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authorJosef Bacik <jbacik@fb.com>2018-01-31 16:16:26 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-01-31 17:18:36 -0800
commit9092c71bb724dba2ecba849eae69e5c9d39bd3d2 (patch)
tree7651f4c5ef17afb674b0982272a0eaf513765f1e /include
parentfcb2b0c577f145c7616843c9d4dcb4f9e5d88e29 (diff)
mm: use sc->priority for slab shrink targets
Previously we were using the ratio of the number of lru pages scanned to the number of eligible lru pages to determine the number of slab objects to scan. The problem with this is that these two things have nothing to do with each other, so in slab heavy work loads where there is little to no page cache we can end up with the pages scanned being a very low number. This means that we reclaim next to no slab pages and waste a lot of time reclaiming small amounts of space. Consider the following scenario, where we have the following values and the rest of the memory usage is in slab Active: 58840 kB Inactive: 46860 kB Every time we do a get_scan_count() we do this scan = size >> sc->priority where sc->priority starts at DEF_PRIORITY, which is 12. The first loop through reclaim would result in a scan target of 2 pages to 11715 total inactive pages, and 3 pages to 14710 total active pages. This is a really really small target for a system that is entirely slab pages. And this is super optimistic, this assumes we even get to scan these pages. We don't increment sc->nr_scanned unless we 1) isolate the page, which assumes it's not in use, and 2) can lock the page. Under pressure these numbers could probably go down, I'm sure there's some random pages from daemons that aren't actually in use, so the targets get even smaller. Instead use sc->priority in the same way we use it to determine scan amounts for the lru's. This generally equates to pages. Consider the following slab_pages = (nr_objects * object_size) / PAGE_SIZE What we would like to do is scan = slab_pages >> sc->priority but we don't know the number of slab pages each shrinker controls, only the objects. However say that theoretically we knew how many pages a shrinker controlled, we'd still have to convert this to objects, which would look like the following scan = shrinker_pages >> sc->priority scan_objects = (PAGE_SIZE / object_size) * scan or written another way scan_objects = (shrinker_pages >> sc->priority) * (PAGE_SIZE / object_size) which can thus be written scan_objects = ((shrinker_pages * PAGE_SIZE) / object_size) >> sc->priority which is just scan_objects = nr_objects >> sc->priority We don't need to know exactly how many pages each shrinker represents, it's objects are all the information we need. Making this change allows us to place an appropriate amount of pressure on the shrinker pools for their relative size. Link: http://lkml.kernel.org/r/1510780549-6812-1-git-send-email-josef@toxicpanda.com Signed-off-by: Josef Bacik <jbacik@fb.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Dave Chinner <david@fromorbit.com> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/trace/events/vmscan.h23
1 files changed, 10 insertions, 13 deletions
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index d70b53e65f43..e0b8b9173e1c 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -192,12 +192,12 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
TRACE_EVENT(mm_shrink_slab_start,
TP_PROTO(struct shrinker *shr, struct shrink_control *sc,
- long nr_objects_to_shrink, unsigned long pgs_scanned,
- unsigned long lru_pgs, unsigned long cache_items,
- unsigned long long delta, unsigned long total_scan),
+ long nr_objects_to_shrink, unsigned long cache_items,
+ unsigned long long delta, unsigned long total_scan,
+ int priority),
- TP_ARGS(shr, sc, nr_objects_to_shrink, pgs_scanned, lru_pgs,
- cache_items, delta, total_scan),
+ TP_ARGS(shr, sc, nr_objects_to_shrink, cache_items, delta, total_scan,
+ priority),
TP_STRUCT__entry(
__field(struct shrinker *, shr)
@@ -205,11 +205,10 @@ TRACE_EVENT(mm_shrink_slab_start,
__field(int, nid)
__field(long, nr_objects_to_shrink)
__field(gfp_t, gfp_flags)
- __field(unsigned long, pgs_scanned)
- __field(unsigned long, lru_pgs)
__field(unsigned long, cache_items)
__field(unsigned long long, delta)
__field(unsigned long, total_scan)
+ __field(int, priority)
),
TP_fast_assign(
@@ -218,24 +217,22 @@ TRACE_EVENT(mm_shrink_slab_start,
__entry->nid = sc->nid;
__entry->nr_objects_to_shrink = nr_objects_to_shrink;
__entry->gfp_flags = sc->gfp_mask;
- __entry->pgs_scanned = pgs_scanned;
- __entry->lru_pgs = lru_pgs;
__entry->cache_items = cache_items;
__entry->delta = delta;
__entry->total_scan = total_scan;
+ __entry->priority = priority;
),
- TP_printk("%pF %p: nid: %d objects to shrink %ld gfp_flags %s pgs_scanned %ld lru_pgs %ld cache items %ld delta %lld total_scan %ld",
+ TP_printk("%pF %p: nid: %d objects to shrink %ld gfp_flags %s cache items %ld delta %lld total_scan %ld priority %d",
__entry->shrink,
__entry->shr,
__entry->nid,
__entry->nr_objects_to_shrink,
show_gfp_flags(__entry->gfp_flags),
- __entry->pgs_scanned,
- __entry->lru_pgs,
__entry->cache_items,
__entry->delta,
- __entry->total_scan)
+ __entry->total_scan,
+ __entry->priority)
);
TRACE_EVENT(mm_shrink_slab_end,