On Wed, Jan 04, 2017 at 01:40:24AM -0500, Johannes Weiner wrote: > Hi, > > On Wed, Dec 28, 2016 at 03:57:32PM +0100, Michal Hocko wrote: > > This is something I would be interested to discuss even though I am not > > working on it directly. Sorry if I hijacked the topic from those who > > planned to post them. > > > > It seems that the time to reconsider our approach to the swap storage is > > come already and there are multiple areas to discuss. I would be > > interested at least in the following > > 1) anon/file balancing. Johannes has posted some work already and I am > > really interested in the future plans for it. > > They needed some surgery to work on top of the node-LRU rewrite. I've > restored performance on the benchmarks I was using and will post them > after some more cleaning up and writing changelogs for the new pieces. > > > 2) swap trashing detection is something that we are lacking for a long > > time and it would be great if we could do something to help > > situations when the machine is effectively out of memory but still > > hopelessly trying to swap in and out few pages while the machine is > > basically unusable. I hope that 1) will give us some bases but I am > > not sure how much we will need on top. > > Yes, this keeps biting us quite frequently. Not with swap so much as > page cache, but it's the same problem: while we know all the thrashing > *events*, we don't know how much they truly cost us. I've started > drafting a thrashing quantification patch based on feedback from the > Kernel Summit, attaching it below. It's unbelievably crude and needs > more thought on sampling/decaying, as well as on filtering out swapins > that happen after pressure has otherwise subsided. But it does give me > a reasonable-looking thrashing ratio under memory pressure. > > > 3) optimizations for the swap out paths - Tim Chen and other guys from > > Intel are already working on this. I didn't get time to review this > > closely - mostly because I am not closely familiar with the swapout > > code and it takes quite some time to get into all subtle details. > > I mainly interested in what are the plans in this area and how they > > should be coordinated with other swap related changes > > 4) Do we want the native THP swap in/out support? > > Shaohua had some opinions on this, he might be interested in joining > this discussion. CCing him. Sure, I'm very interested in the topic. I'm pretty interested in reducing swap latency and making the latency more predictable. I had some random ideas and did some experiments before (no real patch though, sorry), like io poll for swapin, reduce reclaim batch count in direct page reclaim, and a flush-like proactive swapout and so on. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>