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SubjectRe: [PATCH 2/2] vmscan: use atomic-long for shrinker batching
Konstantin Khlebnikov wrote:
> delta = (4 * nr_pages_scanned) / shrinker->seeks;
> @@ -329,12 +327,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
> * manner that handles concurrent updates. If we exhausted the
> * scan, there is no need to do an update.
> */
> - do {
> - nr = shrinker->nr;
> - new_nr = total_scan + nr;
> - if (total_scan<= 0)
> - break;
> - } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
> + if (total_scan> 0)
> + new_nr = atomic_long_add_return(total_scan,
> + &shrinker->nr_in_batch);
> + else
> + new_nr = atomic_long_read(&shrinker->nr_in_batch);
>
> trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);

BTW, new_nr required only for tracing, maybe this will be better/faster,
because atomic accuracy there isn't required at all.

if (total_scan > 0)
atomic_long_add(total_scan, &shrinker->nr_in_batch);

new_nr = atomic_long_read(&shrinker->nr_in_batch);
trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);


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