Re: [PATCH] mm: Reward slab shrinkers that reclaim more than they were asked
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2017-08-15 22:30:15
Also in:
intel-gfx
On Sat, 12 Aug 2017 12:34:37 +0100 Chris Wilson [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Some shrinkers may only be able to free a bunch of objects at a time, and so free more than the requested nr_to_scan in one pass. Account for the extra freed objects against the total number of objects we intend to free, otherwise we may end up penalising the slab far more than intended. ...--- a/mm/vmscan.c +++ b/mm/vmscan.c@@ -398,6 +398,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, break; freed += ret; + nr_to_scan = max(nr_to_scan, ret); count_vm_events(SLABS_SCANNED, nr_to_scan); total_scan -= nr_to_scan; scanned += nr_to_scan;
Well... kinda. But what happens if the shrinker scanned more objects than requested but failed to free many of them? Of if the shrinker scanned less than requested? We really want to return nr_scanned from the shrinker invocation. Could we add a field to shrink_control for this?
--- a/mm/vmscan.c~a
+++ a/mm/vmscan.c@@ -393,14 +393,15 @@ static unsigned long do_shrink_slab(stru unsigned long nr_to_scan = min(batch_size, total_scan); shrinkctl->nr_to_scan = nr_to_scan; + shrinkctl->nr_scanned = nr_to_scan; ret = shrinker->scan_objects(shrinker, shrinkctl); if (ret == SHRINK_STOP) break; freed += ret; - count_vm_events(SLABS_SCANNED, nr_to_scan); - total_scan -= nr_to_scan; - scanned += nr_to_scan; + count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned); + total_scan -= shrinkctl->nr_scanned; + scanned += shrinkctl->nr_scanned; cond_resched(); }
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