On Thu 12-09-19 13:24:25, Kirill A. Shutemov wrote: > On Thu, Sep 12, 2019 at 11:19:25AM +0200, Michal Hocko wrote: > > On Wed 11-09-19 08:12:03, Alexander Duyck wrote: > > > On Wed, Sep 11, 2019 at 4:36 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Tue 10-09-19 14:23:40, Alexander Duyck wrote: > > > > [...] > > > > > We don't put any limitations on the allocator other then that it needs to > > > > > clean up the metadata on allocation, and that it cannot allocate a page > > > > > that is in the process of being reported since we pulled it from the > > > > > free_list. If the page is a "Reported" page then it decrements the > > > > > reported_pages count for the free_area and makes sure the page doesn't > > > > > exist in the "Boundary" array pointer value, if it does it moves the > > > > > "Boundary" since it is pulling the page. > > > > > > > > This is still a non-trivial limitation on the page allocation from an > > > > external code IMHO. I cannot give any explicit reason why an ordering on > > > > the free list might matter (well except for page shuffling which uses it > > > > to make physical memory pattern allocation more random) but the > > > > architecture seems hacky and dubious to be honest. It shoulds like the > > > > whole interface has been developed around a very particular and single > > > > purpose optimization. > > > > > > How is this any different then the code that moves a page that will > > > likely be merged to the tail though? > > > > I guess you are referring to the page shuffling. If that is the case > > then this is an integral part of the allocator for a reason and it is > > very well obvious in the code including the consequences. I do not > > really like an idea of hiding similar constrains behind a generic > > looking feature which is completely detached from the allocator and so > > any future change of the allocator might subtly break it. > > I don't necessary follow why shuffling is more integral to page allocator > than reporting would be. It's next to shutffle.c under mm/ and integrated > in a simillar way. The main difference from my understanding is that the page reporting is a more generic looking feature which might grow different users over time yet there is a hardcoded set of restrictions to the allocator. Page shuffling is an integral part of the allocator without any other visibility outside. -- Michal Hocko SUSE Labs
