linux-kernel - Re: [PATCH] mm/kmemleak: Add cond_resched() to kmemleak_free

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Message-ID: <ZWh-LLuTeAGzY3lM@arm.com>
Date:   Thu, 30 Nov 2023 12:21:00 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Waiman Long <longman@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/kmemleak: Add cond_resched() to kmemleak_free_percpu()

On Wed, Nov 29, 2023 at 05:57:11PM -0500, Waiman Long wrote:
> On 11/28/23 11:04, Catalin Marinas wrote:
> > The problem is looking up the object tree for each per-cpu offset. We
> > can make the percpu pointer handling O(1) since freeing is only done by
> > the main __percpu pointer, so that's the only one needing a look-up. So
> > far the per-cpu pointers are not tracked for leaking, only scanned.
> > 
> > We could just add the per_cpu_ptr(ptr, 0) to the kmemleak
> > object_tree_root but when scanning we don't have an inverse function to
> > get the __percpu pointer back and calculate the pointers for the other
> > CPUs (well, we could with some hacks but they are probably fragile).
> > 
> > What I came up with is a separate object_percpu_tree_root similar to the
> > object_phys_tree_root. The only reason for these additional trees is to
> > look up the kmemleak metadata when needed (usually freeing). They don't
> > contain objects that are tracked for actual leaking, only scanned. A
> > briefly tested patch below. I need to go through it again, update some
> > comments and write a commit log:
[...]
> The patch looks reasonable to me. It also has a side effect of reducing the
> # of kmemleak objects to track especially for system with large number of
> CPUs. Of course, we still need more testing to make sure that it won't break
> anything.

Thanks for having a look. I'll tidy it up and post today or tomorrow. It
can stay in next for a bit before upstreaming to get some exposure
(though not sure many test -next with kmemleak enabled).

-- 
Catalin