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Message-Id: <20230823050609.2228718-3-mjguzik@gmail.com>
Date: Wed, 23 Aug 2023 07:06:09 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: linux-kernel@...r.kernel.org
Cc: dennis@...nel.org, tj@...nel.org, cl@...ux.com,
akpm@...ux-foundation.org, shakeelb@...gle.com,
vegard.nossum@...cle.com, linux-mm@...ck.org,
Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH v3 2/2] kernel/fork: group allocation/free of per-cpu counters for mm struct
A trivial execve scalability test which tries to be very friendly
(statically linked binaries, all separate) is predominantly bottlenecked
by back-to-back per-cpu counter allocations which serialize on global
locks.
Ease the pain by allocating and freeing them in one go.
Bench can be found here:
http://apollo.backplane.com/DFlyMisc/doexec.c
$ cc -static -O2 -o static-doexec doexec.c
$ ./static-doexec $(nproc)
Even at a very modest scale of 26 cores (ops/s):
before: 133543.63
after: 186061.81 (+39%)
While with the patch these allocations remain a significant problem,
the primary bottleneck shifts to page release handling.
Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
kernel/fork.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index d2e12b6d2b18..4f0ada33457e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -909,8 +909,6 @@ static void cleanup_lazy_tlbs(struct mm_struct *mm)
*/
void __mmdrop(struct mm_struct *mm)
{
- int i;
-
BUG_ON(mm == &init_mm);
WARN_ON_ONCE(mm == current->mm);
@@ -925,9 +923,8 @@ void __mmdrop(struct mm_struct *mm)
put_user_ns(mm->user_ns);
mm_pasid_drop(mm);
mm_destroy_cid(mm);
+ percpu_counter_destroy_many(mm->rss_stat, NR_MM_COUNTERS);
- for (i = 0; i < NR_MM_COUNTERS; i++)
- percpu_counter_destroy(&mm->rss_stat[i]);
free_mm(mm);
}
EXPORT_SYMBOL_GPL(__mmdrop);
@@ -1252,8 +1249,6 @@ static void mm_init_uprobes_state(struct mm_struct *mm)
static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
struct user_namespace *user_ns)
{
- int i;
-
mt_init_flags(&mm->mm_mt, MM_MT_FLAGS);
mt_set_external_lock(&mm->mm_mt, &mm->mmap_lock);
atomic_set(&mm->mm_users, 1);
@@ -1301,17 +1296,14 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
if (mm_alloc_cid(mm))
goto fail_cid;
- for (i = 0; i < NR_MM_COUNTERS; i++)
- if (percpu_counter_init(&mm->rss_stat[i], 0, GFP_KERNEL_ACCOUNT))
- goto fail_pcpu;
+ if (percpu_counter_init_many(mm->rss_stat, 0, GFP_KERNEL_ACCOUNT, NR_MM_COUNTERS))
+ goto fail_pcpu;
mm->user_ns = get_user_ns(user_ns);
lru_gen_init_mm(mm);
return mm;
fail_pcpu:
- while (i > 0)
- percpu_counter_destroy(&mm->rss_stat[--i]);
mm_destroy_cid(mm);
fail_cid:
destroy_context(mm);
--
2.41.0
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