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From:   =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>
Date:   Mon, 22 Jan 2018 10:55:17 -0800
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Subject: Re: [PATCH v3] android: binder: use VM_ALLOC to get vm area
To:     Todd Kjos <tkjos@google.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Ganesh Mahendran <opensource.ganesh@gmail.com>,
        Martijn Coenen <maco@android.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Jan 22, 2018 at 9:02 AM, Todd Kjos <tkjos@google.com> wrote:
> On Mon, Jan 22, 2018 at 7:54 AM, Greg KH <gregkh@linuxfoundation.org> wro=
te:
>> On Wed, Jan 10, 2018 at 10:49:05AM +0800, Ganesh Mahendran wrote:
>>> VM_IOREMAP is used to access hardware through a mechanism called
>>> I/O mapped memory. Android binder is a IPC machanism which will
>>> not access I/O memory.
>>>
>>> And VM_IOREMAP has alignment requiement which may not needed in
>>> binder.
>>>     __get_vm_area_node()
>>>     {
>>>     ...
>>>         if (flags & VM_IOREMAP)
>>>             align =3D 1ul << clamp_t(int, fls_long(size),
>>>                PAGE_SHIFT, IOREMAP_MAX_ORDER);
>>>     ...
>>>     }
>>>
>>> This patch will save some kernel vm area, especially for 32bit os.
>>>
>>> In 32bit OS, kernel vm area is only 240MB. We may got below
>>> error when launching a app:
>>>
>>> <3>[ 4482.440053] binder_alloc: binder_alloc_mmap_handler: 15728 8ce670=
00-8cf65000 get_vm_area failed -12
>>> <3>[ 4483.218817] binder_alloc: binder_alloc_mmap_handler: 15745 8ce670=
00-8cf65000 get_vm_area failed -12
>>>
>>> Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
>>> ----
>>> V3: update comments
>>> V2: update comments
>>> ---
>>>  drivers/android/binder_alloc.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> Martijn and Todd, any objections to this patch?
>
> Looks fine to me. Arve, do you remember the rationale for using VM_IOREMA=
P?
>

I don't remember for sure, but I think it used alloc_vm_area at some
point, and that uses VM_IOREMAP.

--=20
Arve Hj=C3=B8nnev=C3=A5g