linux-kernel - Re: [PATCH v2 3/3] vsprintf: dump full information of page flags in pGp

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Date:   Mon, 1 Feb 2021 21:52:53 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Christoph Lameter <cl@...ux.com>, penberg@...nel.org,
        David Rientjes <rientjes@...gle.com>, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v2 3/3] vsprintf: dump full information of page flags in pGp

On Mon, Feb 1, 2021 at 9:34 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Feb 01, 2021 at 02:23:33PM +0100, David Hildenbrand wrote:
> > On 01.02.21 12:56, Yafang Shao wrote:
> > > Currently the pGp only shows the names of page flags, rather than
> > > the full information including section, node, zone, last cpupid and
> > > kasan tag. While it is not easy to parse these information manually
> > > because there're so many flavors. Let's interpret them in pGp as well.
> > >
> > > - Before the patch,
> > > [ 6343.396602] Slab 0x000000004382e02b objects=33 used=3 fp=0x000000009ae06ffc flags=0x17ffffc0010200(slab|head)
> > >
> > > - After the patch,
> > > [ 6871.296131] Slab 0x00000000c0e19a37 objects=33 used=3 fp=0x00000000c4902159 flags=0x17ffffc0010200(Node 0,Zone 2,Lastcpupid 0x1fffff,slab|head)
> >
> > For debugging purposes, it might be helpful to have the actual zone name
> > (and to know if the value is sane). You could obtain it (without other
> > modifications) via
> >
> > const char zname = "Invalid";
> >
> > if (zone < MAX_NR_ZONES)
> >       zname = first_online_pgdat()->node_zones[zone].name;
> >
> >
> > Similarly, it might also be helpful to indicate if a node is
> > online/offline/invalid/.
> >
> > const char nstate = "Invalid";
> >
> > if (node_online(nid))
> >       nstate = "Online";
> > else if (node_possible(nid))
> >       nstate = "Offline";
> >
> >
> > Printing that in addition to the raw value could be helpful. Just some
> > thoughts.
>
> printf() buffer is not a black hole, esp. when you get it messed with critical
> messages (Oops). I suggest to reduce a burden as much as possible. If you wish
> to get this, make it caller-configurable, i.e. adding another letter to the
> specifier.
>

I think David's suggestion will help us to identify issues.

You mean that we should use another one like "%pGpd" - means pGp debug
- to implement it ?

-- 
Thanks
Yafang