linux-kernel - Re: [PATCH v4 10/17] mm/slab: kmalloc: pass requests larger than order-1 page to page allocator

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Message-ID: <Y0n1WxxwbgSOmMwJ@hyeyoo>
Date:   Sat, 15 Oct 2022 08:48:43 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/17] mm/slab: kmalloc: pass requests larger than
 order-1 page to page allocator

On Fri, Oct 14, 2022 at 01:58:18PM -0700, Guenter Roeck wrote:
> Hi,
> 
> On Wed, Aug 17, 2022 at 07:18:19PM +0900, Hyeonggon Yoo wrote:
> > There is not much benefit for serving large objects in kmalloc().
> > Let's pass large requests to page allocator like SLUB for better
> > maintenance of common code.
> > 
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> > Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> > ---
> 
> This patch results in a WARNING backtrace in all mips and sparc64
> emulations.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 0 at mm/slab_common.c:729 kmalloc_slab+0xc0/0xdc
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 6.0.0-11990-g9c9155a3509a #1
> Stack : ffffffff 801b2a18 80dd0000 00000004 00000000 00000000 81023cd4 00000000
>         81040000 811a9930 81040000 8104a628 81101833 00000001 81023c78 00000000
>         00000000 00000000 80f5d858 81023b98 00000001 00000023 00000000 ffffffff
>         00000000 00000064 00000002 81040000 81040000 00000001 80f5d858 000002d9
>         00000000 00000000 80000000 80002000 00000000 00000000 00000000 00000000
>         ...
> Call Trace:
> [<8010a2bc>] show_stack+0x38/0x118
> [<80cf5f7c>] dump_stack_lvl+0xac/0x104
> [<80130d7c>] __warn+0xe0/0x224
> [<80cdba5c>] warn_slowpath_fmt+0x64/0xb8
> [<8028c058>] kmalloc_slab+0xc0/0xdc
> 
> irq event stamp: 0
> hardirqs last  enabled at (0): [<00000000>] 0x0
> hardirqs last disabled at (0): [<00000000>] 0x0
> softirqs last  enabled at (0): [<00000000>] 0x0
> softirqs last disabled at (0): [<00000000>] 0x0
> ---[ end trace 0000000000000000 ]---
> 
> Guenter

Hi.

Thank you so much for this report!

Hmm so SLAB tries to find kmalloc cache for freelist index array using
kmalloc_slab() directly, and it becomes problematic when size of the
array is larger than PAGE_SIZE * 2.

Will send a fix soon.

-- 
Thanks,
Hyeonggon