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 15:34:19 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Yafang Shao <laoar.shao@...il.com>, vbabka@...e.cz,
        linmiaohe@...wei.com, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, linux@...musvillemoes.dk,
        linux-mm@...ck.org, 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 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.

-- 
With Best Regards,
Andy Shevchenko