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

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Date:	Fri, 13 May 2016 17:06:43 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] zram: introduce per-device debug_stat sysfs node

On (05/13/16 16:20), Minchan Kim wrote:
> > > > @@ -737,12 +737,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > > >  		zcomp_strm_release(zram->comp, zstrm);
> > > >  		zstrm = NULL;
> > > >  
> > > > -		atomic64_inc(&zram->stats.num_recompress);
> > > > -
> > > >  		handle = zs_malloc(meta->mem_pool, clen,
> > > >  				GFP_NOIO | __GFP_HIGHMEM);
> > > > -		if (handle)
> > > > +		if (handle) {
> > > > +			atomic64_inc(&zram->stats.num_recompress);
> > > >  			goto compress_again;
> > > > +		}


just a small note:

> Although 2 is smaller, your patch just accounts only direct reclaim but my
> suggestion can count both 1 and 2 so isn't it better?

no, my patch accounts 1) and 2) as well. the only difference is that my
patch accounts second zs_malloc() call _EVEN_ if it has failed and we
jumped to goto err (because we still could have done reclaim). the new
version would account second zs_malloc() _ONLY_ if it has succeeded, and
thus possibly reclaim would not be accounted.


recompress:
	compress
	handle = zs_malloc FAST PATH

	if (!handle) {
		release stream
		handle = zs_malloc SLOW PATH

		<< my patch accounts SLOW PATH here >>

		if (handle) {
			num_recompress++  << NEW version accounts it here, only it was OK >>
			goto recompress;
		}

		goto err;    << SLOW PATH is not accounted if SLOW PATH was unsuccessful
	}


	-ss