Re: [PATCH v3 9/9] zram: use crypto decompress_noctx API

[Minchan Kim <minchan@kernel.org>]

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@lge.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.

> +
>  	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.

Thanks.