Re: [PATCH 1/3] Add a new field to struct shrinker

On Fri, Jul 29, 2016 at 10:13:40AM +1000, Dave Chinner wrote:

On Thu, Jul 28, 2016 at 11:25:13AM +0100, Mel Gorman wrote:

quoted

On Thu, Jul 28, 2016 at 03:49:47PM +1000, Dave Chinner wrote:

quoted

Seems you're all missing the obvious.

Add a tracepoint for a shrinker callback that includes a "name"
field, have the shrinker callback fill it out appropriately. e.g
in the superblock shrinker:

	trace_shrinker_callback(shrinker, shrink_control, sb->s_type->name);

That misses capturing the latency of the call unless there is a begin/end
tracepoint.

Sure, but I didn't see that in the email talking about how to add a
name. Even if it is a requirement, it's not necessary as we've
already got shrinker runtime measurements from the
trace_mm_shrink_slab_start and trace_mm_shrink_slab_end trace
points. With the above callback event, shrinker call runtime is
simply the time between the calls to the same shrinker within
mm_shrink_slab start/end trace points.

Fair point. It's not that hard to correlate them.

<SNIP>

quoted

My understanding was the point of the tracepoints was to get detailed
information on points where the kernel is known to stall for long periods
of time.

First I've heard that's what tracepoints are supposed to be used
for.

I meant the specific case of trace_X_begin followed by trace_X_end, not
tracepoints in general.

-- 
Mel Gorman
SUSE Labs

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