linux-kernel - Re: [PATCH v3] android: binder: use VM

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Date:   Mon, 22 Jan 2018 10:55:17 -0800
From:   Arve Hjønnevåg <arve@...roid.com>
To:     Todd Kjos <tkjos@...gle.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Ganesh Mahendran <opensource.ganesh@...il.com>,
        Martijn Coenen <maco@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] android: binder: use VM_ALLOC to get vm area

On Mon, Jan 22, 2018 at 9:02 AM, Todd Kjos <tkjos@...gle.com> wrote:
> On Mon, Jan 22, 2018 at 7:54 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>> 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 = 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 8ce67000-8cf65000 get_vm_area failed -12
>>> <3>[ 4483.218817] binder_alloc: binder_alloc_mmap_handler: 15745 8ce67000-8cf65000 get_vm_area failed -12
>>>
>>> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.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_IOREMAP?
>

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

-- 
Arve Hjønnevåg