linux-kernel - Re: [PATCH v2] mm: add VM_STATIC flag to vmalloc and prevent from removing the areas

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Date:   Wed, 19 Apr 2017 14:32:14 +0900
From:   Hoeun Ryu <hoeun.ryu@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     hch@...radead.org, khandual@...ux.vnet.ibm.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Pen <r.peniaev@...il.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Ingo Molnar <mingo@...nel.org>, zijun_hu <zijun_hu@....com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: add VM_STATIC flag to vmalloc and prevent from removing the areas


> On Apr 18, 2017, at 3:59 PM, Michal Hocko <mhocko@...nel.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