Re: [PATCH 13/35] autonuma: add page structure fields

KOSAKI Motohiro
2012-05-30T08:25:38Z

(5/29/12 10:54 AM), Peter Zijlstra wrote:
> On Tue, 2012-05-29 at 09:56 -0400, Rik van Riel wrote:
>> On 05/29/2012 09:16 AM, Peter Zijlstra wrote:
>>> On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
>>
>>> 24 bytes per page.. or ~0.6% of memory gone. This is far too great a
>>> price to pay.
>>>
>>> At LSF/MM Rik already suggested you limit the number of pages that can
>>> be migrated concurrently and use this to move the extra list_head out of
>>> struct page and into a smaller amount of extra structures, reducing the
>>> total overhead.
>>
>> For THP, we should be able to track this NUMA info on a
>> 2MB page granularity.
>
> Yeah, but that's another x86-only feature, _IF_ we're going to do this
> it must be done for all archs that have CONFIG_NUMA, thus we're stuck
> with 4k (or other base page size).

Even if THP=n, we don't need 4k granularity. All modern malloc implementation have
per-thread heap (e.g. glibc call it as arena) and it is usually 1-8MB size. So, if
it is larger than 2MB, we can always use per-pmd tracking. iow, memory consumption
reduce to 1/512.

My suggestion is, track per-pmd (i.e. 2M size) granularity and fix glibc too (current
glibc malloc has dynamically arena size adjusting feature and then it often become
less than 2M).