From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>,
Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Nitin Gupta <ngupta@vflare.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv3 5/8] documentation: Add recompression documentation
Date: Tue, 18 Oct 2022 11:50:21 +0900 [thread overview]
Message-ID: <Y04UbTZh3fJYPhvJ@google.com> (raw)
In-Reply-To: <20221009090720.1040633-6-senozhatsky@chromium.org>
Document user-space visible device attributes that
are enabled by ZRAM_MULTI_COMP.
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
Documentation/admin-guide/blockdev/zram.rst | 55 +++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index c73b16930449..f09e778bc3dc 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -401,6 +401,61 @@ budget in next setting is user's job.
If admin wants to measure writeback count in a certain period, they could
know it via /sys/block/zram0/bd_stat's 3rd column.
+recompression
+-------------
+
+With CONFIG_ZRAM_MULTI_COMP, zram can recompress idle/huge pages using
+alternative (secondary) compression algorithm. The basic idea is that
+alternative compression algorithm can provide better compression ratio
+at a price of (potentially) slower compression/decompression speeds.
+Alternative compression algorithm can, for example, be more successful
+compressing huge pages (those that default algorithm failed to compress).
+Another application is idle pages recompression - pages that are cold and
+sit in the memory can be recompressed using more effective algorithm and,
+hence, reduce zsmalloc memory usage.
+
+With CONFIG_ZRAM_MULTI_COMP, zram will setup two compression algorithms
+per-CPU: primary and secondary ones. Primary zram compressor is explained
+in "3) Select compression algorithm", the secondary algorithm is configured
+in a similar way, using recomp_algorithm device attribute:
+
+Examples::
+
+ #show supported recompression algorithms
+ cat /sys/block/zramX/recomp_algorithm
+ zstd [lzo]
+
+ #select zstd recompression algorithm
+ echo zstd > /sys/block/zramX/recomp_algorithm
+
+Another device attribute that CONFIG_ZRAM_MULTI_COMP enables is recompress,
+which controls recompression:
+
+Examples::
+
+ #IDLE pages recompression is activated by `idle` mode
+ echo idle > /sys/block/zramX/recompress
+
+ #HUGE pages recompression is activated by `huge` mode
+ echo huge > /sys/block/zram0/recompress
+
+ #HUGE_IDLE pages recompression is activated by `huge_idle` mode
+ echo huge_idle > /sys/block/zramX/recompress
+
+The number of idle pages can be significant, so user-space can pass a size
+watermark (in bytes) value to the recompress knob, to filter out idle pages
+for recompression: zram will recompress only idle pages of equal or greater
+size (bytes):::
+
+ #recompress idle pages larger than 3000 bytes
+ echo 3000 > /sys/block/zramX/recompress
+
+ #recompress idle pages larger than 2000 bytes
+ echo 2000 > /sys/block/zramX/recompress
+
+Recompression is mostly focused on idle pages (except for huge pages
+recompression), so it works better in conjunction with memory tracking.
+
memory tracking
===============
--
2.38.0.413.g74048e4d9e-goog
next prev parent reply other threads:[~2022-10-18 2:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-09 9:07 [PATCHv3 0/8] zram: Support multiple compression streams Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 1/8] zram: Preparation for multi-zcomp support Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 2/8] zram: Add recompression algorithm sysfs knob Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 3/8] zram: Factor out WB and non-WB zram read functions Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 4/8] zram: Introduce recompress sysfs knob Sergey Senozhatsky
2022-10-18 0:08 ` Andrew Morton
2022-10-18 2:12 ` Sergey Senozhatsky
2022-10-18 2:42 ` Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 5/8] documentation: Add recompression documentation Sergey Senozhatsky
2022-10-18 2:22 ` Sergey Senozhatsky
2022-10-18 3:11 ` Andrew Morton
2022-10-18 2:50 ` Sergey Senozhatsky [this message]
2022-10-09 9:07 ` [PATCHv3 6/8] zram: Add recompression algorithm choice to Kconfig Sergey Senozhatsky
2022-10-18 3:07 ` Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 7/8] zram: Add recompress flag to read_block_state() Sergey Senozhatsky
2022-10-09 9:07 ` [PATCHv3 8/8] zram: correct typos Sergey Senozhatsky
2022-10-18 0:08 ` Andrew Morton
2022-10-18 2:10 ` Sergey Senozhatsky
2022-10-18 3:11 ` [PATCHv3 0/8] zram: Support multiple compression streams Sergey Senozhatsky
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