linux-kernel - Re: [PATCH] zram: introduce per-device debug

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Date:	Fri, 13 May 2016 10:09:29 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] zram: introduce per-device debug_stat sysfs node

Hello Minchan,

On (05/13/16 08:41), Minchan Kim wrote:
[..]

will fix and update, thanks!

> > @@ -719,6 +737,8 @@ compress_again:
> >  		zcomp_strm_release(zram->comp, zstrm);
> >  		zstrm = NULL;
> >  
> > +		atomic64_inc(&zram->stats.num_recompress);
> > +
> 
> It should be below "goto compress_again".

I moved it out of goto intentionally. this second zs_malloc()

		handle = zs_malloc(meta->mem_pool, clen,
				GFP_NOIO | __GFP_HIGHMEM |
				__GFP_MOVABLE);

can take some time to complete, which will slow down zram for a bit,
and _theoretically_ this second zs_malloc() still can fail. yes, we
would do the error print out pr_err("Error allocating memory ... ")
and inc the `failed_writes' in zram_bvec_rw(), but zram_bvec_write()
has several more error return paths that can inc the `failed_writes'.
so by just looking at the stats we won't be able to tell that we had
failed fast path allocation combined with failed slow path allocation
(IOW, `goto recompress' never happened).

so I'm thinking about changing its name to num_failed_fast_compress
or num_failed_fast_write, or something similar and thus count the number
of times we fell to "!handle" branch, not the number of goto-s.
what do you think? or do you want it to be num_recompress specifically?

> Other than that,
> 
> Acked-by: Minchan Kim <minchan@...nel.org>
> 

thanks.

	-ss