[PATCH 1/2] arm64: mm: Enable CONT_SIZE aligned sections for 64k page kernels.

On 02/12/2016 10:28 AM, Ard Biesheuvel wrote:

On 12 February 2016 at 17:21, Jeremy Linton [off-list ref] wrote:

quoted

On 02/12/2016 10:11 AM, Ard Biesheuvel wrote:

quoted

On 12 February 2016 at 17:06, Jeremy Linton [off-list ref] wrote:

(trimming)

quoted

quoted

   #if defined(CONFIG_DEBUG_ALIGN_RODATA)
-#define ALIGN_DEBUG_RO                 . = ALIGN(1<<SECTION_SHIFT);
-#define ALIGN_DEBUG_RO_MIN(min)                ALIGN_DEBUG_RO
+#if defined(CONFIG_ARM64_64K_PAGES)
+#define ALIGN_DEBUG_RO_MIN(min)                . = ALIGN(CONT_SIZE);
+#else
+#define ALIGN_DEBUG_RO_MIN(min)                . = ALIGN(SECTION_SIZE);

Doesn't this align to 32 MB on 16k pages kernels?

Yes, I considered whether it was more appropriate to use CONT_SIZE for 16k
as well.

Opinions?

Looking at vmlinux.lds.S, I see that that would put _stext and
__init_begin at 32 MB aligned boundaries. making the size of the
kernel at least 64 MB. If I take your .rodata patch into account,
which adds a third instance of ALIGN_DEBUG_RO_MIN, the Image footprint
will rise to ~100 MB. Or am I missing something?

No, I think your correct. But, its an option, and it sort of depends on 
use case. In a system with 100+GB of RAM it might be useful. Not so much 
on a phone or small embedded system. I don't really see those people 
enabling ALIGN_RODATA anyway. Worse, I expect the loss of RAM 
efficiently going from 4k-16k pages in a RAM constrained system to be a 
pretty big hit too.

I don't have any hard data one way or the other, and I don't have a 
strong opinion. Although, I suspect at the moment the potential users of 
16k pages may tend toward the small side.