Re: Suspicious error for CMA stress test

From: Vlastimil Babka
Date: Thu Mar 17 2016 - 11:43:59 EST

On 03/17/2016 10:24 AM, Hanjun Guo wrote:
On 2016/3/17 14:54, Joonsoo Kim wrote:
On Wed, Mar 16, 2016 at 05:44:28PM +0800, Hanjun Guo wrote:
On 2016/3/14 15:18, Joonsoo Kim wrote:
On Mon, Mar 14, 2016 at 08:06:16AM +0100, Vlastimil Babka wrote:
On 03/14/2016 07:49 AM, Joonsoo Kim wrote:
On Fri, Mar 11, 2016 at 06:07:40PM +0100, Vlastimil Babka wrote:
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 at 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
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, this one is not work, I still can see the bug is there after applying
this patch, did I miss something?
I may find that there is a bug which was introduced by me some time
ago. Could you test following change in __free_one_page() on top of
Vlastimil's patch?

-page_idx = pfn & ((1 << max_order) - 1);
+page_idx = pfn & ((1 << MAX_ORDER) - 1);

I tested Vlastimil's patch + your change with stress for more than half hour, the bug
I reported is gone :)

Oh, ok, will try to send proper patch, once I figure out what to write in the changelog :)