Re: [PATCH 0/4] mm: zone lock tracepoint instrumentation

[Shakeel Butt]

On Fri, Feb 20, 2026 at 01:09:59PM -0600, Cheatham, Benjamin wrote:
> On 2/11/2026 9:22 AM, 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.
> > 
> > The goal is to enable detailed holder/waiter analysis and lock
> > hold time measurements without affecting the fast path when
> > tracing is disabled.
> > 
> > The series is structured as follows:
> > 
> >   1. Introduce zone lock wrappers.
> >   2. Mechanically convert zone lock users to the wrappers.
> >   3. Convert compaction to use the wrappers (requires minor
> >      restructuring of compact_lock_irqsave()).
> >   4. Add zone lock tracepoints.
> 
> I think you can improve the flow of this series if reorder as follows:
> 	1. Introduce zone lock wrappers
> 	4. Add zone lock tracepoints
> 	2. Mechanically convert zone lock users to the wrappers
> 	3. Convert compaction to use the wrappers...
> 
> and possibly squash 1 & 4 (though that might be too big of a patch). It's better to introduce the
> wrappers and their tracepoints together before the reviewer (i.e. me) forgets what was added in
> patch 1 by the time they get to patch 4.

I don't think this suggestion will make anything better. This just seems like a
different taste. If I make a suggestion, I would request to squash (1) and (2)
i.e. patch containing wrappers and their use together but that is just my taste
and would be a nit. The series ordering is good as is.