On 06/01/2016 03:51 PM, Michal Hocko wrote:
On Tue 31-05-16 15:08:12, Vlastimil Babka wrote:
During reclaim/compaction loop, compaction priority can be increased by the
should_compact_retry() function, but the current code is not optimal. Priority
is only increased when compaction_failed() is true, which means that compaction
has scanned the whole zone. This may not happen even after multiple attempts
with the lower priority due to parallel activity, so we might needlessly
struggle on the lower priority.
We can remove these corner cases by increasing compaction priority regardless
of compaction_failed(). Examining further the compaction result can be
postponed only after reaching the highest priority. This is a simple solution
and we don't need to worry about reaching the highest priority "too soon" here,
because hen should_compact_retry() is called it means that the system is
already struggling and the allocation is supposed to either try as hard as
possible, or it cannot fail at all. There's not much point staying at lower
priorities with heuristics that may result in only partial compaction.
The only exception here is the COMPACT_SKIPPED result, which means that
compaction could not run at all due to being below order-0 watermarks. In that
case, don't increase compaction priority, and check if compaction could proceed
when everything reclaimable was reclaimed. Before this patch, this was tied to
compaction_withdrawn(), but the other results considered there are in fact only
possible due to low compaction priority so we can ignore them thanks to the
patch. Since there are no other callers of compaction_withdrawn(), remove it.
I agree with the change in general. I think that keeping compaction_withdrawn
even with a single check is better because it abstracts the fact from a
specific constant.
OK.
Now that I think about that some more I guess you also want to update
compaction_retries inside should_compact_retry as well, or at least
update it only when we have reached the lowest priority. What do you
think?
Makes sense, especially that after your suggestion,
should_compact_retry() is not reached as long as should_reclaim_retry()
returnes true. So I will do that.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Other than that this makes sense
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
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