* Stefan Strogin <s.strogin@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On 17/03/15 10:40, Ingo Molnar wrote:
> >
> > * Stefan Strogin <s.strogin@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> >>> +TRACE_EVENT(cma_alloc,
> >>> +
> >>> + TP_PROTO(struct cma *cma, struct page *page, int count),
> >>> +
> >>> + TP_ARGS(cma, page, count),
> >>> +
> >>> + TP_STRUCT__entry(
> >>> + __field(struct page *, page)
> >>> + __field(unsigned long, count)
> >>> + ),
> >>> +
> >>> + TP_fast_assign(
> >>> + __entry->page = page;
> >>> + __entry->count = count;
> >>> + ),
> >>> +
> >>> + TP_printk("page=%p pfn=%lu count=%lu",
> >>> + __entry->page,
> >>> + __entry->page ? page_to_pfn(__entry->page) : 0,
> >>> + __entry->count)
> >
> > So I'm wondering, the fast-assign side is not equivalent to the
> > TP_printk() side:
> >
> >>> + __entry->page = page;
> >>> + __entry->page ? page_to_pfn(__entry->page) : 0,
> >
> > to me it seems it would be useful if MM tracing standardized on pfn
> > printing. Just like you did for trace_cma_release().
> >
>
> Hello Ingo, thank you for the reply.
> I afraid there is no special sense in printing both struct page * and
> pfn. But cma_alloc() returns struct page *, cma_release receives struct
> page *, and pr_debugs in these functions print struct page *. Maybe it
> would be better to print the same here too?
So will the tracepoints primarily log 'struct page *'?
If yes, my question is: why not log pfn? pfn is much more informative
(it's a hardware property of the page, not a kernel-internal
descriptor like 'struct page *') , and it tells us (without knowing
the layout of the kernel) which NUMA node a given area lies on, etc.
Or do other mm tracepoints already (mistakenly) use 'struct page *'?
> > Again I'd double check the various boundary conditions.
> >
>
> Sorry, I don't quite understand. Boundary conditions are already
> [should be] checked in cma_alloc()/cma_release, we should only pass
> to a trace event the information we want to be known, isn't it so?
No, I mean tracing info boundary conditions: what is returned when no
such page is allocated, what is returned when pfn #0 is allocated,
etc.
Thanks,
Ingo
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