Re: [PATCH v2] mm: mmap_lock: optimize mmap_lock tracepoints

Axel Rasmussen
2024-11-27T20:10:20Z

No objections. :)

Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>

On Tue, Nov 26, 2024 at 11:29 AM Roman Gushchin
<roman.gushchin@linux.dev> wrote:
>
> On Mon, Nov 25, 2024 at 09:16:17AM -0800, Shakeel Butt wrote:
> > We are starting to deploy mmap_lock tracepoint monitoring across our
> > fleet and the early results showed that these tracepoints are consuming
> > significant amount of CPUs in kernfs_path_from_node when enabled.
> >
> > It seems like the kernel is trying to resolve the cgroup path in the
> > fast path of the locking code path when the tracepoints are enabled. In
> > addition for some application their metrics are regressing when
> > monitoring is enabled.
> >
> > The cgroup path resolution can be slow and should not be done in the
> > fast path. Most userspace tools, like bpftrace, provides functionality
> > to get the cgroup path from cgroup id, so let's just trace the cgroup
> > id and the users can use better tools to get the path in the slow path.
> >
> > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
>
> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
>
> Thanks!