linux-kernel - Re: [PATCH v2 2/3] mm, page_owner: Add page_owner_stacks file to print out only stacks and their counter

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Date:   Mon, 5 Sep 2022 15:00:24 +0200
From:   Marco Elver <elver@...gle.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Eric Dumazet <edumazet@...gle.com>,
        Waiman Long <longman@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v2 2/3] mm, page_owner: Add page_owner_stacks file to
 print out only stacks and their counter

On Mon, Sep 05, 2022 at 02:57PM +0200, Marco Elver wrote:
[...]
> > +{
> > +	int i = *pos, ret = 0;
> > +	struct stack_record **stacks, *stack;
> > +	static struct stack_record *last = NULL;
> > +	unsigned long stack_table_entries = stack_hash_mask + 1;
> > +
> > +	/* Continue from the last stack if we have one */
> > +	if (last) {
> > +		stack = last->next;
> 
> This is dead code?

Oof, I just noticed that 'last' is static. Please avoid that, because
it'll make this interface really tricky to use safely. I still don't
quite understand why it needs to do this, and a kernel-doc comment would
make this clearer.