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

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Date:   Mon, 23 Jan 2017 16:13:39 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        zhouxianrong <zhouxianrong@...wei.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 15:27), Joonsoo Kim wrote:
> Hello,
> 
> Think about following case in 64 bits kernel.
> 
> If value pattern in the page is like as following, we cannot detect
> the same page with 'unsigned int' element.
> 
> AAAAAAAABBBBBBBBAAAAAAAABBBBBBBB...
> 
> 4 bytes is 0xAAAAAAAA and next 4 bytes is 0xBBBBBBBB and so on.

yep, that's exactly the case that I though would be broken
with a 4-bytes pattern matching. so my conlusion was that
for 4 byte pattern we would have working detection anyway,
for 8 bytes patterns we might have some extra matching.
not sure if it matters that much though.

	-ss