romenskiy2012/jemalloc
1
0
Fork 0
mirror of https://github.com/jemalloc/jemalloc.git synced 2026-07-08 23:07:20 +03:00
Code Issues Projects Releases Packages Wiki Activity

Add more documentation to decay.c

Browse source 
It took me a while to understand why some things are implemented the way they
are, so hopefully it will help future readers.
This commit is contained in:
Alex Lapenkou 2021-07-20 13:22:05 -07:00 • committed by Qi Wang
parent 4b633b9a81
commit aaea4fd1e6
2 changed files with 23 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

21
src/decay.c
View file

@ -102,6 +102,11 @@ decay_backlog_npages_limit(const decay_t *decay) {
return npages_limit_backlog;
}
/*
* Update backlog, assuming that 'nadvance_u64' time intervals have passed.
* Trailing 'nadvance_u64' records should be erased and 'current_npages' is
* placed as the newest record.
*/
static void
decay_backlog_update(decay_t *decay, uint64_t nadvance_u64,
size_t current_npages) {
@ -176,6 +181,22 @@ decay_maybe_advance_epoch(decay_t *decay, nstime_t *new_time,
return true;
}
/*
* Calculate how many pages should be purged after 'interval'.
*
* First, calculate how many pages should remain at the moment, then subtract
* the number of pages that should remain after 'interval'. The difference is
* how many pages should be purged until then.
*
* The number of pages that should remain at a specific moment is calculated
* like this: pages(now) = sum(backlog[i] * h_steps[i]). After 'interval'
* passes, backlog would shift 'interval' positions to the left and sigmoid
* curve would be applied starting with backlog[interval].
*
* The implementation doesn't directly map to the description, but it's
* essentially the same calculation, optimized to avoid iterating over
* [interval..SMOOTHSTEP_NSTEPS) twice.
*/
static inline size_t
decay_npurge_after_interval(decay_t *decay, size_t interval) {
size_t i;