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

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Date:   Tue, 30 Jul 2019 13:02:15 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Catalin Marinas <catalin.marinas@....com>
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 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()?