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

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Message-ID: <20190312133816.GR5721@dhcp22.suse.cz>
Date:   Tue, 12 Mar 2019 14:38:16 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yafang Shao <laoar.shao@...il.com>
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 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?

> > 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.
-- 
Michal Hocko
SUSE Labs