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Allow opt.tcache_max to accept small size classes.

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Previously all the small size classes were cached.  However this has downsides
-- particularly when page size is greater than 4K (e.g. iOS), which will result
in much higher SMALL_MAXCLASS.

This change allows tcache_max to be set to lower values, to better control
resources taken by tcache.
This commit is contained in:
Qi Wang
2020-10-21 19:47:57 -07:00
committed by Qi Wang
parent ea32060f9c
commit bf72188f80
10 changed files with 265 additions and 33 deletions
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52
src/tcache.c
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@@ -62,7 +62,9 @@ cache_bin_info_t *tcache_bin_info;
static size_t tcache_bin_alloc_size;
static size_t tcache_bin_alloc_alignment;
/* Number of cache bins enabled, including both large and small. */
unsigned nhbins;
/* Max size class to be cached (can be small or large). */
size_t tcache_maxclass;
tcaches_t *tcaches;
@@ -567,7 +569,14 @@ tcache_init(tsd_t *tsd, tcache_slow_t *tcache_slow, tcache_t *tcache,
tcache_slow->arena = NULL;
tcache_slow->dyn_alloc = mem;
memset(tcache->bins, 0, sizeof(cache_bin_t) * nhbins);
/*
* We reserve cache bins for all small size classes, even if some may
* not get used (i.e. bins higher than nhbins). This allows the fast
* and common paths to access cache bin metadata safely w/o worrying
* about which ones are disabled.
*/
unsigned n_reserved_bins = nhbins < SC_NBINS ? SC_NBINS : nhbins;
memset(tcache->bins, 0, sizeof(cache_bin_t) * n_reserved_bins);
size_t cur_offset = 0;
cache_bin_preincrement(tcache_bin_info, nhbins, mem,
@@ -576,19 +585,34 @@ tcache_init(tsd_t *tsd, tcache_slow_t *tcache_slow, tcache_t *tcache,
if (i < SC_NBINS) {
tcache_slow->lg_fill_div[i] = 1;
tcache_slow->bin_refilled[i] = false;
tcache_slow->bin_flush_delay_items[i]
= tcache_gc_item_delay_compute(i);
}
cache_bin_t *cache_bin = &tcache->bins[i];
cache_bin_init(cache_bin, &tcache_bin_info[i], mem,
&cur_offset);
}
/*
* For small size classes beyond tcache_maxclass (i.e. nhbins < NBINS),
* their cache bins are initialized to a state to safely and efficiently
* fail all fastpath alloc / free, so that no additional check around
* nhbins is needed on fastpath.
*/
for (unsigned i = nhbins; i < SC_NBINS; i++) {
/* Disabled small bins. */
cache_bin_t *cache_bin = &tcache->bins[i];
void *fake_stack = mem;
size_t fake_offset = 0;
cache_bin_init(cache_bin, &tcache_bin_info[i], fake_stack,
&fake_offset);
assert(tcache_small_bin_disabled(i, cache_bin));
}
cache_bin_postincrement(tcache_bin_info, nhbins, mem,
&cur_offset);
/* Sanity check that the whole stack is used. */
assert(cur_offset == tcache_bin_alloc_size);
for (unsigned i = 0; i < SC_NBINS; i++) {
tcache_slow->bin_flush_delay_items[i]
= tcache_gc_item_delay_compute(i);
}
}
/* Initialize auto tcache (embedded in TSD). */
@@ -935,9 +959,6 @@ tcache_ncached_max_compute(szind_t szind) {
bool
tcache_boot(tsdn_t *tsdn, base_t *base) {
tcache_maxclass = sz_s2u(opt_tcache_max);
if (tcache_maxclass < SC_SMALL_MAXCLASS) {
tcache_maxclass = SC_SMALL_MAXCLASS;
}
assert(tcache_maxclass <= TCACHE_MAXCLASS_LIMIT);
nhbins = sz_size2index(tcache_maxclass) + 1;
@@ -946,16 +967,25 @@ tcache_boot(tsdn_t *tsdn, base_t *base) {
return true;
}
/* Initialize tcache_bin_info. */
tcache_bin_info = (cache_bin_info_t *)base_alloc(tsdn, base,
nhbins * sizeof(cache_bin_info_t), CACHELINE);
/* Initialize tcache_bin_info. See comments in tcache_init(). */
unsigned n_reserved_bins = nhbins < SC_NBINS ? SC_NBINS : nhbins;
size_t size = n_reserved_bins * sizeof(cache_bin_info_t);
tcache_bin_info = (cache_bin_info_t *)base_alloc(tsdn, base, size,
CACHELINE);
if (tcache_bin_info == NULL) {
return true;
}
for (szind_t i = 0; i < nhbins; i++) {
unsigned ncached_max = tcache_ncached_max_compute(i);
cache_bin_info_init(&tcache_bin_info[i], ncached_max);
}
for (szind_t i = nhbins; i < SC_NBINS; i++) {
/* Disabled small bins. */
cache_bin_info_init(&tcache_bin_info[i], 0);
assert(tcache_small_bin_disabled(i, NULL));
}
cache_bin_info_compute_alloc(tcache_bin_info, nhbins,
&tcache_bin_alloc_size, &tcache_bin_alloc_alignment);