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Thu, 8 May 2025 14:19:57 +0000 (GMT) Message-ID: <6046d139-2a46-4824-bdfc-687750c1ee5b@linux.ibm.com> Date: Thu, 8 May 2025 16:19:55 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv7 10/24] zram: add zlib compression backend support To: Sergey Senozhatsky Cc: Minchan Kim , linux-kernel@vger.kernel.org, Andrew Morton , Ilya Leoshkevich , Heiko Carstens , linux-s390@vger.kernel.org References: <20240902105656.1383858-1-senozhatsky@chromium.org> <20240902105656.1383858-11-senozhatsky@chromium.org> Content-Language: en-US From: Zaslonko Mikhail In-Reply-To: <20240902105656.1383858-11-senozhatsky@chromium.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTA4MDEyMCBTYWx0ZWRfX7qBZo6asl6pf nasu5CtQ/I3nGuBpw4+0+8DD0dv/O5TGlM5VdB/a5UGJB2+BtwjLOvmKXhNePYIYjegfWujqUbs 2BBaUPKt4gy1UCT3NRY2JsBI6pycxIjna3jOM5pbSw3FPxFE3/pdTvL45XF9S4t6k3QaIojFX3W vqaKyfbihntn1JlfAwN4MggBKIlkX4SxvayT5UwMA1i8YeLmS5zQXqX5SrRRXZ+1MMfuV9UomSK Fl7z8Gy2/6z7RBM1GOn/cqlNQOCLkNYTi8wN6AxIDmKOtbOB4xwrRrJG6dx91rMCmAC/oe94ejX 2umkYoOdhs6uynkqqN3hLJ3SfYdxUIEEfXIr+sn6lvFyFhWFhazzkXiLnWR2c7bUolE1ktIU/aW sKj7VLVszDdQ12c+RMUlT9FPFOqx3d3jCO7zhb8Amd4f+LyOkh5k2XSpR4exTEx32IIQonYF X-Authority-Analysis: v=2.4 cv=RIGzH5i+ c=1 sm=1 tr=0 ts=681cbd91 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=cm27Pg_UAAAA:8 a=EwjiY0pQsr8U1XeyRU0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: 8dzpQ9hiECxgtoxRz0_p9h_in7PeFIRc X-Proofpoint-ORIG-GUID: 8dzpQ9hiECxgtoxRz0_p9h_in7PeFIRc X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-08_05,2025-05-07_02,2025-02-21_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 clxscore=1011 bulkscore=0 mlxscore=0 phishscore=0 mlxlogscore=999 malwarescore=0 impostorscore=0 spamscore=0 lowpriorityscore=0 adultscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2504070000 definitions=main-2505080120 Hello Sergey, On 02.09.2024 12:55, Sergey Senozhatsky wrote: > Add s/w zlib (inflate/deflate) compression. > > Signed-off-by: Sergey Senozhatsky > --- > diff --git a/drivers/block/zram/backend_deflate.c b/drivers/block/zram/backend_deflate.c > new file mode 100644 > index 000000000000..acefb86701b9 > --- /dev/null > +++ b/drivers/block/zram/backend_deflate.c > @@ -0,0 +1,132 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > + > +#include > +#include > +#include > +#include > + > +#include "backend_deflate.h" > + > +/* Use the same value as crypto API */ > +#define DEFLATE_DEF_WINBITS 11 > +#define DEFLATE_DEF_MEMLEVEL MAX_MEM_LEVEL > + I was trying to use a zram device with a deflate compression algorithm tuned for s390 hardware acceleration. While I was able to set the compression level via algorithm_params sysfs attribute, I figured out that the window size used by zram zlib compression is limited to 4K since windowBits parameter is hardcoded to DEFLATE_DEF_WINBITS. In order to utilize s390 hardware deflate acceleration, the maximum window size is needed (windowBits of 15), which is also a zlib default. Thus, I'm wondering why windowBits value of 11 was picked for zram zlib compression backend support. The comment line says 'Use the same value as crypto API'... could you please clarify here? Are there some memory constraints? I tried to build the kernel with DEFLATE_DEF_WINBITS set to 15 and verified that s390 hardware deflate acceleration works for zram devices with a deflate compression. Thanks, Mikhail