Re: [PATCH 1/4] tracing, page-allocator: Add trace events for page allocation and page freeing

KOSAKI Motohiro
2009-08-05T09:13:13Z

Hi

sorry for the delayed review.

> This patch adds trace events for the allocation and freeing of pages,
> including the freeing of pagevecs. Using the events, it will be known what
> struct page and pfns are being allocated and freed and what the call site
> was in many cases.
>
> The page alloc tracepoints be used as an indicator as to whether the workload
> was heavily dependant on the page allocator or not. You can make a guess based
> on vmstat but you can't get a per-process breakdown. Depending on the call
> path, the call_site for page allocation may be __get_free_pages() instead
> of a useful callsite. Instead of passing down a return address similar to
> slab debugging, the user should enable the stacktrace and seg-addr options
> to get a proper stack trace.
>
> The pagevec free tracepoint has a different usecase. It can be used to get
> a idea of how many pages are being dumped off the LRU and whether it is
> kswapd doing the work or a process doing direct reclaim.
>
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Rik van Riel <riel@redhat.com>
> ---
> include/trace/events/kmem.h | 86 +++++++++++++++++++++++++++++++++++++++++++
> mm/page_alloc.c | 6 ++-
> 2 files changed, 91 insertions(+), 1 deletions(-)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 1493c54..57bf13c 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -225,6 +225,92 @@ TRACE_EVENT(kmem_cache_free,
>
> TP_printk("call_site=%lx ptr=%p", __entry->call_site, __entry->ptr)
> );
> +
> +TRACE_EVENT(mm_page_free_direct,
> +
> + TP_PROTO(unsigned long call_site, const void *page, unsigned int order),
> +
> + TP_ARGS(call_site, page, order),
> +
> + TP_STRUCT__entry(
> + __field( unsigned long, call_site )
> + __field( const void *, page )

Why void? Is there any benefit?

> + __field( unsigned int, order )
> + ),
> +
> + TP_fast_assign(
> + __entry->call_site = call_site;
> + __entry->page = page;
> + __entry->order = order;
> + ),
> +
> + TP_printk("call_site=%lx page=%p pfn=%lu order=%d",
> + __entry->call_site,
> + __entry->page,
> + page_to_pfn((struct page *)__entry->page),
> + __entry->order)
> +);
> +
> +TRACE_EVENT(mm_pagevec_free,
> +
> + TP_PROTO(unsigned long call_site, const void *page, int order, int cold),
> +
> + TP_ARGS(call_site, page, order, cold),
> +
> + TP_STRUCT__entry(
> + __field( unsigned long, call_site )
> + __field( const void *, page )
> + __field( int, order )
> + __field( int, cold )
> + ),
> +
> + TP_fast_assign(
> + __entry->call_site = call_site;
> + __entry->page = page;
> + __entry->order = order;
> + __entry->cold = cold;
> + ),
> +
> + TP_printk("call_site=%lx page=%p pfn=%lu order=%d cold=%d",
> + __entry->call_site,
> + __entry->page,
> + page_to_pfn((struct page *)__entry->page),
> + __entry->order,
> + __entry->cold)
> +);
> +
> +TRACE_EVENT(mm_page_alloc,
> +
> + TP_PROTO(unsigned long call_site, const void *page, unsigned int order,
> + gfp_t gfp_flags, int migratetype),
> +
> + TP_ARGS(call_site, page, order, gfp_flags, migratetype),
> +
> + TP_STRUCT__entry(
> + __field( unsigned long, call_site )
> + __field( const void *, page )
> + __field( unsigned int, order )
> + __field( gfp_t, gfp_flags )
> + __field( int, migratetype )
> + ),
> +
> + TP_fast_assign(
> + __entry->call_site = call_site;
> + __entry->page = page;
> + __entry->order = order;
> + __entry->gfp_flags = gfp_flags;
> + __entry->migratetype = migratetype;
> + ),
> +
> + TP_printk("call_site=%lx page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s",
> + __entry->call_site,
> + __entry->page,
> + page_to_pfn((struct page *)__entry->page),
> + __entry->order,
> + __entry->migratetype,
> + show_gfp_flags(__entry->gfp_flags))
> +);
> +
> #endif /* _TRACE_KMEM_H */
>
> /* This part must be outside protection */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d052abb..843bdec 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1905,6 +1905,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
> zonelist, high_zoneidx, nodemask,
> preferred_zone, migratetype);
>
> + trace_mm_page_alloc(_RET_IP_, page, order, gfp_mask, migratetype);
> return page;
> }

In almost case, __alloc_pages_nodemask() is called from alloc_pages_current().
Can you add call_site argument? (likes slab_alloc)

> EXPORT_SYMBOL(__alloc_pages_nodemask);
> @@ -1945,13 +1946,16 @@ void __pagevec_free(struct pagevec *pvec)
> {
> int i = pagevec_count(pvec);
>
> - while (--i >= 0)
> + while (--i >= 0) {
> + trace_mm_pagevec_free(_RET_IP_, pvec->pages[i], 0, pvec->cold);
> free_hot_cold_page(pvec->pages[i], pvec->cold);
> + }
> }

This _RET_IP_ assume pagevec_free() is inlined function. Then,
pagevec_free() sould also change always_inline?

Yeah, I agree this is theoretical issue. but it improve readability and
studying author's intention.

> void __free_pages(struct page *page, unsigned int order)
> {
> if (put_page_testzero(page)) {
> + trace_mm_page_free_direct(_RET_IP_, page, order);
> if (order == 0)
> free_hot_page(page);
> else

This patch covered free_pages() and __pagevec_free() case.
but it doesn't cover free_hot_page() direct call.

(Fortunately, there is no free_cold_page() caller)