linux-kernel - Re: [PATCH 2/7] mm, vmscan: add active list aging tracepoint

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Date:   Thu, 29 Dec 2016 08:52:46 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/7] mm, vmscan: add active list aging tracepoint

On Thu 29-12-16 14:33:59, Minchan Kim wrote:
> On Wed, Dec 28, 2016 at 04:30:27PM +0100, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Our reclaim process has several tracepoints to tell us more about how
> > things are progressing. We are, however, missing a tracepoint to track
> > active list aging. Introduce mm_vmscan_lru_shrink_active which reports
> > the number of scanned, rotated, deactivated and freed pages from the
> > particular node's active list.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > ---
> >  include/linux/gfp.h           |  2 +-
> >  include/trace/events/vmscan.h | 38 ++++++++++++++++++++++++++++++++++++++
> >  mm/page_alloc.c               |  6 +++++-
> >  mm/vmscan.c                   | 22 +++++++++++++++++-----
> >  4 files changed, 61 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 4175dca4ac39..61aa9b49e86d 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -503,7 +503,7 @@ void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask);
> >  extern void __free_pages(struct page *page, unsigned int order);
> >  extern void free_pages(unsigned long addr, unsigned int order);
> >  extern void free_hot_cold_page(struct page *page, bool cold);
> > -extern void free_hot_cold_page_list(struct list_head *list, bool cold);
> > +extern int free_hot_cold_page_list(struct list_head *list, bool cold);
> >  
> >  struct page_frag_cache;
> >  extern void __page_frag_drain(struct page *page, unsigned int order,
> > diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> > index 39bad8921ca1..d34cc0ced2be 100644
> > --- a/include/trace/events/vmscan.h
> > +++ b/include/trace/events/vmscan.h
> > @@ -363,6 +363,44 @@ TRACE_EVENT(mm_vmscan_lru_shrink_inactive,
> >  		show_reclaim_flags(__entry->reclaim_flags))
> >  );
> >  
> > +TRACE_EVENT(mm_vmscan_lru_shrink_active,
> > +
> > +	TP_PROTO(int nid, unsigned long nr_scanned, unsigned long nr_freed,
> > +		unsigned long nr_unevictable, unsigned long nr_deactivated,
> > +		unsigned long nr_rotated, int priority, int file),
> > +
> > +	TP_ARGS(nid, nr_scanned, nr_freed, nr_unevictable, nr_deactivated, nr_rotated, priority, file),
> 
> I agree it is helpful. And it was when I investigated aging problem of 32bit
> when node-lru was introduced. However, the question is we really need all those
> kinds of information? just enough with nr_taken, nr_deactivated, priority, file?

Dunno. Is it harmful to add this information? I like it more when the
numbers just add up and you have a clear picture. You never know what
might be useful when debugging a weird behavior. 

[...]
> > -	move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
> > -	move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
> > +	nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
> 
> Who use nr_active in here?

this is an omission. I just forgot to add it... Thanks for noticing.

-- 
Michal Hocko
SUSE Labs