From: Johannes Weiner <hannes@cmpxchg.org>
To: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 5/7] memcg: pr_warn_once for unexpected events and stats
Date: Sat, 27 Apr 2024 10:22:34 -0400 [thread overview]
Message-ID: <20240427142234.GA1155473@cmpxchg.org> (raw)
In-Reply-To: <dsxeqlmrxyxfi2i7yzhdrukwiczh7sjcwfobaytdgkckjez36b@u6ooikkgyyf4>
On Fri, Apr 26, 2024 at 06:18:13PM -0700, Shakeel Butt wrote:
> On Fri, Apr 26, 2024 at 05:58:16PM -0700, Yosry Ahmed wrote:
> > On Fri, Apr 26, 2024 at 5:38 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> > >
> > > To reduce memory usage by the memcg events and stats, the kernel uses
> > > indirection table and only allocate stats and events which are being
> > > used by the memcg code. To make this more robust, let's add warnings
> > > where unexpected stats and events indexes are used.
> > >
> > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
> > > ---
> > > mm/memcontrol.c | 43 ++++++++++++++++++++++++++++++++++---------
> > > 1 file changed, 34 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 103e0e53e20a..36145089dcf5 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -671,9 +671,11 @@ unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
> > > return node_page_state(lruvec_pgdat(lruvec), idx);
> > >
> > > i = memcg_stats_index(idx);
> > > - if (i >= 0) {
> > > + if (likely(i >= 0)) {
> > > pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> > > x = READ_ONCE(pn->lruvec_stats->state[i]);
> > > + } else {
> > > + pr_warn_once("%s: stat item index: %d\n", __func__, idx);
> > > }
> >
> > Can we make these more compact by using WARN_ON_ONCE() instead:
> >
> > if (WARN_ON_ONCE(i < 0))
> > return 0;
> >
> > I guess the advantage of using pr_warn_once() is that we get to print
> > the exact stat index, but the stack trace from WARN_ON_ONCE() should
> > make it obvious in most cases AFAICT.
if (WARN_ONCE(i < 0, "stat item %d not in memcg_node_stat_items\n", i))
return 0;
should work?
> > No strong opinions either way.
>
> One reason I used pr_warn_once() over WARN_ON_ONCE() is the syzbot
> trigger. No need to trip the bot over this error condition.
The warn splat is definitely quite verbose. But I think that would
only be annoying initially, in case a site was missed. Down the line,
it seems helpful to have this stand out to somebody who is trying to
add a new cgroup stat and forgets to update the right enums.
next prev parent reply other threads:[~2024-04-27 14:22 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-27 0:37 [PATCH v2 0/7] memcg: reduce memory consumption by memcg stats Shakeel Butt
2024-04-27 0:37 ` [PATCH v2 1/7] memcg: reduce memory size of mem_cgroup_events_index Shakeel Butt
2024-04-27 0:42 ` Yosry Ahmed
2024-04-27 1:15 ` Shakeel Butt
2024-04-29 15:36 ` Roman Gushchin
2024-04-27 0:37 ` [PATCH v2 2/7] memcg: dynamically allocate lruvec_stats Shakeel Butt
2024-04-27 1:23 ` Yosry Ahmed
2024-04-29 15:50 ` Roman Gushchin
2024-04-29 19:46 ` Shakeel Butt
2024-04-29 21:02 ` Roman Gushchin
2024-04-29 21:59 ` Shakeel Butt
2024-04-27 0:37 ` [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats Shakeel Butt
2024-04-27 0:51 ` Yosry Ahmed
2024-04-27 1:16 ` Shakeel Butt
2024-04-27 1:18 ` Yosry Ahmed
2024-04-29 16:00 ` Roman Gushchin
2024-04-29 20:00 ` Shakeel Butt
2024-04-29 17:35 ` T.J. Mercier
2024-04-29 20:13 ` Shakeel Butt
2024-04-29 22:23 ` T.J. Mercier
2024-04-27 0:37 ` [PATCH v2 4/7] memcg: cleanup __mod_memcg_lruvec_state Shakeel Butt
2024-04-27 0:53 ` Yosry Ahmed
2024-04-29 15:45 ` Roman Gushchin
2024-04-27 0:37 ` [PATCH v2 5/7] memcg: pr_warn_once for unexpected events and stats Shakeel Butt
2024-04-27 0:58 ` Yosry Ahmed
2024-04-27 1:18 ` Shakeel Butt
2024-04-27 14:22 ` Johannes Weiner [this message]
2024-04-29 19:54 ` Shakeel Butt
2024-04-29 16:06 ` Roman Gushchin
2024-04-29 19:56 ` Shakeel Butt
2024-04-27 0:37 ` [PATCH v2 6/7] memcg: use proper type for mod_memcg_state Shakeel Butt
2024-04-27 0:37 ` [PATCH v2 7/7] mm: cleanup WORKINGSET_NODES in workingset Shakeel Butt
2024-04-29 16:07 ` Roman Gushchin
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