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

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Date:   Mon, 22 Jan 2018 09:02:57 -0800
From:   Todd Kjos <tkjos@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Ganesh Mahendran <opensource.ganesh@...il.com>,
        Martijn Coenen <maco@...roid.com>,
        Arve Hjønnevåg <arve@...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 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?

>
> thanks,
>
> greg k-h