Re: [PATCH] vmscan: evict use-once pages first (v3)

Rik van Riel
2009-05-01T23:07:09Z

Andrew Morton wrote:
> On Wed, 29 Apr 2009 13:14:36 -0400
> Rik van Riel <riel@redhat.com> wrote:
>
>> When the file LRU lists are dominated by streaming IO pages,
>> evict those pages first, before considering evicting other
>> pages.
>>
>> This should be safe from deadlocks or performance problems
>> because only three things can happen to an inactive file page:
>> 1) referenced twice and promoted to the active list
>> 2) evicted by the pageout code
>> 3) under IO, after which it will get evicted or promoted
>>
>> The pages freed in this way can either be reused for streaming
>> IO, or allocated for something else. If the pages are used for
>> streaming IO, this pageout pattern continues. Otherwise, we will
>> fall back to the normal pageout pattern.
>>
>> ..
>>
>> +int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
>> +{
>> + unsigned long active;
>> + unsigned long inactive;
>> +
>> + inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
>> + active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
>> +
>> + return (active > inactive);
>> +}
>
> This function could trivially be made significantly more efficient by
> changing it to do a single pass over all the zones of all the nodes,
> rather than two passes.

How would I do that in a clean way?

The function mem_cgroup_inactive_anon_is_low and
the global versions all do the same. It would be
nice to make all four of them go fast :)

If there is no standardized infrastructure for
getting multiple statistics yet, I can probably
whip something up.

>> static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
>> struct zone *zone, struct scan_control *sc, int priority)
>> {
>> int file = is_file_lru(lru);
>>
>> - if (lru == LRU_ACTIVE_FILE) {
>> + if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
>> shrink_active_list(nr_to_scan, zone, sc, priority, file);
>> return 0;
>> }
>
> And it does get called rather often.

Same as inactive_anon_is_low.

Optimizing them might make sense if it turns out to
use a significant amount of CPU.

--
All rights reversed.