linux-kernel - Re: [PATCH v2 6/7] zram: add bd

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Message-ID: <20181127020754.GB237537@google.com>
Date:   Tue, 27 Nov 2018 11:07:54 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v2 6/7] zram: add bd_stat statistics

On Mon, Nov 26, 2018 at 12:58:33PM -0800, Andrew Morton wrote:
> On Mon, 26 Nov 2018 17:28:12 +0900 Minchan Kim <minchan@...nel.org> wrote:
> 
> > +File /sys/block/zram<id>/bd_stat
> > +
> > +The stat file represents device's backing device statistics. It consists of
> > +a single line of text and contains the following stats separated by whitespace:
> > + bd_count	size of data written in backing device.
> > +		Unit: pages
> > + bd_reads	the number of reads from backing device
> > +		Unit: pages
> > + bd_writes	the number of writes to backing device
> > +		Unit: pages
> 
> Using `pages' is a bad choice.  And I assume this means that
> writeback_limit is in pages as well, which is worse.
> 
> Page sizes are not constant!  We want userspace which was developed on
> 4k pagesize to work the same on 64k pagesize.
> 
> Arguably, we could require that well-written userspace remember to use
> getpagesize().  However we have traditionally tried to avoid that by
> performing the pagesize normalization within the kernel.

zram works based on page so I used that term but I agree it's rather
vague. If there is no objection, I will use (Unit: 4K) instead of
(Unit: pages).