Re: [PATCH v7 1/6] mm/rmap: add tracepoint for rmap_walk

[David Hildenbrand (Arm)]

On 5/30/26 11:03, xu.xin16@xxxxxxxxxx wrote:
> From: xu xin <xu.xin16@xxxxxxxxxx>
> 
> Add trace_rmap_walk_start() and trace_rmap_walk_end() to bracket
> reverse mapping walks.  Unlike manual clock sampling, these
> tracepoints record no timestamp; latency can be computed offline
> by tools (e.g., perf, trace-cmd) using the event timestamps.
> 
> When tracepoints are disabled, the only cost is a static branch
> check (no clock read, no duration calculation), making them
> suitable for production use.
> 
> The information (folio type, locked state) helps diagnose
> performance issues in KSM, anonymous, and file-backed rmap walks.
> 
> Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
> ---

Learning that trace events can easily become stable ABI, we should consider
dropping this patch or switching to DECLARE_TRACE().

See Steve's explanation:

https://lore.kernel.org/r/20260603130006.7d2c4a62@xxxxxxxxxxxxxxxxxx

I assume this could be carried as an OOT patch when really working debugging
scenarios?

-- 
Cheers,

David