On Thu, Apr 21, 2022 at 11:01 PM Nicholas Piggin <npiggin@xxxxxxxxx> wrote:
>
> Huge vmalloc higher-order backing pages were allocated with __GFP_COMP
> in order to allow the sub-pages to be refcounted by callers such as
> "remap_vmalloc_page [sic]" (remap_vmalloc_range).
>
> However a similar problem exists for other struct page fields callers
> use, for example fb_deferred_io_fault() takes a vmalloc'ed page and
> not only refcounts it but uses ->lru, ->mapping, ->index. This is not
> compatible with compound sub-pages.
>
> The correct approach is to use split high-order pages for the huge
> vmalloc backing. These allow callers to treat them in exactly the same
> way as individually-allocated order-0 pages.
This patch looks ObviouslyCorrect(tm), and you even reproduced the
fbdev problem.
Applied.
Linus
