Re: isolate_freepages_block(): very high intermittent overhead

[Vlastimil Babka <vbabka@suse.cz>]

On 10/28/2014 09:59 AM, Markus Trippelsdorf wrote:
> On 2014.10.27 at 23:01 +0100, Vlastimil Babka wrote:
>> On 10/27/2014 09:40 PM, Markus Trippelsdorf wrote:
>>> On my v3.18-rc2 kernel isolate_freepages_block() sometimes shows up very
>>> high (>20%) in perf top during the configuration phase of software
>>> builds. It increases build time considerably.
>>>
>>> Unfortunately the issue is not 100% reproducible, because it appears
>>> only intermittently. And the symptoms vanish after a few minutes.
>>
>> Does it happen for long enough so you can capture it by perf record -g ?
>
> It only happens when I use the "Lockless Allocator":
> http://locklessinc.com/downloads/lockless_allocator_src.tgz
>
> I use: LD_PRELOAD=/usr/lib/libllalloc.so.1.3 when building software,
> because it gives me a ~8% speed boost over glibc's malloc.

Hm I see. I'll try to test that.

> Unfortunately, I don't have time to debug this further and have disabled
> "Transparent Hugepage Support" for now.

That's unfortunate indeed. Commit 
e14c720efdd73c6d69cd8d07fa894bcd11fe1973 "mm, compaction: remember 
position within pageblock in free pages scanner" would be the most 
suspicious one here I guess, so testing at least a kernel with this 
patch reverted would be very useful. Simple git revert seems to apply 
cleanly here.

Thanks,
Vlastimil

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