linux-kernel - Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak objects

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Date:   Wed, 31 Jul 2019 16:44:50 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>, Qian Cai <cai@....pw>
Subject: Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak
 objects

On Tue, Jul 30, 2019 at 01:02:15PM -0700, Andrew Morton wrote:
> On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas <catalin.marinas@....com> wrote:
> 
> > Add mempool allocations for struct kmemleak_object and
> > kmemleak_scan_area as slightly more resilient than kmem_cache_alloc()
> > under memory pressure. Additionally, mask out all the gfp flags passed
> > to kmemleak other than GFP_KERNEL|GFP_ATOMIC.
> > 
> > A boot-time tuning parameter (kmemleak.mempool) is added to allow a
> > different minimum pool size (defaulting to NR_CPUS * 4).
> 
> btw, the checkpatch warnings are valid:
> 
> WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc
> #70: FILE: mm/kmemleak.c:197:
> +static int min_object_pool = NR_CPUS * 4;
> 
> WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc
> #71: FILE: mm/kmemleak.c:198:
> +static int min_scan_area_pool = NR_CPUS * 1;
> 
> There can be situations where NR_CPUS is much larger than
> num_possible_cpus().  Can we initialize these tunables within
> kmemleak_init()?

We could and, at least on arm64, cpu_possible_mask is already
initialised at that point. However, that's a totally made up number. I
think we would better go for a Kconfig option (defaulting to, say, 1024)
similar to the CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE and we grow it if
people report better values in the future.

-- 
Catalin