linux-kernel - Re: [PATCH] mm: vmscan: show zone type in kswapd tracepoints

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Date:   Tue, 12 Mar 2019 19:04:43 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, shaoyafang@...iglobal.com
Subject: Re: [PATCH] mm: vmscan: show zone type in kswapd tracepoints

On Mon, Mar 11, 2019 at 4:47 PM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Fri 01-03-19 15:38:54, Yafang Shao wrote:
> > If we want to know the zone type, we have to check whether
> > CONFIG_ZONE_DMA, CONFIG_ZONE_DMA32 and CONFIG_HIGHMEM are set or not,
> > that's not so convenient.
> >
> > We'd better show the zone type directly.
>
> I do agree that zone number is quite PITA to process in general but do
> we really need this information in the first place? Why do we even care?
>

Sometimes we want to know this event occurs in which zone, then we can
get the information of this zone,
for example via /proc/zoneinfo.
It could give us more information for debugging.


> Zones are an MM internal implementation details and the more we export
> to the userspace the more we are going to argue about breaking userspace
> when touching them. So I would rather not export that information unless
> it is terribly useful.
>

I 'm not sure whether zone type is  terribly useful or not, but the
'zid' is useless at all.

I don't agree that Zones are MM internal.
We can get the zone type in many ways, for example /proc/zoneinfo.

If we show this event occurs in which zone, we'd better show the zone type,
or we should drop this 'zid'.


> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > ---
> >  include/trace/events/vmscan.h | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> > index a1cb913..4c8880b 100644
> > --- a/include/trace/events/vmscan.h
> > +++ b/include/trace/events/vmscan.h
> > @@ -73,7 +73,10 @@
> >               __entry->order  = order;
> >       ),
> >
> > -     TP_printk("nid=%d zid=%d order=%d", __entry->nid, __entry->zid, __entry->order)
> > +     TP_printk("nid=%d zid=%-8s order=%d",
> > +             __entry->nid,
> > +             __print_symbolic(__entry->zid, ZONE_TYPE),
> > +             __entry->order)
> >  );
> >
> >  TRACE_EVENT(mm_vmscan_wakeup_kswapd,
> > @@ -96,9 +99,9 @@
> >               __entry->gfp_flags      = gfp_flags;
> >       ),
> >
> > -     TP_printk("nid=%d zid=%d order=%d gfp_flags=%s",
> > +     TP_printk("nid=%d zid=%-8s order=%d gfp_flags=%s",
> >               __entry->nid,
> > -             __entry->zid,
> > +             __print_symbolic(__entry->zid, ZONE_TYPE),
> >               __entry->order,
> >               show_gfp_flags(__entry->gfp_flags))
> >  );
> > --
> > 1.8.3.1
> >
>
> --
> Michal Hocko
> SUSE Labs