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

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Date:   Mon, 22 Jan 2018 16:54:28 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:     maco@...roid.com, tkjos@...gle.com, arve@...roid.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] android: binder: use VM_ALLOC to get vm area

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?

thanks,

greg k-h