On Wed 11-09-19 08:08:38, Michael S. Tsirkin wrote: > On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko 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. > > > > I remember that there was an attempt to report free memory that provided > > a callback mechanism [1], which was much less intrusive to the internals > > of the allocator yet it should provide a similar functionality. Did you > > see that approach? How does this compares to it? Or am I completely off > > when comparing them? > > > > [1] mostly likely not the latest version of the patchset > > http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@xxxxxxxxx > > Linus nacked that one. He thinks invoking callbacks with lots of > internal mm locks is too fragile. I would be really curious how much he would be happy about injecting other restrictions on the allocator like this patch proposes. This is more intrusive as it has a higher maintenance cost longterm IMHO. -- Michal Hocko SUSE Labs
