On Tue, Sep 22, 2020 at 05:09:10PM +0200, Christoph Hellwig wrote: > On Tue, Sep 22, 2020 at 04:06:03PM +0100, Matthew Wilcox wrote: > > I don't think it makes sense to list all vmalloc-style allocators here. > > It won't be updated by people who add new variations. How about this? > > > > * Free the virtually continuous memory area starting at @addr, as > > * obtained from one of the vmalloc() family of APIs. This will > > * usually also free the physical memory underlying the virtual > > * allocation, but that memory is reference counted, so it will not > > * be freed until the last user goes away. > > * > > * If @addr is NULL, no operation is performed. > > > > I'm trying to strike a balance between being accurate and not requiring > > device driver authors to learn all about struct page. I may be too > > close to the implementation to write good documentation for it. > > I think the above is sensible, but not enough. vmap really needs to > be treated special, as by default area->pages for vmap is NULL. So > for vfree to be useful on a vmap mapping, the callers needs to > manually set it up by poking into the internals. Actually, I think > we really want another API rather than vmap for that. Let me respin > my series to include that. I've been thinking about somethng like: void *vmap_mapping(struct address_space *mapping, pgoff_t start, unsigned long len); but it doesn't quite work for the shmem cases because they need to use shmem_read_mapping_page_gfp() instead of ->readpage. I'd also want it to work for DAX, but I don't have a user for that yet so it's hard to justify adding it. I have ideas for making shmem/tmpfs work more like other filesystems, so we don't need shmem_read_mapping_page_gfp() but there are only so many hours in the day.
