On Fri 09-08-19 10:12:48, Vlastimil Babka wrote: > On 8/9/19 12:59 AM, John Hubbard wrote: > >>> That's true. However, I'm not sure munlocking is where the > >>> put_user_page() machinery is intended to be used anyway? These are > >>> short-term pins for struct page manipulation, not e.g. dirtying of page > >>> contents. Reading commit fc1d8e7cca2d I don't think this case falls > >>> within the reasoning there. Perhaps not all GUP users should be > >>> converted to the planned separate GUP tracking, and instead we should > >>> have a GUP/follow_page_mask() variant that keeps using get_page/put_page? > >>> > >> > >> Interesting. So far, the approach has been to get all the gup callers to > >> release via put_user_page(), but if we add in Jan's and Ira's vaddr_pin_pages() > >> wrapper, then maybe we could leave some sites unconverted. > >> > >> However, in order to do so, we would have to change things so that we have > >> one set of APIs (gup) that do *not* increment a pin count, and another set > >> (vaddr_pin_pages) that do. > >> > >> Is that where we want to go...? > >> > > We already have a FOLL_LONGTERM flag, isn't that somehow related? And if > it's not exactly the same thing, perhaps a new gup flag to distinguish > which kind of pinning to use? Agreed. This is a shiny example how forcing all existing gup users into the new scheme is subotimal at best. Not the mention the overal fragility mention elsewhere. I dislike the conversion even more now. Sorry if this was already discussed already but why the new pinning is not bound to FOLL_LONGTERM (ideally hidden by an interface so that users do not have to care about the flag) only? -- Michal Hocko SUSE Labs
