Re: [PATCH 04/24] shrinker: defer work only to kswapd

kbuild test robot
2019-08-07T16:13:55Z

Hi Dave,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to v5.3-rc3 next-20190807]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Dave-Chinner/mm-xfs-non-blocking-inode-reclaim/20190804-042311
reproduce:
# apt-get install sparse
# sparse version: v0.6.1-rc1-7-g2b96cd8-dirty
make ARCH=x86_64 allmodconfig
make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

sparse warnings: (new ones prefixed by >>)

>> mm/vmscan.c:539:70: sparse: sparse: incorrect type in argument 1 (different base types) @@ expected struct atomic64_t [usertype] *v @@ got ruct atomic64_t [usertype] *v @@
>> mm/vmscan.c:539:70: sparse: expected struct atomic64_t [usertype] *v
>> mm/vmscan.c:539:70: sparse: got struct atomic_t [usertype] *
arch/x86/include/asm/irqflags.h:54:9: sparse: sparse: context imbalance in 'check_move_unevictable_pages' - unexpected unlock

vim +539 mm/vmscan.c

498
499 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
500 struct shrinker *shrinker, int priority)
501 {
502 unsigned long freed = 0;
503 int64_t freeable_objects = 0;
504 int64_t scan_count;
505 int64_t scanned_objects = 0;
506 int64_t next_deferred = 0;
507 int64_t deferred_count = 0;
508 long new_nr;
509 int nid = shrinkctl->nid;
510 long batch_size = shrinker->batch ? shrinker->batch
511 : SHRINK_BATCH;
512
513 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
514 nid = 0;
515
516 scan_count = shrink_scan_count(shrinkctl, shrinker, priority,
517 &freeable_objects);
518 if (scan_count == 0 || scan_count == SHRINK_EMPTY)
519 return scan_count;
520
521 /*
522 * If kswapd, we take all the deferred work and do it here. We don't let
523 * direct reclaim do this, because then it means some poor sod is going
524 * to have to do somebody else's GFP_NOFS reclaim, and it hides the real
525 * amount of reclaim work from concurrent kswapd operations. Hence we do
526 * the work in the wrong place, at the wrong time, and it's largely
527 * unpredictable.
528 *
529 * By doing the deferred work only in kswapd, we can schedule the work
530 * according the the reclaim priority - low priority reclaim will do
531 * less deferred work, hence we'll do more of the deferred work the more
532 * desperate we become for free memory. This avoids the need for needing
533 * to specifically avoid deferred work windup as low amount os memory
534 * pressure won't excessive trim caches anymore.
535 */
536 if (current_is_kswapd()) {
537 int64_t deferred_scan;
538
> 539 deferred_count = atomic64_xchg(&shrinker->nr_deferred[nid], 0);
540
541 /* we want to scan 5-10% of the deferred work here at minimum */
542 deferred_scan = deferred_count;
543 if (priority)
544 do_div(deferred_scan, priority);
545 scan_count += deferred_scan;
546
547 /*
548 * If there is more deferred work than the number of freeable
549 * items in the cache, limit the amount of work we will carry
550 * over to the next kswapd run on this cache. This prevents
551 * deferred work windup.
552 */
553 if (deferred_count > freeable_objects * 2)
554 deferred_count = freeable_objects * 2;
555
556 }
557
558 /*
559 * Avoid risking looping forever due to too large nr value:
560 * never try to free more than twice the estimate number of
561 * freeable entries.
562 */
563 if (scan_count > freeable_objects * 2)
564 scan_count = freeable_objects * 2;
565
566 trace_mm_shrink_slab_start(shrinker, shrinkctl, deferred_count,
567 freeable_objects, scan_count,
568 scan_count, priority);
569
570 /*
571 * If the shrinker can't run (e.g. due to gfp_mask constraints), then
572 * defer the work to a context that can scan the cache.
573 */
574 if (shrinkctl->will_defer)
575 goto done;
576
577 /*
578 * Normally, we should not scan less than batch_size objects in one
579 * pass to avoid too frequent shrinker calls, but if the slab has less
580 * than batch_size objects in total and we are really tight on memory,
581 * we will try to reclaim all available objects, otherwise we can end
582 * up failing allocations although there are plenty of reclaimable
583 * objects spread over several slabs with usage less than the
584 * batch_size.
585 *
586 * We detect the "tight on memory" situations by looking at the total
587 * number of objects we want to scan (total_scan). If it is greater
588 * than the total number of objects on slab (freeable), we must be
589 * scanning at high prio and therefore should try to reclaim as much as
590 * possible.
591 */
592 while (scan_count >= batch_size ||
593 scan_count >= freeable_objects) {
594 unsigned long ret;
595 unsigned long nr_to_scan = min_t(long, batch_size, scan_count);
596
597 shrinkctl->nr_to_scan = nr_to_scan;
598 shrinkctl->nr_scanned = nr_to_scan;
599 ret = shrinker->scan_objects(shrinker, shrinkctl);
600 if (ret == SHRINK_STOP)
601 break;
602 freed += ret;
603
604 count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
605 scan_count -= shrinkctl->nr_scanned;
606 scanned_objects += shrinkctl->nr_scanned;
607
608 cond_resched();
609 }
610
611 done:
612 if (deferred_count)
613 next_deferred = deferred_count - scanned_objects;
614 else if (scan_count > 0)
615 next_deferred = scan_count;
616 /*
617 * move the unused scan count back into the shrinker in a
618 * manner that handles concurrent updates. If we exhausted the
619 * scan, there is no need to do an update.
620 */
621 if (next_deferred > 0)
622 new_nr = atomic_long_add_return(next_deferred,
623 &shrinker->nr_deferred[nid]);
624 else
625 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
626
627 trace_mm_shrink_slab_end(shrinker, nid, freed, deferred_count, new_nr,
628 scan_count);
629 return freed;
630 }
631

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