On Mon, Mar 29, 2021 at 09:34:31AM +0300, Leon Romanovsky wrote:

On Mon, Mar 29, 2021 at 02:29:10PM +0900, Hyunsoon Kim wrote:

quoted

This patch allows programmer to avoid zero initialization on page
allocation even when the kernel config "CONFIG_INIT_ON_ALLOC_DEFAULT"
is enabled. The configuration is made to prevent uninitialized
heap memory flaws, and Android has applied this for security and
deterministic execution times. Please refer to below.

https://android-review.googlesource.com/c/kernel/common/+/1235132

However, there is a case that the zeroing page memory is unnecessary
when the page is used on specific purpose and will be zeroed
automatically by hardware that accesses the memory through DMA.
For instance, page allocation used for IP packet reception from Exynos
modem is solely used for packet reception. Although the page will be
freed eventually and reused for some other purpose, initialization at
that moment of reuse will be sufficient to avoid uninitialized heap
memory flaws. To support this kind of control, this patch creates new
gfp type called ___GFP_NOINIT, that allows no zeroing at the moment
of page allocation, called by many related APIs such as page_frag_alloc,
alloc_pages, etc.

Signed-off-by: Hyunsoon Kim <redacted>
---
 include/linux/gfp.h | 2 ++
 include/linux/mm.h  | 4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

Let's assume that we will use this new flag, and users are smart enough
to figure when it needs to be used, what will be the performance gain?

Thanks

For instance, there are four memory access (either read or write) done
by the system; memory write due to page allocation for reserving memory
for modem hardware, memory write on the page by modem hardware,
read and write incurred by copy_to_user operation by iperf reading
the incoming network data. Theoretically, we can expect 1/4 of power
saving on DRAM bandwidth. By performing simple iperf test with download
UDP 800Mbps, we saw 5-6mA power gain by disabling
CONFIG_INIT_ON_ALLOC_DEFAULT.

Thanks