linux-kernel - Re: [PATCH v3 9/9] zram: use crypto decompress

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Date:	Fri, 25 Sep 2015 14:46:47 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH v3 9/9] zram: use crypto decompress_noctx API

On Mon, Sep 21, 2015 at 12:51:28PM +0900, Minchan Kim wrote:
> On Fri, Sep 18, 2015 at 02:19:24PM +0900, Joonsoo Kim wrote:
> > Crypto subsystem now supports decompress_noctx API that requires
> > special tfm_noctx. This tfm can be shared by multiple concurrent
> > decompress user because this API doesn't rely on this tfm object
> > except to fetch decompress function pointer.
> > 
> > Until changing to use crypto API, zram doesn't require any zstrm
> > on decompress so decompress is parallelized unlimitedly. But, previous
> > patch make zram to use crypto API and this requires one zstrm on every
> > decompress users so, in some zstrm contended situations, zram's
> > performance would be degraded.
> > 
> > This patch makes zram use decompress_noctx API and restore zram's
> > performance as the time that zram doesn't use crypto API.
> > 
> > Following is zram's read performance number.
> > 
> > * iozone -t 4 -R -r 16K -s 60M -I +Z -i 0 -i 1
> > * max_stream is set to 1
> > * Output is in Kbytes/sec
> > 
> > zram-base vs zram-crypto vs zram-crypto-noctx
> > 
> > Read		10411701.88	6426911.62	9423894.38
> > Re-read		10017386.62	6428218.88	11000063.50
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  drivers/block/zram/zcomp.c | 24 +++++++++++++++++++++++-
> >  drivers/block/zram/zcomp.h |  1 +
> >  2 files changed, 24 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index c2ed7c8..a020200 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -319,9 +319,12 @@ void zcomp_compress_end(struct zcomp *comp, struct zcomp_strm *zstrm)
> >  	zcomp_strm_release(comp, zstrm);
> >  }
> >  
> > -/* Never return NULL, may sleep */
> > +/* May return NULL, may sleep */
> >  struct zcomp_strm *zcomp_decompress_begin(struct zcomp *comp)
> >  {
> > +	if (comp->tfm_noctx)
> > +		return NULL;
> 
> Hmm,, I understand why returns NULL but it seems to be awkward to use NULL
> to express meaningful semantic and following functions relies on.
> If I have a time, I will think over.

I also think that it's not good thing but I can't think any better
idea. Please let me know if you have better one.

> 
> > +
> >  	return zcomp_strm_find(comp);
> >  }
> >  
> > @@ -346,11 +349,18 @@ int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
> >  {
> >  	unsigned int size = PAGE_SIZE;
> >  
> > +	if (!zstrm) {
> > +		return crypto_comp_decompress_noctx(comp->tfm_noctx,
> > +						src, src_len, dst, &size);
> > +	}
> > +
> >  	return crypto_comp_decompress(zstrm->tfm, src, src_len,	dst, &size);
> >  }
> >  
> >  void zcomp_destroy(struct zcomp *comp)
> >  {
> > +	if (comp->tfm_noctx)
> > +		crypto_free_comp_noctx(comp->tfm_noctx);
> >  	comp->destroy(comp);
> >  	kfree(comp);
> >  }
> > @@ -366,6 +376,7 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> >  {
> >  	struct zcomp *comp;
> >  	const char *backend;
> > +	struct crypto_comp *tfm;
> >  
> >  	backend = find_backend(compress);
> >  	if (!backend)
> > @@ -384,5 +395,16 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> >  		kfree(comp);
> >  		return ERR_PTR(-ENOMEM);
> >  	}
> > +
> > +	/*
> > +	 * Prepare to use crypto decompress_noctx API. One tfm is required
> > +	 * to initialize crypto algorithm properly and fetch corresponding
> > +	 * function pointer. But, it is sharable for multiple concurrent
> > +	 * decompress users.
> > +	 */
> 
> Please comment out that this API will return NULL if the compressor doesn't
> support noctx mode.

Will do.

Thanks.
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