On Fri, Mar 11, 2016 at 11:34:40AM +0300, Vladimir Davydov wrote: > On Thu, Mar 10, 2016 at 03:50:13PM -0500, Johannes Weiner wrote: > > When setting memory.high below usage, nothing happens until the next > > charge comes along, and then it will only reclaim its own charge and > > not the now potentially huge excess of the new memory.high. This can > > cause groups to stay in excess of their memory.high indefinitely. > > > > To fix that, when shrinking memory.high, kick off a reclaim cycle that > > goes after the delta. > > I agree that we should reclaim the high excess, but I don't think it's a > good idea to do it synchronously. Currently, memory.low and memory.high > knobs can be easily used by a single-threaded load manager implemented > in userspace, because it doesn't need to care about potential stalls > caused by writes to these files. After this change it might happen that > a write to memory.high would take long, seconds perhaps, so in order to > react quickly to changes in other cgroups, a load manager would have to > spawn a thread per each write to memory.high, which would complicate its > implementation significantly. While I do expect memory.high to be adjusted every once in a while, I can't see anybody doing it by a significant fraction of the cgroup every couple of seconds - or tighter than the workingset; and dropping use-once cache is cheap. What kind of usecase would that be? But even if we're wrong about it and this becomes a scalability issue, the knob - even when reclaiming synchroneously - makes no guarantees about the target being met once the write finishes. It's a best effort mechanism. What would break if we made it async later on? -- 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>