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

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Date:   Fri, 13 Jan 2017 15:47:19 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     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 Fri, Jan 13, 2017 at 03:36:14PM +0900, Sergey Senozhatsky wrote:
> On (01/13/17 15:23), Minchan Kim wrote:
> [..]
> > > > Please add same_pages to tail of the stat
> > > 
> > > sounds ok to me. and yes, can deprecate zero_pages.
> > > 
> > > seems that with that patch the concept of ZRAM_ZERO disappears. both
> > > ZERO and SAME_ELEMENT pages are considered to be the same thing now.
> > 
> > Right.
> > 
> > > which is fine and makes sense to me, I think. and if ->.same_pages will
> > > replace ->.zero_pages in mm_stat() then I'm also OK. yes, we will see
> > > increased number in the last column of mm_stat file, but I don't tend
> > > to see any issues here. Minchan, what do you think?
> > 
> > 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

?