linux-kernel - Re: [PATCH] mm: fix printk format within cma

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Date:   Tue, 18 Apr 2023 12:33:38 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Zhaoyang Huang <huangzhaoyang@...il.com>, ke.wang@...soc.com
Subject: Re: [PATCH] mm: fix printk format within cma

On Tue, 18 Apr 2023 04:38:24 +0100 Matthew Wilcox <willy@...radead.org> wrote:

> On Tue, Apr 18, 2023 at 11:33:09AM +0800, zhaoyang.huang wrote:
> > cma and page pointer printed via %p are hash value which make debug to be hard.
> > change them to %px.
> 
> Why does printing the page pointer make any sense at all?  Surely the
> PFN makes much more sense.

I suppose one could correlate a particular hashed pointer with other
debug output, see "ah, that's the same page".  In which case one
doesn't really care whether or not the address is hashed - it's just a
cookie.  This sounds thin.

I doubt if a lot of thought went into the printk.  If the page pointer
isn't useful then how about we simply remove it from the message?