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Fix arena 0 deferral_allowed flag init

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Arena 0 have a dedicated initialization path, which differs from
initialization path of other arenas. The main difference for the purpose
of this change is that we initialize arena 0 before we initialize
background threads. HPA shard options have `deferral_allowed` flag which
should be equal to `background_thread_enabled()` return value, but it
wasn't the case before this change, because for arena 0
`background_thread_enabled()` was initialized correctly after arena 0
initialization phase already ended.

Below is initialization sequence for arena 0 after this commit to
illustrate everything still should be initialized correctly.

* `hpa_central_init` initializes HPA Central, before we initialize every
  HPA shard (including arena's 0).
* `background_thread_boot1` initializes `background_thread_enabled()`
  return value.
* `pa_shard_enable_hpa` initializes arena 0 HPA shard.

```
                       malloc_init_hard -------------
                      /           /                  \
                     /           /                    \
                    /           /                      \
malloc_init_hard_a0_locked  background_thread_boot1  pa_shard_enable_hpa
        /                     /                          \
       /                     /                            \
      /                     /                              \
arena_boot       background_thread_enabled_seta         hpa_shard_init
     |
     |
pa_central_init
     |
     |
hpa_central_init
```
This commit is contained in:
Dmitry Ilvokhin 2025-02-05 04:32:31 -08:00 • committed by Qi Wang
parent 421b17a622
commit 499f306859
3 changed files with 47 additions and 9 deletions
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4
src/arena.c
View file

@ -1789,8 +1789,8 @@ arena_new(tsdn_t *tsdn, unsigned ind, const arena_config_t *config) {
* We turn on the HPA if set to. There are two exceptions:
* - Custom extent hooks (we should only return memory allocated from
* them in that case).
* - Arena 0 initialization. In this case, we're mid-bootstrapping, and
* so arena_hpa_global is not yet initialized.
* - Arena 0 initialization. In this case, we're mid-bootstrapping,
* and so background_thread_enabled is not yet initialized.
*/
if (opt_hpa && ehooks_are_default(base_ehooks_get(base)) && ind != 0) {
hpa_shard_opts_t hpa_shard_opts = opt_hpa_opts;