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SubjectRe: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()
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Hi,

Le 23/04/2022 à 12:24, Fabio M. De Francesco a écrit :
> The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
> where it is feasible. Each call of kmap_atomic() in the kernel creates
> a non-preemptible section and disable pagefaults. This could be a source
> of unwanted latency, so it should be only used if it is absolutely
> required, otherwise kmap_local_page() should be preferred.
>
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any context
> (including interrupts).
>
> Therefore, use kmap_local_page() / kunmap_local() in place of
> kmap_atomic() / kunmap_atomic().
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
> drivers/android/binder_alloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0875c463c002..058595cc7ff0 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
> page = binder_alloc_get_page(alloc, buffer,
> buffer_offset, &pgoff);
> size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> - base_ptr = kmap_atomic(page);
> + base_ptr = kmap_local_page(page);
> tmpptr = base_ptr + pgoff;
> if (to_buffer)
> memcpy(tmpptr, ptr, size);
> else
> memcpy(ptr, tmpptr, size);

in the same spirit as patch 1/3, memcpy_to_page() and memcpy_from_page()
looks good candidate to avoid code duplication.

Not checked in details, but looks mostly the same.

Just my 2c.

CJ

> /*
> - * kunmap_atomic() takes care of flushing the cache
> + * kunmap_local() takes care of flushing the cache
> * if this device has VIVT cache arch
> */
> - kunmap_atomic(base_ptr);
> + kunmap_local(base_ptr);
> bytes -= size;
> pgoff = 0;
> ptr = ptr + size;

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