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.
In addition, the bug in the replaced virtballoon_oom_notify that only
VIRTIO_BALLOON_ARRAY_PFNS_MAX (i.e 256) balloon pages can be freed
though the user has specified more than that number is fixed in the
shrinker_scan function.
Best,
Wei
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