On Tue 22-10-19 09:56:27, Oscar Salvador wrote: > On Mon, Oct 21, 2019 at 04:06:19PM +0200, Michal Hocko wrote: > > On Mon 21-10-19 15:48:48, Oscar Salvador wrote: > > > We can only perform actions on LRU/Movable pages or hugetlb pages. > > > > What would prevent other pages mapped via page tables to be handled as > > well? > > What kind of pages? Any pages mapped to the userspace. E.g. driver memory which is not on LRU. > I mean, I guess it could be done, it was just not implemented, and I > did not want to add more "features" as my main goal was to re-work > the interface to be more deterministic. Fair enough. One step at the time sounds definitely good > > > 1) we would need to hook in enqueue_hugetlb_page so the page is not enqueued > > > into hugetlb freelists > > > 2) when trying to free a hugetlb page, we would need to do as we do for gigantic > > > pages now, and that is breaking down the pages into order-0 pages and release > > > them to the buddy (so the check in free_papges_prepare would skip the > > > hwpoison page). > > > Trying to handle a higher-order hwpoison page in free_pages_prepare is > > > a bit complicated. > > > > I am not sure I see the problem. If you dissolve the hugetlb page then > > there is no hugetlb page anymore and so you make it a regular high-order > > page. > > Yes, but the problem comes when trying to work with a hwpoison high-order page > in free_pages_prepare, it gets more complicated, and when I weigthed > code vs benefits, I was not really sure to go down that road. > > If we get a hwpoison high-order page in free_pages_prepare, we need to > break it down to smaller pages, so we can skip the "bad" to not be sent > into buddy allocator. But we have destructors for compound pages. Can we do the heavy lifting there? > > If the page is free then it shouldn't pin the memcg or any other state. > > Well, it is not really free, as it is not usable, is it? Sorry I meant to say the page is free from the memcg POV - aka no task from the memcg is holding a reference to it. The page is not usable for anybody, that is true but no particular memcg should pay a price for that. This would mean that random memcgs would end up pinned for ever without a good reason. -- Michal Hocko SUSE Labs
