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

Roman Gushchin
2024-11-26T19:29:22Z

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!