On Wed 27-06-18 13:32:21, Michal Hocko wrote: > On Tue 26-06-18 18:48:25, Jan Kara wrote: > > On Tue 26-06-18 15:47:57, Michal Hocko wrote: > > > On Mon 18-06-18 12:21:46, Dan Williams wrote: > > > [...] > > > > I do think we should explore a page flag for pages that are "long > > > > term" pinned. Michal asked for something along these lines at LSF / MM > > > > so that the core-mm can give up on pages that the kernel has lost > > > > lifetime control. Michal, did I capture your ask correctly? > > > > > > I am sorry to be late. I didn't ask for a page flag exactly. I've asked > > > for a way to query for the pin to be temporal or permanent. How that is > > > achieved is another question. Maybe we have some more spare room after > > > recent struct page reorganization but I dunno, to be honest. Maybe we > > > can have an _count offset for these longterm pins. It is not like we are > > > using the whole ref count space, right? > > > > Matthew had an interesting idea to pull pinned pages completely out from > > any LRU and reuse that space in struct page for pinned refcounts. From some > > initial investigation (read on elsewhere in this thread) it looks doable. I > > was considering offsetting in refcount as well but on 32-bit architectures > > there's not that many bits that I'd be really comfortable with that > > solution... > > I am really slow at following up this discussion. The problem I would > see with off-lru pages is that this can quickly turn into a weird > reclaim behavior. Especially when we are talking about a lot of memory. > It is true that such pages wouldn't be reclaimable directly but could > poke them in some way if we see too many of them while scanning LRU. > > Not that this is a fundamental block stopper but this is the first thing > that popped out when thinking about such a solution. Maybe it is a good > start though. > > Appart from that, do we really care about 32b here? Big DIO, IB users > seem to be 64b only AFAIU. IMO it is a bad habit to leave unpriviledged-user-triggerable oops in the kernel even for uncommon platforms... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
