[PATCH 0/1] Hierarchical percpu counters preparation

[PATCH 0/1] Hierarchical percpu counters preparation

[Mathieu Desnoyers]

Hi Andrew,

This patch is a preparation step for HPCC, for the OOM killer
improvements. I suspect that this patch is useful on its own, because it
really makes no sense to sum up accounting statistics of use_mm within
kernel threads which are only temporarily using those mm.

Thanks,

Mathieu

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-mm@kvack.org

Mathieu Desnoyers (1):
  tsacct: Skip all kernel threads

 kernel/tsacct.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.39.5

[PATCH 1/1] tsacct: Skip all kernel threads

[Mathieu Desnoyers]

When we hit acct_account_cputime within a irq handler over a kthread
that happens to use a userspace mm, we end up summing up the mm's RSS
into the tsk acct_rss_mem1, which eventually decays.

I don't see a good rationale behind tracking the mm's rss in that way
when a kthread use a userspace mm temporarily through use_mm.

It causes issues with init_mm and efi_mm which only partially initialize
their mm_struct when introducing the new hierarchical percpu counters to
replace RSS counters, which requires a pointer dereference when reading
the approximate counter sum. The current percpu counters simply load a
zeroed atomic counter, which happen to work.

Skip all kernel threads in acct_account_cputime(), not just those that
happen to have a NULL mm.

This is a preparation step before introducing the hierarchical percpu
counters.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-mm@kvack.org
---
 kernel/tsacct.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 6ea2f6363b90..5c153106e642 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -125,7 +125,7 @@ static void __acct_update_integrals(struct task_struct *tsk,
 {
 	u64 time, delta;
 
-	if (!likely(tsk->mm))
+	if (unlikely(!tsk->mm || (tsk->flags & PF_KTHREAD)))
 		return;
 
 	time = stime + utime;
-- 
2.39.5