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

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Message-ID: <CALOAHbA6FG97tkKLJQSYocmgYRYJGa=5ULV1AK92+dw=MtKZJA@mail.gmail.com>
Date:   Tue, 12 Mar 2019 22:10:48 +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 Tue, Mar 12, 2019 at 9:38 PM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Tue 12-03-19 19:04:43, Yafang Shao wrote:
> > 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.
>
> Could you be more specific please?
>

Honestly speaking,  this one hasn't help us fix the real issue yet.

> > > 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'.
>
> Yes, I am suggesting the later. If somebody really needs it then I would
> like to see a _specific_ usecase. Then we can add the proper name.

This 'zid' always seems like a noise currently.
I will send a patch to drop this one.

Thanks
Yafang