Hello! This RFC series adds feature which allows fold identical zsmalloc objects into a single one. Based on ZRAM version: https://lore.kernel.org/lkml/Y3w8%2Fq%2FHoSbqamoD@xxxxxxxxxx/t/ Let's imagine that 3 objects with the same content got into zsmalloc: +----------------+ +----------------+ +----------------+ | handle 1 | | handle 2 | | handle 3 | +-------+--------+ +-------+--------+ +--------+-------+ | | | | | | +-------v--------+ +-------v---------+ +--------v-------+ |zsmalloc object| |zsmalloc object | |zsmalloc object| ++--------------++ +-+-------------+-+ ++--------------++ +--------------+ +-------------+ +--------------+ | buffer: "abc"| |buffer: "abc"| | buffer: "abc"| +--------------+ +-------------+ +--------------+ As you can see, the data is duplicated. Fold mechanism saves (after scanning objects) only one zsmalloc object. Here's what happens after the scan and fold: +----------------+ +----------------+ +----------------+ | handle 1 | | handle 2 | | handle 3 | +-------+--------+ +-------+--------+ +--------+-------+ | | | | | | | +--------v---------+ | +-----------> zsmalloc object <-----------+ +--+-------------+-+ +-------------+ |buffer: "abc"| +-------------+ Thus, we reduced the amount of memory occupied by 3 times. This mechanism doesn't affect the perf of the zsmalloc itself in any way (maybe just a little bit on the zs_free() function). In order to describe each such identical object, we (constantly) need sizeof(fold_rbtree_node) bytes. Also, all struct size_class now have new field struct rb_root fold_rbtree. Testing on my system (8GB RAM + 1Gb ZRAM SWAP) showed that at high loads, on average, when calling the fold mechanism, we can save up to 15-20% of the memory usage. This patch series adds a new sysfs node into ZRAM - trigger folding and provides new field in mm_stat. This field shows how many pages freed during folding: $ cat /sys/block/zram0/mm_stat 431452160 332984392 339894272 0 339894272 282 0 51374 51374 0 $ echo 1 > /sys/block/zram0/fold $ cat /sys/block/zram/mm_stat 431452160 270376848 287301504 0 339894272 282 0 51374 51374 6593 Alexey Romanov (5): mm/zsmalloc: use ARRAY_SIZE in isolate_zspage() mm/zsmalloc: get rid of PAGE_MASK mm/zsmalloc: introduce objects folding mechanism zram: add fold sysfs knob zram: add pages_folded to stats Documentation/admin-guide/blockdev/zram.rst | 2 + drivers/block/zram/zram_drv.c | 30 +- include/linux/zsmalloc.h | 4 + mm/Kconfig | 9 + mm/zsmalloc.c | 484 +++++++++++++++++++- 5 files changed, 513 insertions(+), 16 deletions(-) -- 2.38.1
