linux-kernel - Re: [PATCH v7 3/4] mm,page_owner: Display all stacks and their count

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Date: Mon, 12 Feb 2024 11:47:01 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Oscar Salvador <osalvador@...e.de>, Marco Elver <elver@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>,
 Andrey Konovalov <andreyknvl@...il.com>,
 Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v7 3/4] mm,page_owner: Display all stacks and their count

On 2/11/24 21:39, Oscar Salvador wrote:
> On Sat, Feb 10, 2024 at 08:52:25AM +0100, Marco Elver wrote:
>> The extra bits are used by KMSAN, and might conflict if enabled at the
>> same time. I think the safest option is to keep your own list. I think
>> that will also be more performant if there are other stackdepot users
>> because you do not have to traverse any of the other entries.
> 
> Ok, I thought we had spare bits for other users.
> But thinking about it some more, yes, it makes sense for page_owner to
> maintain its own list, so traversing it is faster and we do not have
> to place code to traverse the buckets in stackdepot.

Would it make sense to introduce per-user stack depot instances? ("user"
being a subsystem i.e. kasan or page_owner). I'd expect each to have a
distinct set of stacks, so there's no benefits of using the same hash table,
only downsides of longer collision lists?

I can imagine this would be easier for users that don't need the early init
kind of stackdepot, but maybe even there it could be feasible to have a
small fixed size array of hash table roots and every user would get a
separate index?