linux-kernel - Re: [RFC] mm: support multi_freearea to the reduction of external fragmentation

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Date:   Thu, 22 Apr 2021 11:37:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "lipeifeng@...o.com" <lipeifeng@...o.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        peifengl55 <peifengl55@...il.com>,
        schwidefsky <schwidefsky@...ibm.com>,
        "heiko.carstens" <heiko.carstens@...ibm.com>
Cc:     linux-s390 <linux-s390@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        zhangshiming <zhangshiming@...o.com>,
        guoweichao <guoweichao@...o.com>,
        zhouhuacai <zhouhuacai@...o.com>
Subject: Re: [RFC] mm: support multi_freearea to the reduction of external
 fragmentation

On 19.04.21 04:37, lipeifeng@...o.com wrote:
> Hi Vlastimil Babka:
> Thank you very much indeed for your advice.
> 
> 
> Hi Vlastimil Babka, schwidefsky,heiko.carstens:
> 
> It is a temporary patch to consult experts:
> Is it possible to merge the optimization idea and the implementation
> method to the baseline?

Well, we cannot really say that :)

History taught that merging large and invasive buddy changes is a 
tedious task, can take a long time, and can fail even after a lot of 
discussions and patch series.

Further, usually there has to be a very compelling reason to merge 
large, invasive buddy changes (read: not only optimize very specific 
scenarios); otherwise there will just push back because the invasive 
changes might introduce additional problems or degrade other special 
cases or even the general case.

Last but not least, there have to be more benchmarks and test cases that 
proof that other workload won't be degraded to a degree that people 
care; as one example, this includes runtime overhead when 
allocating/freeing pages.

What usually works best is improving the code in small steps, doing 
minor adjustments but moving into the desired direction.

-- 
Thanks,

David / dhildenb