Re: mm: mkfs.ext4 invoked oom-killer on i386 - pagecache_get_page

[Naresh Kamboju]

On Thu, 11 Jun 2020 at 15:25, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>
> On Fri 29-05-20 11:49:20, Michal Hocko wrote:
> > On Fri 29-05-20 02:56:44, Chris Down wrote:
> > > Yafang Shao writes:
> > Agreed. Even if e{low,min} might still have some rough edges I am
> > completely puzzled how we could end up oom if none of the protection
> > path triggers which the additional debugging should confirm. Maybe my
> > debugging patch is incomplete or used incorrectly (maybe it would be
> > esier to use printk rather than trace_printk?).
>
> It would be really great if we could move forward. While the fix (which
> has been dropped from mmotm) is not super urgent I would really like to
> understand how it could hit the observed behavior. Can we double check
> that the debugging patch really doesn't trigger (e.g.
> s@trace_printk@printk in the first step)?

Please suggest to me the way to get more debug information
by providing kernel debug patches and extra kernel configs.

I have applied your debug patch and tested on top on linux next 20200612
but did not find any printk output while running mkfs -t ext4 /drive test case.


> I have checked it again but
> do not see any potential code path which would be affected by the patch
> yet not trigger any output. But another pair of eyes would be really
> great.


---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b6d84326bdf2..d13ce7b02de4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2375,6 +2375,8 @@ static void get_scan_count(struct lruvec
*lruvec, struct scan_control *sc,
  * sc->priority further than desirable.
  */
  scan = max(scan, SWAP_CLUSTER_MAX);
+
+ trace_printk("scan:%lu protection:%lu\n", scan, protection);
  } else {
  scan = lruvec_size;
  }
@@ -2618,6 +2620,7 @@ static void shrink_node_memcgs(pg_data_t *pgdat,
struct scan_control *sc)

  switch (mem_cgroup_protected(target_memcg, memcg)) {
  case MEMCG_PROT_MIN:
+ trace_printk("under min:%lu emin:%lu\n", memcg->memory.min,
memcg->memory.emin);
  /*
  * Hard protection.
  * If there is no reclaimable memory, OOM.
@@ -2630,6 +2633,7 @@ static void shrink_node_memcgs(pg_data_t *pgdat,
struct scan_control *sc)
  * there is an unprotected supply
  * of reclaimable memory from other cgroups.
  */
+ trace_printk("under low:%lu elow:%lu\n", memcg->memory.low,
memcg->memory.elow);
  if (!sc->memcg_low_reclaim) {
  sc->memcg_low_skipped = 1;
  continue;
-- 
2.23.0

ref:
test output:
https://lkft.validation.linaro.org/scheduler/job/1489767#L1388

Test artifacts link (kernel / modules):
https://builds.tuxbuild.com/5rRNgQqF_wHsSRptdj4A1A/
- Naresh