linux-kernel - Re: [PATCH v8 2/5] mm,page_owner: Implement the tracking of the stacks count

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Message-ID: <ZcuK2I6ZwFwFX-G5@localhost.localdomain>
Date: Tue, 13 Feb 2024 16:29:28 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>,
	Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v8 2/5] mm,page_owner: Implement the tracking of the
 stacks count

On Tue, Feb 13, 2024 at 02:42:25PM +0100, Vlastimil Babka wrote:
> On 2/12/24 23:30, Oscar Salvador wrote:
> >  	__set_page_owner_handle(page_ext, handle, order, gfp_mask);
> >  	page_ext_put(page_ext);
> > +	inc_stack_record_count(handle);
> 
> What if this is dummy handle, which means we have recursed in page owner,
> and we'll by trying to kmalloc() its struct stack and link it to the
> stack_list because it was returned for the first time? Also failure_handle.
> Could you pre-create static (not kmalloc) struct stack for these handles
> with refcount of 0 and insert them to stack_list, all during
> init_page_owner()? Bonus: no longer treating stack_list == NULL in a special
> way in add_stack_record_to_list() (although you don't need to handle it
> extra even now, AFAICS).

Good catch. I did not think about this scenario, but this could
definitely happen.
Yeah, maybe creating an array of 2 structs for {dummy,failure}_handle
and link them into stack_list.

I thought about giving them a refcount of 1, because we only print
stacks which refcount > 1 anyways, but setting it to 0 has comes with
the advantage of catching spurious increments, should someone call
refcount_inc on those (which should not really happen).

I will try to implement it.

Thanks

-- 
Oscar Salvador
SUSE Labs