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

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Message-ID: <YEjpj9g32ApZFY6u@google.com>
Date:   Wed, 10 Mar 2021 07:45:19 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        John Dias <joaodias@...gle.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH v2] mm: page_alloc: dump migrate-failed pages

On Wed, Mar 10, 2021 at 09:20:40AM +0100, David Hildenbrand wrote:
> On 10.03.21 08:42, Minchan Kim wrote:
> > On Tue, Mar 09, 2021 at 08:15:41AM -0800, Minchan Kim wrote:
> > 
> > < snip >
> > 
> > > > [...]
> > > > > +void dump_migrate_failure_pages(struct list_head *page_list)
> > > > > +{
> > > > > +	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor,
> > > > > +			"migrate failure");
> > > > > +	if (DYNAMIC_DEBUG_BRANCH(descriptor) &&
> > > > > +			alloc_contig_ratelimit()) {
> > > > > +		struct page *page;
> > > > > +
> > > > > +		WARN(1, "failed callstack");
> > > > > +		list_for_each_entry(page, page_list, lru)
> > > > > +			dump_page(page, "migration failure");
> > > > > +	}
> > > > 
> > > > 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
> > > 
> > > Make sense.
> > > 
> > > > page owner is using even pr_alert.
> > > > Would it make sense to add a loglevel parameter both into __dump_page
> > > > and dump_page_owner?
> > > 
> > > Let me try it.
> > 
> > I looked though them and made first draft to clean them up.
> > 
> > It's bigger than my initial expectaion because there are many callsites
> > to use dump_page and stack_trace_print inconsistent loglevel.
> > Since it's not a specific problem for this work, I'd like to deal with
> > it as separate patchset since I don't want to be stuck on here for my
> > initial goal.
> 
> Why the need to rush regarding your series?
> 
> If it will clean up your patch significantly, then I think doing the
> cleanups first is the proper way to go.

It doesn't clean up my patch at all. dump_page and internal functions
are already broken in several places from print level point of view.

I agreed that it's good to fix but it shouldn't be a block for the work
since it's not a new particular problem this patch introduce.

> 
> I really don't get why this is a real problem.

That's because it's not my top priority.