On 03/14/2016 08:18 AM, Joonsoo Kim wrote:

On Mon, Mar 14, 2016 at 08:06:16AM +0100, Vlastimil Babka wrote:

quoted

On 03/14/2016 07:49 AM, Joonsoo Kim wrote:

quoted

On Fri, Mar 11, 2016 at 06:07:40PM +0100, Vlastimil Babka wrote:

quoted

On 03/11/2016 04:00 PM, Joonsoo Kim wrote:

How about something like this? Just and idea, probably buggy (off-by-one etc.).
Should keep away cost from <pageblock_order iterations@the expense of the
relatively fewer >pageblock_order iterations.

Hmm... I tested this and found that it's code size is a little bit
larger than mine. I'm not sure why this happens exactly but I guess it would be
related to compiler optimization. In this case, I'm in favor of my
implementation because it looks like well abstraction. It adds one
unlikely branch to the merge loop but compiler would optimize it to
check it once.

I would be surprised if compiler optimized that to check it once, as
order increases with each loop iteration. But maybe it's smart
enough to do something like I did by hand? Guess I'll check the
disassembly.

Okay. I used following slightly optimized version and I need to
add 'max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1)'
to yours. Please consider it, too.

Hmm, so this is bloat-o-meter on x86_64, gcc 5.3.1. CONFIG_CMA=y

next-20160310 vs my patch (with added min_t as you pointed out):
add/remove: 0/0 grow/shrink: 1/1 up/down: 69/-5 (64)
function                                     old     new   delta
free_one_page                                833     902     +69
free_pcppages_bulk                          1333    1328      -5

next-20160310 vs your patch:
add/remove: 0/0 grow/shrink: 2/0 up/down: 577/0 (577)
function                                     old     new   delta
free_one_page                                833    1187    +354
free_pcppages_bulk                          1333    1556    +223

my patch vs your patch:
add/remove: 0/0 grow/shrink: 2/0 up/down: 513/0 (513)
function                                     old     new   delta
free_one_page                                902    1187    +285
free_pcppages_bulk                          1328    1556    +228

The increase of your version is surprising, wonder what the compiler 
did. Otherwise I would like simpler/maintainable version, but this is crazy.
Can you post your results? I wonder if your compiler e.g. decided to 
stop inlining page_is_buddy() or something.