linux-kernel - Re: [PATCH] mm/vmalloc: add vm_struct for vm_map

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Date:   Thu, 20 Jul 2017 09:15:10 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     zhaoyang.huang@...eadtrum.com, Michal Hocko <mhocko@...e.com>,
        Ingo Molnar <mingo@...nel.org>, zijun_hu <zijun_hu@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Thomas Garnier <thgarnie@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, zijun_hu@...o.com,
        ming.ling@...eadtrum.com
Subject: Re: [PATCH] mm/vmalloc: add vm_struct for vm_map_ram area

On Thu, Jul 20, 2017 at 4:50 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 19 Jul 2017 18:44:03 +0800 Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
>
>> /proc/vmallocinfo will not show the area allocated by vm_map_ram, which
>> will make confusion when debug. Add vm_struct for them and show them in
>> proc.
>>
>
> Please provide sample /proc/vmallocinfo so we can better understand the
> proposal.  Is there a means by which people can determine that a
> particular area is from vm_map_ram()?  I don't think so.  Should there
> be?
Here is the part of vmallocinfo, the line start with '>' are the ones
allocated by vm_map_ram.
xxxx:/ # cat /proc/vmallocinfo
0xffffff8000a5f000-0xffffff8000abb000  376832
load_module+0x1004/0x1e98 pages=91 vmalloc
0xffffff8000ac6000-0xffffff8000ad2000   49152
load_module+0x1004/0x1e98 pages=11 vmalloc
0xffffff8000ad8000-0xffffff8000ade000   24576
load_module+0x1004/0x1e98 pages=5 vmalloc
0xffffff8008000000-0xffffff8008002000    8192 of_iomap+0x4c/0x68
phys=12001000 ioremap
0xffffff8008002000-0xffffff8008004000    8192 of_iomap+0x4c/0x68
phys=40356000 ioremap
0xffffff8008004000-0xffffff8008007000   12288 of_iomap+0x4c/0x68
phys=12002000 ioremap
0xffffff8008008000-0xffffff800800d000   20480
of_sprd_gates_clk_setup_with_ops+0x88/0x2a8 phys=402b0000 ioremap
0xffffff800800e000-0xffffff8008010000    8192 of_iomap+0x4c/0x68
phys=40356000 ioremap
...
>0xffffff800c5a3000-0xffffff800c5ec000  299008 shmem_ram_vmap+0xe8/0x1a0
0xffffff800c5fe000-0xffffff800c600000    8192
kbasep_js_policy_ctx_has_priority+0x254/0xdb0 [mali_kbase] pages=1
vmalloc
0xffffff800c600000-0xffffff800c701000 1052672 of_iomap+0x4c/0x68
phys=60d00000 ioremap
>0xffffff800c701000-0xffffff800c742000  266240 shmem_ram_vmap+0xe8/0x1a0
0xffffff800c74e000-0xffffff800c750000    8192
kbasep_js_policy_ctx_has_priority+0x2cc/0xdb0 [mali_kbase] pages=1
vmalloc
...
>
>>
>> ...
>>
>> @@ -1173,6 +1178,12 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t pro
>>               addr = (unsigned long)mem;
>>       } else {
>>               struct vmap_area *va;
>> +             struct vm_struct *area;
>> +
>> +             area = kzalloc_node(sizeof(*area), GFP_KERNEL, node);
>> +             if (unlikely(!area))
>> +                     return NULL;
>
> Allocating a vm_struct for each vm_map_ram area is a cost.  And we're
> doing this purely for /proc/vmallocinfo.  I think I'll need more
> persuading to convince me that this is a good tradeoff, given that
> *every* user will incur this cost, and approximately 0% of them will
> ever use /proc/vmallocinfo.
>
> So... do we *really* need this?  If so, why?
The motivation of this commit comes from one practical debug, that is,
vmalloc failed by one driver's allocating a
huge area by vm_map_ram, which can not be traced by cat
/proc/vmallocinfo. We have to add a lot of printk and
dump_stack to get more information.
I don't think the vm_struct cost too much memory, just imagine that
the area got by vmalloc or ioremap instead, you have
to pay for it as well.
>