On Tue, Aug 27, 2019 at 02:09:23PM +0200, Michal Hocko wrote: > On Tue 27-08-19 14:01:56, Vlastimil Babka wrote: > > On 8/27/19 1:02 PM, Kirill A. Shutemov wrote: > > > On Tue, Aug 27, 2019 at 08:01:39AM +0200, Michal Hocko wrote: > > >> On Mon 26-08-19 16:15:38, Kirill A. Shutemov wrote: > > >>> > > >>> Unmapped completely pages will be freed with current code. Deferred split > > >>> only applies to partly mapped THPs: at least on 4k of the THP is still > > >>> mapped somewhere. > > >> > > >> Hmm, I am probably misreading the code but at least current Linus' tree > > >> reads page_remove_rmap -> [page_remove_anon_compound_rmap ->\ deferred_split_huge_page even > > >> for fully mapped THP. > > > > > > Well, you read correctly, but it was not intended. I screwed it up at some > > > point. > > > > > > See the patch below. It should make it work as intened. > > > > > > It's not bug as such, but inefficientcy. We add page to the queue where > > > it's not needed. > > > > But that adding to queue doesn't affect whether the page will be freed > > immediately if there are no more partial mappings, right? I don't see > > deferred_split_huge_page() pinning the page. > > So your patch wouldn't make THPs freed immediately in cases where they > > haven't been freed before immediately, it just fixes a minor > > inefficiency with queue manipulation? > > Ohh, right. I can see that in free_transhuge_page now. So fully mapped > THPs really do not matter and what I have considered an odd case is > really happening more often. > > That being said this will not help at all for what Yang Shi is seeing > and we need a more proactive deferred splitting as I've mentioned > earlier. It was not intended to fix the issue. It's fix for current logic. I'm playing with the work approach now. -- Kirill A. Shutemov
