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

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Date:   Mon, 23 Jan 2017 13:03:47 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     zhouxianrong <zhouxianrong@...wei.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, sergey.senozhatsky@...il.com,
        minchan@...nel.org, ngupta@...are.org, Mi.Sophia.Wang@...wei.com,
        zhouxiyu@...wei.com, weidu.du@...wei.com, zhangshiming5@...wei.com,
        won.ho.park@...wei.com
Subject: Re: [PATCH] mm: extend zero pages to same element pages for zram

On (01/23/17 11:58), Joonsoo Kim wrote:
> Hello,
> 
> On Sun, Jan 22, 2017 at 10:58:38AM +0800, zhouxianrong wrote:
> > 1. memset is just set a int value but i want to set a long value.
> 
> Sorry for late review.
> 
> Do we really need to set a long value? I cannot believe that
> long value is repeated in the page. Value repeatition is
> usually done by value 0 or 1 and it's enough to use int. And, I heard
> that value 0 or 1 is repeated in Android. Could you check the distribution
> of the value in the same page?

Hello Joonsoo,

thanks for taking a look and for bringing this question up.
so I kinda wanted to propose union of `ulong handle' with `uint element'
and switching to memset(), but I couldn't figure out if that change would
break detection of some patterns.

 /* Allocated for each disk page */
 struct zram_table_entry {
-       unsigned long handle;
+       union {
+               unsigned long handle;
+               unsigned int element;
+       };
        unsigned long value;
 };

	-ss