On Mon, 6 Sep 2021 16:40:28 +0200 Vlastimil Babka wrote:

On 9/2/21 20:17, Mike Kravetz wrote:

quoted

Here is some very high level information from a long stall that was
interrupted.  This was an order 9 allocation from alloc_buddy_huge_page().

55269.530564] __alloc_pages_slowpath: jiffies 47329325 tries 609673 cpu_tries 1   node 0 FAIL
[55269.539893]     r_tries 25       c_tries 609647   reclaim 47325161 compact 607     

Yes, in __alloc_pages_slowpath for 47329325 jiffies before being interrupted.
should_reclaim_retry returned true 25 times and should_compact_retry returned
true 609647 times.
Almost all time (47325161 jiffies) spent in __alloc_pages_direct_reclaim, and
607 jiffies spent in __alloc_pages_direct_compact.

Looks like both
reclaim retries > MAX_RECLAIM_RETRIES
and
compaction retries > MAX_COMPACT_RETRIES

Yeah AFAICS that's only possible with the scenario I suspected. I guess
we should put a limit on compact retries (maybe some multiple of
MAX_COMPACT_RETRIES) even if it thinks that reclaim could help, while
clearly it doesn't (i.e. because somebody else is stealing the page like
in your test case).

And/or clamp reclaim retries for costly orders

	reclaim retries = MAX_RECLAIM_RETRIES - order;

to pull down the chance for stall as low as possible.