On Wed, Sep 09, 2020 at 09:01:14AM +0100, Christoph Hellwig wrote: > I really don't think this approach is any good. You workaround > a deficiency in the pin_user_pages API in one particular caller for > one particular use case. > > I think you'd rather want either: > > (1) a FOLL_HUGEPAGE flag for the pin_user_pages API family that returns > a single struct page for any kind of huge page, which would also > benefit all kinds of other users rather than adding these kinds of > hacks to vfio.
This seems to be similar to a flag I added last week to pagecache_get_page() called FGP_HEAD: + * * %FGP_HEAD - If the page is present and a THP, return the head page + * rather than the exact page specified by the index. I think "return the head page" is probably what we want from what I understand of this patch. The caller can figure out the appropriate bv_offset / bv_len for a bio_vec, if that's what they want to do with it. http://git.infradead.org/users/willy/pagecache.git/commitdiff/ee88eeeb6b0f35e95ef82b11dfc24dc04c3dcad8 is the exact commit where I added that, but it depends on a number of other patches in this series: http://git.infradead.org/users/willy/pagecache.git/shortlog I'm going to send out a subset of patches later today which will include that one and some others. I haven't touched the GUP paths at all in that series, but it's certainly going to make THPs (of various sizes) much more present in the system.
