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: > > 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 <h10.kim@xxxxxxxxxxx> > > --- > > 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
