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

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Date:   Wed, 31 Jul 2019 10:53:56 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <cai@....pw>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] mm: kmemleak: Use mempool allocations for kmemleak
 objects

On Tue, Jul 30, 2019 at 04:22:37PM -0400, Qian Cai wrote:
> On Tue, 2019-07-30 at 12:57 -0700, Andrew Morton wrote:
> > On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas <catalin.marinas@....com>
> > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > @@ -2011,6 +2011,12 @@
> > >  			Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
> > >  			the default is off.
> > >  
> > > +	kmemleak.mempool=
> > > +			[KNL] Boot-time tuning of the minimum kmemleak
> > > +			metadata pool size.
> > > +			Format: <int>
> > > +			Default: NR_CPUS * 4
> > > +
> 
> Catalin, BTW, it is right now unable to handle a large size. I tried to reserve
> 64M (kmemleak.mempool=67108864),
> 
> [    0.039254][    T0] WARNING: CPU: 0 PID: 0 at mm/page_alloc.c:4707 __alloc_pages_nodemask+0x3b8/0x1780
[...]
> [    0.039646][    T0] NIP [c000000000395038] __alloc_pages_nodemask+0x3b8/0x1780
> [    0.039693][    T0] LR [c0000000003d9320] kmalloc_large_node+0x100/0x1a0
> [    0.039727][    T0] Call Trace:
> [    0.039795][    T0] [c00000000170fc80] [c0000000003e5080] __kmalloc_node+0x520/0x890
> [    0.039816][    T0] [c00000000170fd20] [c0000000002e9544] mempool_init_node+0xb4/0x1e0
> [    0.039836][    T0] [c00000000170fd80] [c0000000002e975c] mempool_create_node+0xcc/0x150
> [    0.039857][    T0] [c00000000170fdf0] [c000000000b2a730] kmemleak_init+0x16c/0x54c
> [    0.039878][    T0] [c00000000170fef0] [c000000000ae460c] start_kernel+0x69c/0x7cc
> [    0.039908][    T0] [c00000000170ff90] [c00000000000a7d4] start_here_common+0x1c/0x434
[...]
> [    0.040100][    T0] kmemleak: Kernel memory leak detector disabled

It looks like the mempool cannot be created. 64M objects means a
kmalloc(512MB) for the pool array in mempool_init_node(), so that hits
the MAX_ORDER warning in __alloc_pages_nodemask().

Maybe the mempool tunable won't help much for your case if you need so
many objects. It's still worth having a mempool for kmemleak but we
could look into changing the refill logic while keeping the original
size constant (say 1024 objects).

> [   16.192449][    T1] BUG: Unable to handle kernel data access at 0xffffffffffffb2aa

This doesn't seem kmemleak related from the trace.

-- 
Catalin