On 5/20/21 6:34 AM, Andrew Morton wrote:

On Wed, 19 May 2021 21:17:43 +0100 Aaron Tomlin [off-list ref] wrote:

quoted

It does not make sense to retry compaction when a fatal signal is
pending.

Well, it might make sense.  Presumably it is beneficial to other tasks.

Yeah but the compaction won't happen. compact_zone() will immediately detect it
via __compact_finished() and bail out. So in that sense it does not make sense
to retry :)

quoted

In the context of try_to_compact_pages(), indeed COMPACT_SKIPPED can be
returned; albeit, not every zone, on the zone list, would be considered
in the case a fatal signal is found to be pending.
Yet, in should_compact_retry(), given the last known compaction result,
each zone, on the zone list, can be considered/or checked
(see compaction_zonelist_suitable()). For example, if a zone was found
to succeed, then reclaim/compaction would be tried again
(notwithstanding the above).

This patch ensures that compaction is not needlessly retried
irrespective of the last known compaction result e.g. if it was skipped,
in the unlikely case a fatal signal is found pending.
So, OOM is at least attempted.

What observed problems motivated this change?

What were the observed runtime effects of this change?

Yep those details from the previous thread should be included here.