Re: [PATCH v4 0/5] mm: zone lock tracepoint instrumentation

[Matthew Wilcox <willy@infradead.org>]

On Fri, Feb 27, 2026 at 04:00:22PM +0000, Dmitry Ilvokhin wrote:
> Zone lock contention can significantly impact allocation and
> reclaim latency, as it is a central synchronization point in
> the page allocator and reclaim paths. Improved visibility into
> its behavior is therefore important for diagnosing performance
> issues in memory-intensive workloads.
> 
> On some production workloads at Meta, we have observed noticeable
> zone lock contention. Deeper analysis of lock holders and waiters
> is currently difficult with existing instrumentation.
> 
> While generic lock contention_begin/contention_end tracepoints
> cover the slow path, they do not provide sufficient visibility
> into lock hold times. In particular, the lack of a release-side
> event makes it difficult to identify long lock holders and
> correlate them with waiters. As a result, distinguishing between
> short bursts of contention and pathological long hold times
> requires additional instrumentation.
> 
> This patch series adds dedicated tracepoint instrumentation to
> zone lock, following the existing mmap_lock tracing model.

I don't like this at all.  We have CONFIG_LOCK_STAT.  That should be
improved insted of coming up with one-offs for every single lock
that someone deems "special".