linux-kernel - Re: [RESEND PATCH v5 3/4] mm/vmalloc: revert "mm/vmalloc.c: check VM_UNINITIALIZED flag in s_show instead of show_numa

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Date:	Tue, 17 Sep 2013 01:44:04 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"iamjoonsoo.kim" <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>,
	zhangyanfei@...fujitsu.com,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v5 3/4] mm/vmalloc: revert "mm/vmalloc.c: check
 VM_UNINITIALIZED flag in s_show instead of show_numa_info"

On Mon, Sep 16, 2013 at 8:18 PM, Wanpeng Li <liwanp@...ux.vnet.ibm.com> wrote:
> Hi KOSAKI,
> On Mon, Sep 16, 2013 at 05:23:32PM -0400, KOSAKI Motohiro wrote:
>>On 9/14/2013 7:45 PM, Wanpeng Li wrote:
>>> Changelog:
>>>  *v2 -> v3: revert commit d157a558 directly
>>>
>>> The VM_UNINITIALIZED/VM_UNLIST flag introduced by commit f5252e00(mm: avoid
>>> null pointer access in vm_struct via /proc/vmallocinfo) is used to avoid
>>> accessing the pages field with unallocated page when show_numa_info() is
>>> called. This patch move the check just before show_numa_info in order that
>>> some messages still can be dumped via /proc/vmallocinfo. This patch revert
>>> commit d157a558 (mm/vmalloc.c: check VM_UNINITIALIZED flag in s_show instead
>>> of show_numa_info);
>>
>>Both d157a558 and your patch don't explain why your one is better. Yes, some
>>messages _can_ be dumped. But why should we do so?
>
> More messages can be dumped and original commit f5252e00(mm: avoid null pointer
> access in vm_struct via /proc/vmallocinfo) do that.
>
>>And No. __get_vm_area_node() doesn't use __GFP_ZERO for allocating vm_area_struct.
>>dumped partial dump is not only partial, but also may be garbage.
>
> vm_struct is allocated by kzalloc_node.

Oops, you are right. Then, your code _intentionally_ show amazing
zero. Heh, nice.
More message is pointless. zero is just zero. It doesn't have any information.


>>I wonder why we need to call setup_vmalloc_vm() _after_ insert_vmap_area.
>
> I think it's another topic.

Why?


> Fill vm_struct and set VM_VM_AREA flag. If I misunderstand your
> question?

VM_VM_AREA doesn't help. we have race between insert_vmap_area and
setup_vmalloc_vm.
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