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vm: check for empty kstack cache before locking

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The current cache logic checks the total number of stacks in the kernel,
which even on small boxes significantly exceeds the 128 limit (e.g. an
8-way box with zfs has almost 800 stacks allocated).

Stacks are cached earlier for each main thread.

As a result the code is rarely executed, but when it is then (on boxes like
the above) it always fails. Since there are no provisions made for NUMA and
release time is approaching, just do a quick check to avoid acquiring the
lock.

Approved by:	re (kib)
This commit is contained in:
mjg 2018-09-19 16:02:33 +00:00
parent 4154c10832
commit e4a8d038e7
1 changed files with 1 additions and 1 deletions
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2
sys/vm/vm_glue.c
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@ -327,7 +327,7 @@ vm_thread_new(struct thread *td, int pages)
else if (pages > KSTACK_MAX_PAGES)
pages = KSTACK_MAX_PAGES;
if (pages == kstack_pages) {
if (pages == kstack_pages && kstack_cache != NULL) {
mtx_lock(&kstack_cache_mtx);
if (kstack_cache != NULL) {
ks_ce = kstack_cache;