On Wed 01-08-18 19:12:25, Wei Wang wrote: > On 07/30/2018 05:00 PM, Michal Hocko wrote: > > On Fri 27-07-18 17:24:55, Wei Wang wrote: > > > The OOM notifier is getting deprecated to use for the reasons mentioned > > > here by Michal Hocko: https://lkml.org/lkml/2018/7/12/314 > > > > > > This patch replaces the virtio-balloon oom notifier with a shrinker > > > to release balloon pages on memory pressure. > > It would be great to document the replacement. This is not a small > > change... > > OK. I plan to document the following to the commit log: > > The OOM notifier is getting deprecated to use for the reasons: > - As a callout from the oom context, it is too subtle and easy to > generate bugs and corner cases which are hard to track; > - It is called too late (after the reclaiming has been performed). > Drivers with large amuont of reclaimable memory is expected to be > released them at an early age of memory pressure; > - The notifier callback isn't aware of the oom contrains; > Link: https://lkml.org/lkml/2018/7/12/314 > > This patch replaces the virtio-balloon oom notifier with a shrinker > to release balloon pages on memory pressure. Users can set the amount of > memory pages to release each time a shrinker_scan is called via the > module parameter balloon_pages_to_shrink, and the default amount is 256 > pages. Historically, the feature VIRTIO_BALLOON_F_DEFLATE_ON_OOM has > been used to release balloon pages on OOM. We continue to use this > feature bit for the shrinker, so the shrinker is only registered when > this feature bit has been negotiated with host. Do you have any numbers for how does this work in practice? Let's say you have a medium page cache workload which triggers kswapd to do a light reclaim? Hardcoded shrinking sounds quite dubious to me but I have no idea how people expect this to work. Shouldn't this be more adaptive? How precious are those pages anyway? -- Michal Hocko SUSE Labs
