On Sun, 3 Nov 2019 09:06:49 -0800 Matthew Wilcox wrote: > On Sun, Nov 03, 2019 at 07:57:27PM +0800, Hillf Danton wrote: > > The cpu preemption feature makes a task able to preempt other tasks > > of lower priorities for cpu. It has been around for a while. > > > > This work introduces task prio into page reclaiming in order to add > > the page preemption feature that makes a task able to preempt other > > tasks of lower priorities for page. > > > > No page will be reclaimed on behalf of tasks of lower priorities > > under pp, a two-edge feature that functions only under memory > > pressure, laying a barrier to pages flowing to lower prio, and the > > nice syscall is what users need to fiddle with it for instance if > > they have a bunch of workloads to run in datacenter, and some > > difficulty predicting the runtime working set size for every > > individual workload which is sensitive to jitters in lru pages. > > > > Currently pages are reclaimed without prio taken into account; pages > > can be reclaimed from tasks of lower priorities on behalf of > > higher-prio tasks and vice versa. > > > > s/and vice versa/only/ is what we need to make pp by definition, but > > it could not make a sense without prio introduced; otherwise we can > > simply skip deactivating the lru pages based on prio comprison, and > > work is done. > > > > The introduction consists of two parts. On the page side, we have to > > store the page owner task's prio in page, which needs an extra room the > > size of the int type in the page struct. That room sounds impossible > > without inflating the page struct size, and is walked around by making > > pp depend on CONFIG_64BIT. > > ... and !MEMCG. Which means that your work is uninteresting because all > the distros turn on CONFIG_MEMCG. I have no idea which one they turn on by default, ext4, btrfs or xfs, and why, but I think they feel free to do the right, or the left. So do users to configure and build the kernel they need to power their machines, a 4-socket server or a TV-top box. > You still haven't given us any numbers. Or a workload which actually > benefits from this patch. Though I do not know why it is turned on by distros and for what workloads, I would like to try to run a couple of the workloads you may have interest in. Thanks Hillf
