linux-kernel - Re: [PATCH 2/2] zram: support deflate-specific params

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Message-ID: <ystv6cvrdllh64eqkislh47a3bnx5d2lk42ox4eiuuubioin6u@gmt5pwbkwiz3>
Date: Thu, 15 May 2025 12:14:38 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Zaslonko Mikhail <zaslonko@...ux.ibm.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Heiko Carstens <hca@...ux.ibm.com>, 
	Ilya Leoshkevich <iii@...ux.ibm.com>, Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH 2/2] zram: support deflate-specific params

Cc-ing Herbert

On (25/05/14 12:58), Zaslonko Mikhail wrote:
> Looks good to me.
> 
> Just a minor comment. If we intend to use raw deflate only, like we do now (no zlib header or
> trailer for the compressed data), we should probably change deflate.winbits to unsigned and
> pass '-deflate.winbits' to zlib_deflateInit2().

Yeah, so in zram we can use only raw deflate (we decompress only what we
have compressed earlier and the data never leaves the device.)  But in case
of Crypto API I actually don't know, added Herbert to the Cc.

> Also, here is another patch suggestion from my side on top of this one. 
> Let me know what you think.
> 
> ---8<---
> 
> zram: Utilize s390 hardware deflate acceleration for zram
> 
> Utilize s390 hardware deflate acceleration for zram deflate compression
> by default when the facility is available.
> 
> Signed-off-by: Mikhail Zaslonko <zaslonko@...ux.ibm.com>
> 
> diff --git a/drivers/block/zram/backend_deflate.c b/drivers/block/zram/backend_deflate.c
> index b75016e0e654..5bfc57522e3a 100644
> --- a/drivers/block/zram/backend_deflate.c
> +++ b/drivers/block/zram/backend_deflate.c
> @@ -22,10 +22,23 @@ static void deflate_release_params(struct zcomp_params *params)
> 
>  static int deflate_setup_params(struct zcomp_params *params)
>  {
> -       if (params->level == ZCOMP_PARAM_NOT_SET)
> -               params->level = Z_DEFAULT_COMPRESSION;
> -       if (params->deflate.winbits == ZCOMP_PARAM_NOT_SET)
> -               params->deflate.winbits = DEFLATE_DEF_WINBITS;
> +       /*
> +        * In case of s390 zlib hardware support available,
> +        * use maximum window size and level one as default compression
> +        * parameters in order to utilize hardware deflate acceleration.
> +        */
> +       if (params->level == ZCOMP_PARAM_NOT_SET) {
> +               if (zlib_deflate_dfltcc_enabled())
> +                       params->level = Z_BEST_SPEED;
> +               else
> +                       params->level = Z_DEFAULT_COMPRESSION;
> +       }
> +       if (params->deflate.winbits == ZCOMP_PARAM_NOT_SET) {
> +               if (zlib_deflate_dfltcc_enabled())
> +                       params->deflate.winbits = -MAX_WBITS;
> +               else
> +                       params->deflate.winbits = DEFLATE_DEF_WINBITS;
> +       }

I'm not sure if we want this much of s390 specific code in the generic
zram/Crypto API code.  Both of these params can be configured by user-space
via the algorithm_params device attribute.