when unmap vm_map_ram area, or > clearing va->vm in remove_vm_area(), these have better be done. > However, not clearing them won't cause issue currently. Because the > old vmap_area is inserted into free_vmap_area_root, when we allocate a > new vmap_area through alloc_vmap_area(), we will get q new vmap_area > from vmap_area_cachep, the old va->flags or va->vm won't be carried into > the new vmap_area. Clearing them is a good to have, just in case. > Sure, this is more so about avoiding confusion and perhaps some future change which might not take into account that flag state could be invalid. I guess logically speaking, this is still a block when you are unmapping ram, so it's not unreasonable to retain the VMAP_BLOCK flag. In that case I'd say we're good simply clearing VMAP_RAM here. Thanks for the explanations! > Rethinking about this, I may need to do the clearing when freeing > vmap_block. Otherwise, people will be confused why the clearing is not > done. > > @@ -1815,6 +1815,7 @@ static void free_vmap_area_noflush(struct vmap_area *va) > > spin_lock(&vmap_area_lock); > unlink_va(va, &vmap_area_root); > + va->flags = 0; > spin_unlock(&vmap_area_lock); > > nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >> > That sounds like a good idea!
