On Wed, Jun 27, 2018 at 09:05:39AM -0700, Linus Torvalds wrote: > [ Sorry for slow reply, my travels have made a mess of my inbox ] > > On Mon, Jun 25, 2018 at 6:55 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > Linus, do you think it would be ok to have get_from_free_page_list > > actually pop entries from the free list and use them as the buffer > > to store PAs? > > Honestly, what I think the best option would be is to get rid of this > interface *entirely*, and just have the balloon code do > > #define GFP_MINFLAGS (__GFP_NORETRY | __GFP_NOWARN | > __GFP_THISNODE | __GFP_NOMEMALLOC) > > struct page *page = alloc_pages(GFP_MINFLAGS, MAX_ORDER-1); > > which is not a new interface, and simply removes the max-order page > from the list if at all possible. > > The above has the advantage of "just working", and not having any races. > > Now, because you don't want to necessarily *entirely* deplete the max > order, I'd suggest that the *one* new interface you add is just a "how > many max-order pages are there" interface. So then you can query > (either before or after getting the max-order page) just how many of > them there were and whether you want to give that page back. > > Notice? No need for any page lists or physical addresses. No races. No > complex new functions. > > The physical address you can just get from the "struct page" you got. > > And if you run out of memory because of getting a page, you get all > the usual "hey, we ran out of memory" responses.. > > Wouldn't the above be sufficient? > > Linus I think so, thanks! Wei, to put it in balloon terms, I think there's one thing we missed: if you do manage to allocate a page, and you don't have a use for it, then hey, you can just give it to the host because you know it's free - you are going to return it to the free list. -- MST
