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

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Message-ID: <20170113070245.GB484@jagdpanzerIV.localdomain>
Date:   Fri, 13 Jan 2017 16:02:45 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        zhouxianrong@...wei.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        sergey.senozhatsky@...il.com, 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 (01/13/17 15:47), Minchan Kim wrote:
[..]
> > > Could you elaborate a bit? Do you mean this?
> > > 
> > >         ret = scnprintf(buf, PAGE_SIZE,
> > >                         "%8llu %8llu %8llu %8lu %8ld %8llu %8lu\n",
> > >                         orig_size << PAGE_SHIFT,
> > >                         (u64)atomic64_read(&zram->stats.compr_data_size),
> > >                         mem_used << PAGE_SHIFT,
> > >                         zram->limit_pages << PAGE_SHIFT,
> > >                         max_used << PAGE_SHIFT,
> > >                         // (u64)atomic64_read(&zram->stats.zero_pages),
> > >                         (u64)atomic64_read(&zram->stats.same_pages),
> > >                         pool_stats.pages_compacted);
> > 
> > yes, correct.
> > 
> > do we need to export it as two different stats (zero_pages and
> > same_pages), if those are basically same thing internally?
> 
> So, let summary up.
> 
> 1. replace zero_page stat into same page stat in mm_stat
> 2. s/zero_pages/same_pages/Documentation/blockdev/zram.txt
> 3. No need to warn to "cat /sys/block/zram0/mm_stat" user to see zero_pages
>    about semantic change

1) account zero_page and same_pages in one attr.

	this already is in the patch.

2) do not rename zero_pages attr.

	we can't do this so fast, I think.


> 3. No need to warn to "cat /sys/block/zram0/mm_stat" user to see zero_pages
>    about semantic change

yes. we just _may_ have more pages (depending on data pattern) which we treat
as "zero" pages internally. this results in lower memory consumption. I don't
think warn users about this change is necessary; they won't be able to do
anything about it anyway. zero_pages stat is pretty much just a fun number to
know. isn't it?

or do you think that we should account it in separate stats?

	-ss