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

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Message-ID: <20210201185940.GS308988@casper.infradead.org>
Date:   Mon, 1 Feb 2021 18:59:40 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Yafang Shao <laoar.shao@...il.com>,
        andriy.shevchenko@...ux.intel.com, david@...hat.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
Subject: Re: [PATCH v2 3/3] vsprintf: dump full information of page flags in
 pGp

On Mon, Feb 01, 2021 at 10:51:03AM -0800, Joe Perches wrote:
> On Mon, 2021-02-01 at 14:15 +0000, Matthew Wilcox wrote:
> > On Mon, Feb 01, 2021 at 07:56:10PM +0800, Yafang Shao wrote:
> > > - 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)
> > 
> > I would suggest it will be easier to parse as:
> > 
> > flags=0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
> > 
> > That should alleviate the concerns about debugfs format change -- we've
> > never guaranteed that flag names won't change, and they now look enough
> > like flags that parsers shouldn't fall over them.
> 
> Seems sensible and would make the generating code simpler too.
> 
> But is it worth the vsprintf code expansion for the 5 current uses?
> 
> mm/debug.c:     pr_warn("%sflags: %#lx(%pGp)%s\n", type, head->flags, &head->flags,
> mm/memory-failure.c:                    pr_info("soft offline: %#lx: %s migration failed %d, type %lx (%pGp)\n",
> mm/memory-failure.c:            pr_info("soft offline: %#lx: %s isolation failed, page count %d, type %lx (%pGp)\n",
> mm/memory-failure.c:            pr_info("%s: %#lx: unknown page type: %lx (%pGp)\n",
> mm/page_owner.c:                        "PFN %lu type %s Block %lu type %s Flags %#lx(%pGp)\n",
> 
> Wouldn't it be more sensible just to put this code in a new function
> call in mm?

Does it matter whether the code lives in vsprintf.c or mm/debug.c?  It's
built into the kernel core either way.  I'm not a huge fan of the current
way %pFoo is handled, but unless/until it's drastically revised, I don't
think this proposed patch makes anything worse.