linux-kernel - Re: [PATCH v3] zram: extend zero pages to same element pages

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Date:   Mon, 23 Jan 2017 16:45:42 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     zhouxianrong <zhouxianrong@...wei.com>
Cc:     Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, Mi.Sophia.Wang@...wei.com,
        zhouxiyu@...wei.com, weidu.du@...wei.com, zhangshiming5@...wei.com,
        won.ho.park@...wei.com
Subject: Re: [PATCH v3] zram: extend zero pages to same element pages

On Mon, Jan 23, 2017 at 02:17:23PM +0800, zhouxianrong wrote:
> i am not sure as well about reverse hurting cache.
> 
> On 2017/1/23 14:13, Joonsoo Kim wrote:
> >On Mon, Jan 23, 2017 at 01:47:20PM +0900, Minchan Kim wrote:
> >>Hello,
> >>
> >>When I look at first patch, I wanted to use increment loop but didn't
> >>tell to you because that small piece of code is no harmful for readbility
> >>to me so I want to keep author's code rather than pointing the trivial
> >>which is just matter of preference out.
> >>
> >>Rather than readiblity, I suspect it might hurt performance and talked
> >>with Namhyung but we cannot find anything decremental loop is bad
> >>compared to incremental. Rather than, many articles have been said
> >>decrement loop is faster like zhouxianrong's mentiond although I don't
> >>think it makes marginal difference.
> >>
> >>Joonsoo, why do you think incremental is faster?
> >>zhouxianrong, why do you think decrement loops makes cache problem?
> >>
> >>I'm okay either way. Just want to know why you guys think about it.
> >
> >Hmm... I guess that cache prefetcher works better for forward access
> >but I'm not sure.
 
If there is no one to ask changing it to incremental, I wanted to go
with decremental you wrote firstly but now there is one more people
who likes incremental loop as well as me. And he spent a time to his
precious time for review so we should take care of his credit.

So, please go with incremental approach if you are not against.
Please resend the patch by yourself. With patch I sent today, I guess
you got to know my intention about semantic change of documentation
, description change to notice zero page change risk and remoe
partial handling function. :)

Thanks.