linux-kernel - Re: [PATCH v2] mm: page_alloc: dump migrate-failed pages

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Message-ID: <20210310132623.GO3479805@casper.infradead.org>
Date:   Wed, 10 Mar 2021 13:26:23 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        John Dias <joaodias@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH v2] mm: page_alloc: dump migrate-failed pages

On Tue, Mar 09, 2021 at 10:32:51AM +0100, Michal Hocko wrote:
> Apart from the above, do we have to warn for something that is a
> debugging aid? A similar concern wrt dump_page which uses pr_warn and
> page owner is using even pr_alert.
> Would it make sense to add a loglevel parameter both into __dump_page
> and dump_page_owner?

No.  What would make sense is turning __dump_page() inside-out.
Something like printk("%pP\n");

In lib/vsprintf.c, there's a big switch statement in the function
pointer() that handles printing things like IPv6 addresses, dentries,
and function symbols.

Then we can do whatever we want around the new %pP, including choosing
the log level, adding additional information, choosing to dump the page
to a sysfs file, etc, etc.