Wang, Wei W
2020-Feb-10 03:13 UTC
[PATCH RFC] virtio_balloon: conservative balloon page shrinking
On Saturday, February 8, 2020 8:33 PM, Tetsuo Handa wrote:> > Is this NUMA aware? Can "node-A's NR_FILE_PAGES is already 0 and > node-B's NR_FILE_PAGES is not 0, but allocation request which triggered this > shrinker wants to allocate from only node-B" happen?No, it's a global counter.>Can some thread keep > this shrinker defunctional by keep increasing NR_FILE_PAGES?Yes. Actually it's our intention - as long as there are pagecache pages, balloon pages are avoided to be reclaimed.> > Is this patch from "Re: Balloon pressuring page cache" thread? I hope that > the guest could start reclaiming memory based on host's request (like OOM > notifier chain) which is issued when host thinks that host is getting close to > OOM and thus guests should start returning their unused memory to host. > Maybe "periodically (e.g. 5 minutes)" in addition to "upon close to OOM > condition" is also possible.That's about the host usages. The host side management software decides when to issue a request to balloon (either periodically or event driven), I think there isn't anything we need to do in the balloon driver here. Best, Wei
Tetsuo Handa
2020-Feb-10 03:57 UTC
[PATCH RFC] virtio_balloon: conservative balloon page shrinking
Wang, Wei W wrote:> On Saturday, February 8, 2020 8:33 PM, Tetsuo Handa wrote: > > > > Is this NUMA aware? Can "node-A's NR_FILE_PAGES is already 0 and > > node-B's NR_FILE_PAGES is not 0, but allocation request which triggered this > > shrinker wants to allocate from only node-B" happen? > > No, it's a global counter. > > >Can some thread keep > > this shrinker defunctional by keep increasing NR_FILE_PAGES? > > Yes. Actually it's our intention - as long as there are pagecache pages, > balloon pages are avoided to be reclaimed.Then, "node-A's NR_FILE_PAGES is already 0 and node-B's NR_FILE_PAGES is not 0, but allocation request which triggered this shrinker wants to allocate from only node-A" would be confused by this change, for the pagecache pages for allocating thread's interested node are already depleted but the balloon cannot shrink when it should because the pagecache pages for allocating thread's uninterested nodes are not yet depleted.> > > > > > Is this patch from "Re: Balloon pressuring page cache" thread? I hope that > > the guest could start reclaiming memory based on host's request (like OOM > > notifier chain) which is issued when host thinks that host is getting close to > > OOM and thus guests should start returning their unused memory to host. > > Maybe "periodically (e.g. 5 minutes)" in addition to "upon close to OOM > > condition" is also possible. > > That's about the host usages. The host side management software decides when to > issue a request to balloon (either periodically or event driven), I think there > isn't anything we need to do in the balloon driver here.Well, my comment is rather: "Do not try to reserve guest's memory. In other words, do not try to maintain balloons on the guest side. Since host would be able to cache file data on the host's cache, guests would be able to quickly fetch file data from host's cache via normal I/O requests." ;-)
Wang, Wei W
2020-Feb-10 07:27 UTC
[PATCH RFC] virtio_balloon: conservative balloon page shrinking
On Monday, February 10, 2020 11:57 AM, Tetsuo Handa wrote:> Then, "node-A's NR_FILE_PAGES is already 0 and node-B's NR_FILE_PAGES is > not 0, but allocation request which triggered this shrinker wants to allocate > from only node-A" > would be confused by this change, for the pagecache pages for allocating > thread's interested node are already depleted but the balloon cannot shrink > when it should because the pagecache pages for allocating thread's > uninterested nodes are not yet depleted.The existing balloon isn't numa aware. "but the balloon cannot shrink " - even we let balloon to shrink, it could shrink pages from the uninterested node. When we have a numa aware balloon, we could further update the shrinker to check with the per node counter , node_page_state(NR_FILE_PAGES).> > > > Well, my comment is rather: "Do not try to reserve guest's memory. In other > words, do not try to maintain balloons on the guest side. Since host would > be able to cache file data on the host's cache, guests would be able to > quickly fetch file data from host's cache via normal I/O requests." ;-)Didn't this one. The discussion was about guest pagecache pages v.s. guest balloon pages. Why is host's pagecache here? Best, Wei
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