Re: [PATCH v2 7/7] mm/tracing: introduce max_vma_count_exceeded trace event

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

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@linux-foundation.org>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
> > Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > Cc: Mike Rapoport <rppt@kernel.org>
> > Cc: Minchan Kim <minchan@kernel.org>
> > Cc: Pedro Falcato <pfalcato@suse.de>
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.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@oracle.com>
Date: Thu, 18 Sep 2025 14:47:10 +0100
Subject: [PATCH] fix

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.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 */
--
2.51.0