On Wed, Jul 10, 2019 at 09:47:19PM +0200, Michal Hocko wrote: > On Wed 10-07-19 20:53:56, Minchan Kim wrote: > > On Wed, Jul 10, 2019 at 01:16:22PM +0200, Michal Hocko wrote: > > > On Wed 10-07-19 19:48:09, Minchan Kim wrote: > > > > On Tue, Jul 09, 2019 at 11:55:19AM +0200, Michal Hocko wrote: > > > [...] > > > > > I am still not convinced about the SWAP_CLUSTER_MAX batching and the > > > > > udnerlying OOM argument. Is one pmd worth of pages really an OOM risk? > > > > > Sure you can have many invocations in parallel and that would add on > > > > > but the same might happen with SWAP_CLUSTER_MAX. So I would just remove > > > > > the batching for now and think of it only if we really see this being a > > > > > problem for real. Unless you feel really strong about this, of course. > > > > > > > > I don't have the number to support SWAP_CLUSTER_MAX batching for hinting > > > > operations. However, I wanted to be consistent with other LRU batching > > > > logic so that it could affect altogether if someone try to increase > > > > SWAP_CLUSTER_MAX which is more efficienty for batching operation, later. > > > > (AFAIK, someone tried it a few years ago but rollback soon, I couldn't > > > > rebemeber what was the reason at that time, anyway). > > > > > > Then please drop this part. It makes the code more complex while any > > > benefit is not demonstrated. > > > > The history says the benefit. > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/patch/?id=d37dd5dcb955dd8c2cdd4eaef1f15d1b7ecbc379 > > Limiting the number of isolated pages is fine. All I am saying is that > SWAP_CLUSTER_MAX is an arbitrary number same as 512 pages for one PMD as > a unit of work. Both can lead to the same effect if there are too many > parallel tasks doing the same thing. > > I do not want you to change that in the reclaim path. All I am asking > for is to add a bathing without any actual data to back that because > that makes the code more complex without any gains. I understand what you meant and I'm really one to make code simple. However, my concern was that we have isolated by SWAP_CLUSTER_MAX(32 pages) for other path(reclaim/compaction) so I want to be consistent with others. If you think that the consistency(IOW, others are 32 limit but here 256 limit) is no helpful this case, I don't have any strong opinion. Let's drop the part. I will add it into description, then. Thanks. > -- > Michal Hocko > SUSE Labs
