[Tarantool-patches] [small] Revert "Free all slabs on region reset"
Alexander Turenko
alexander.turenko at tarantool.org
Wed Jan 29 11:06:45 MSK 2020
This reverts commit 67d7ab44ab09df3356929e3692a03321b31f3ebb.
The goal of the reverted commit was to fix flaky fails of tarantool
tests that checks amount of memory used by a fiber:
| fiber.info()[fiber.self().id()].memory.used
It also attempts to overcome the situation when a fiber holds some
amount of memory, which is not used in any way. The high limit of such
memory is controlled by a threshold in fiber_gc() tarantool's function
(128 KiB at the moment):
| void
| fiber_gc(void)
| {
| if (region_used(&fiber()->gc) < 128 * 1024) {
| region_reset(&fiber()->gc);
| return;
| }
|
| region_free(&fiber()->gc);
| }
The reverted commit, however, leads to significant performance
degradation on certain workloads (see #4736). So the revertion fixes the
performance degradation and opens the problem with tests, which is
tracked in #4750.
Related to #12
Related to https://github.com/tarantool/tarantool/issues/4750
Fixes https://github.com/tarantool/tarantool/issues/4736
---
https://github.com/tarantool/small/tree/Totktonada/gh-4736-revert-region-reset
small/region.h | 18 ++++--------------
1 file changed, 4 insertions(+), 14 deletions(-)
diff --git a/small/region.h b/small/region.h
index d9be176..bea88c6 100644
--- a/small/region.h
+++ b/small/region.h
@@ -156,16 +156,6 @@ region_reserve(struct region *region, size_t size)
slab.next_in_list);
if (size <= rslab_unused(slab))
return (char *) rslab_data(slab) + slab->used;
- /* Try to get a slab from the region cache. */
- slab = rlist_last_entry(®ion->slabs.slabs,
- struct rslab,
- slab.next_in_list);
- if (slab->used == 0 && size <= rslab_unused(slab)) {
- /* Move this slab to the head. */
- slab_list_del(®ion->slabs, &slab->slab, next_in_list);
- slab_list_add(®ion->slabs, &slab->slab, next_in_list);
- return (char *) rslab_data(slab);
- }
}
return region_reserve_slow(region, size);
}
@@ -222,14 +212,14 @@ region_aligned_alloc(struct region *region, size_t size, size_t alignment)
/**
* Mark region as empty, but keep the blocks.
- * Do not change the first slab and use previous slabs as a cache to
- * use for future allocations.
*/
static inline void
region_reset(struct region *region)
{
- struct rslab *slab;
- rlist_foreach_entry(slab, ®ion->slabs.slabs, slab.next_in_list) {
+ if (! rlist_empty(®ion->slabs.slabs)) {
+ struct rslab *slab = rlist_first_entry(®ion->slabs.slabs,
+ struct rslab,
+ slab.next_in_list);
region->slabs.stats.used -= slab->used;
slab->used = 0;
}
--
2.22.0
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