linux-kernel - Re: [PATCH 4/4] selftests: memcg: Remove protection from top level memcg

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Date:   Tue, 17 May 2022 17:24:43 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Michal Koutný <mkoutny@...e.com>,
        void@...ifault.com, cgroups@...r.kernel.org, hannes@...xchg.org,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...nel.org, shakeelb@...gle.com,
        tj@...nel.org, Richard Palethorpe <rpalethorpe@...e.de>
Subject: Re: [PATCH 4/4] selftests: memcg: Remove protection from top level
 memcg

On Fri, 13 May 2022 11:59:56 -0700 Roman Gushchin <roman.gushchin@...ux.dev> wrote:

> On Fri, May 13, 2022 at 07:18:11PM +0200, Michal Koutny wrote:
> > The reclaim is triggered by memory limit in a subtree, therefore the
> > testcase does not need configured protection against external reclaim.
> > 
> > Also, correct/deduplicate respective comments
> > 
> > Signed-off-by: Michal Koutný <mkoutny@...e.com>
> > ---
> >  tools/testing/selftests/cgroup/test_memcontrol.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> > index 9ffacf024bbd..9d370aafd799 100644
> > --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> > +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> > @@ -247,7 +247,7 @@ static int cg_test_proc_killed(const char *cgroup)
> >  
> >  /*
> >   * First, this test creates the following hierarchy:
> > - * A       memory.min = 50M,  memory.max = 200M
> > + * A       memory.min = 0,    memory.max = 200M
> >   * A/B     memory.min = 50M,  memory.current = 50M
> >   * A/B/C   memory.min = 75M,  memory.current = 50M
> >   * A/B/D   memory.min = 25M,  memory.current = 50M
> > @@ -257,7 +257,7 @@ static int cg_test_proc_killed(const char *cgroup)
> >   * Usages are pagecache, but the test keeps a running
> >   * process in every leaf cgroup.
> >   * Then it creates A/G and creates a significant
> > - * memory pressure in it.
> > + * memory pressure in A.
> >   *
> >   * A/B    memory.current ~= 50M
> >   * A/B/C  memory.current ~= 29M
> > @@ -335,8 +335,6 @@ static int test_memcg_min(const char *root)
> >  			      (void *)(long)fd);
> >  	}
> >  
> > -	if (cg_write(parent[0], "memory.min", "50M"))
> > -		goto cleanup;
> >  	if (cg_write(parent[1], "memory.min", "50M"))
> >  		goto cleanup;
> >  	if (cg_write(children[0], "memory.min", "75M"))
> > @@ -404,8 +402,8 @@ static int test_memcg_min(const char *root)
> >  
> >  /*
> >   * First, this test creates the following hierarchy:
> > - * A       memory.low = 50M,  memory.max = 200M
> > - * A/B     memory.low = 50M,  memory.current = 50M
> > + * A       memory.low = 0,    memory.max = 200M
> > + * A/B     memory.low = 50M,  memory.current = ...
> 
> Can you, please, just remove "memory.current = ...", it's not
> because obvious what "..." means here.
> 

You mean this?

--- a/tools/testing/selftests/cgroup/test_memcontrol.c~selftests-memcg-remove-protection-from-top-level-memcg-fix
+++ a/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -403,15 +403,14 @@ cleanup:
 /*
  * First, this test creates the following hierarchy:
  * A       memory.low = 0,    memory.max = 200M
- * A/B     memory.low = 50M,  memory.current = ...
+ * A/B     memory.low = 50M
  * A/B/C   memory.low = 75M,  memory.current = 50M
  * A/B/D   memory.low = 25M,  memory.current = 50M
  * A/B/E   memory.low = 0,    memory.current = 50M
  * A/B/F   memory.low = 500M, memory.current = 0
  *
  * Usages are pagecache.
- * Then it creates A/G an creates a significant
- * memory pressure in it.
+ * Then it creates A/G and creates significant memory pressure in it.
  *
  * Then it checks actual memory usages and expects that:
  * A/B    memory.current ~= 50M
_

(includes gratuitous comment cleanup)

I assume your comment in
https://lkml.kernel.org/r/Yn6pBPq+lAXm9NG8@carbon can be addressed in a
later patch.

I'm not sure what to amke of https://lkml.kernel.org/r/Yn6pWPodGPlz+D8G@carbon

Do we feel this series needs more work before merging it up?