linux-kernel - Re: [PATCH 2/6] tracing, page-allocator: Add trace events for anti-fragmentation falling back to other migratetypes

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Date:	Fri, 7 Aug 2009 13:02:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Larry Woodman <lwoodman@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/6] tracing, page-allocator: Add trace events for
	anti-fragmentation falling back to other migratetypes


* Mel Gorman <mel@....ul.ie> wrote:

> On Fri, Aug 07, 2009 at 10:02:49AM +0200, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mel@....ul.ie> wrote:
> > 
> > > +++ b/mm/page_alloc.c
> > > @@ -839,6 +839,12 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
> > >  							start_migratetype);
> > >  
> > >  			expand(zone, page, order, current_order, area, migratetype);
> > > +
> > > +			trace_mm_page_alloc_extfrag(page, order, current_order,
> > > +				start_migratetype, migratetype,
> > > +				current_order < pageblock_order,
> > > +				migratetype == start_migratetype);
> > 
> > This tracepoint too should be optimized some more:
> > 
> >  - pageblock_order can be passed down verbatim instead of the 
> >    'current_order < pageblock_order': it means one comparison less 
> >    in the fast-path, plus it gives more trace information as well.
> > 
> >  - migratetype == start_migratetype check is superfluous as both 
> >    values are already traced. This property can be added to the 
> >    TP_printk() post-processing stage instead, if the pretty-printing 
> >    is desired.
> > 
> 
> I think what you're saying that it's better to handle additional 
> information like this in TP_printk always. That's what I've 
> changed both of these into at least. I didn't even need to pass 
> down pageblock_order because it should be available in the 
> post-processing context from a header.

yeah. I formulated my suggestions in a trace-output-invariant way. 
If some information can be omitted altogether from the trace, the 
better.

> The additional parameters are not being passed down any more and 
> the TP_printk looks like
> 
>         TP_printk("page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d",
>                 __entry->page,
>                 page_to_pfn(__entry->page),
>                 __entry->alloc_order,
>                 __entry->fallback_order,
>                 pageblock_order,
>                 __entry->alloc_migratetype,
>                 __entry->fallback_migratetype,
>                 __entry->fallback_order < pageblock_order,
>                 __entry->alloc_migratetype == __entry->fallback_migratetype)
> 
> Is that what you meant?

yeah, this looks more compact.

A detail: we might still want to pass in pageblock_order somehow - 
for example 'perf' will get access to the raw binary record but wont 
run the above printk line.

	Ingo
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