linux-kernel - Re: [PATCH v2 7/7] mm/tracing: introduce max_vma_count

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Message-ID: <CAC_TJvdRf3xJg7FgTzAxa-ZrHkGA0G3dEDVWWWttg3ri2B-FNw@mail.gmail.com>
Date: Thu, 18 Sep 2025 08:55:10 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: akpm@...ux-foundation.org, minchan@...nel.org, david@...hat.com, 
	Liam.Howlett@...cle.com, rppt@...nel.org, pfalcato@...e.de, 
	kernel-team@...roid.com, android-mm@...gle.com, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Kees Cook <kees@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>, 
	Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, Jann Horn <jannh@...gle.com>, 
	Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 7/7] mm/tracing: introduce max_vma_count_exceeded trace event

On Thu, Sep 18, 2025 at 6:52 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
>
> On Thu, Sep 18, 2025 at 02:42:16PM +0100, Lorenzo Stoakes wrote:
> > On Mon, Sep 15, 2025 at 09:36:38AM -0700, Kalesh Singh wrote:
> > > Needed observability on in field devices can be collected with minimal
> > > overhead and can be toggled on and off. Event driven telemetry can be
> > > done with tracepoint BPF programs.
> > >
> > > The process comm is provided for aggregation across devices and tgid is
> > > to enable per-process aggregation per device.
> > >
> > > This allows for observing the distribution of such problems in the
> > > field, to deduce if there are legitimate bugs or if a bump to the limit is
> > > warranted.
> >
> > It's not really a bug though is it? It's somebody running out of resources.
> >
> > I'm not sure how useful this is really. But I'm open to being convinced!
> >
> > I also wonder if this is better as a statistic? You'd figure out it was a
> > problem that way too right?
> >
> > >
> > > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > > Cc: David Hildenbrand <david@...hat.com>
> > > Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > > Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > > Cc: Mike Rapoport <rppt@...nel.org>
> > > Cc: Minchan Kim <minchan@...nel.org>
> > > Cc: Pedro Falcato <pfalcato@...e.de>
> > > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> >
> > This breaks the VMA tests, please make sure to always check them:
> >
> > cc -I../shared -I. -I../../include -I../../arch/x86/include -I../../../lib -g -Og -Wall -D_LGPL_SOURCE -fsanitize=address -fsanitize=undefined    -c -o vma.o vma.c
> > In file included from vma.c:33:
> > ../../../mm/vma.c:10:10: fatal error: trace/events/vma.h: No such file or directory
> >    10 | #include <trace/events/vma.h>
> >       |          ^~~~~~~~~~~~~~~~~~~~
> > compilation terminated.
> > make: *** [<builtin>: vma.o] Error 1
>
> Trivial build fix:
>
> ----8<----
> From fe4c30abbd302ccc628ec92381ac10cea31c6d85 Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date: Thu, 18 Sep 2025 14:47:10 +0100
> Subject: [PATCH] fix
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  mm/vma.c                         | 2 --
>  mm/vma_internal.h                | 2 ++
>  tools/testing/vma/vma_internal.h | 4 ++++
>  3 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vma.c b/mm/vma.c
> index 26046b28cdda..a11d29a2ddc0 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -7,8 +7,6 @@
>  #include "vma_internal.h"
>  #include "vma.h"
>
> -#include <trace/events/vma.h>
> -
>  struct mmap_state {
>         struct mm_struct *mm;
>         struct vma_iterator *vmi;
> diff --git a/mm/vma_internal.h b/mm/vma_internal.h
> index 2f05735ff190..2f5ba679f43d 100644
> --- a/mm/vma_internal.h
> +++ b/mm/vma_internal.h
> @@ -47,6 +47,8 @@
>  #include <linux/uprobes.h>
>  #include <linux/userfaultfd_k.h>
>
> +#include <trace/events/vma.h>
> +
>  #include <asm/current.h>
>  #include <asm/tlb.h>
>
> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 07f4108c5e4c..c08c91861b9a 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -1661,4 +1661,8 @@ static inline void vma_count_dec(struct mm_struct *mm)
>         vma_count_sub(mm, 1);
>  }
>
> +static void trace_max_vma_count_exceeded(struct task_struct *task)
> +{
> +}
> +
>  #endif /* __MM_VMA_INTERNAL_H */

I made a point to build and run your tests, seems I forgot to actually
test it with this last patch.

Thanks for the fix.

--Kalesh

> --
> 2.51.0