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Subject: Re: [PATCH v2] mm: add VM_STATIC flag to vmalloc and prevent from removing the areas
From: Hoeun Ryu <hoeun.ryu@gmail.com>
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Date: Wed, 19 Apr 2017 14:32:14 +0900
Cc: hch@infradead.org, khandual@linux.vnet.ibm.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Pen <r.peniaev@gmail.com>, Andreas Dilger <adilger@dilger.ca>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Ingo Molnar <mingo@kernel.org>, zijun_hu <zijun_hu@htc.com>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        Thomas Garnier <thgarnie@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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To: Michal Hocko <mhocko@kernel.org>
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> On Apr 18, 2017, at 3:59 PM, Michal Hocko <mhocko@kernel.org> wrote:
> 
>> On Tue 18-04-17 14:48:39, Hoeun Ryu wrote:
>> vm_area_add_early/vm_area_register_early() are used to reserve vmalloc area
>> during boot process and those virtually mapped areas are never unmapped.
>> So `OR` VM_STATIC flag to the areas in vmalloc_init() when importing
>> existing vmlist entries and prevent those areas from being removed from the
>> rbtree by accident.
> 
> Has this been a problem in the past or currently so that it is worth
> handling?
> 
>> This flags can be also used by other vmalloc APIs to
>> specify that the area will never go away.
> 
> Do we have a user for that?
> 
>> This makes remove_vm_area() more robust against other kind of errors (eg.
>> programming errors).
> 
> Well, yes it will help to prevent from vfree(early_mem) but we have 4
> users of vm_area_register_early so I am really wondering whether this is
> worth additional code. It would really help to understand your
> motivation for the patch if we were explicit about the problem you are
> trying to solve.

I just think that it would be good to make it robust against various kind of errors.
You might think that's not an enough reason to do so though.

> 
> Thanks
> 
> -- 
> Michal Hocko
> SUSE Labs