From 44f76413496ec343da0d8292ceecdcabe3e6ec16 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Mon, 3 Mar 2025 11:03:23 +0900 Subject: zsmalloc: introduce new object mapping API Current object mapping API is a little cumbersome. First, it's inconsistent, sometimes it returns with page-faults disabled and sometimes with page-faults enabled. Second, and most importantly, it enforces atomicity restrictions on its users. zs_map_object() has to return a liner object address which is not always possible because some objects span multiple physical (non-contiguous) pages. For such objects zsmalloc uses a per-CPU buffer to which object's data is copied before a pointer to that per-CPU buffer is returned back to the caller. This leads to another, final, issue - extra memcpy(). Since the caller gets a pointer to per-CPU buffer it can memcpy() data only to that buffer, and during zs_unmap_object() zsmalloc will memcpy() from that per-CPU buffer to physical pages that object in question spans across. New API splits functions by access mode: - zs_obj_read_begin(handle, local_copy) Returns a pointer to handle memory. For objects that span two physical pages a local_copy buffer is used to store object's data before the address is returned to the caller. Otherwise the object's page is kmap_local mapped directly. - zs_obj_read_end(handle, buf) Unmaps the page if it was kmap_local mapped by zs_obj_read_begin(). - zs_obj_write(handle, buf, len) Copies len-bytes from compression buffer to handle memory (takes care of objects that span two pages). This does not need any additional (e.g. per-CPU) buffers and writes the data directly to zsmalloc pool pages. In terms of performance, on a synthetic and completely reproducible test that allocates fixed number of objects of fixed sizes and iterates over those objects, first mapping in RO then in RW mode: OLD API ======= 3 first results out of 10 369,205,778 instructions # 0.80 insn per cycle 40,467,926 branches # 113.732 M/sec 369,002,122 instructions # 0.62 insn per cycle 40,426,145 branches # 189.361 M/sec 369,036,706 instructions # 0.63 insn per cycle 40,430,860 branches # 204.105 M/sec [..] NEW API ======= 3 first results out of 10 265,799,293 instructions # 0.51 insn per cycle 29,834,567 branches # 170.281 M/sec 265,765,970 instructions # 0.55 insn per cycle 29,829,019 branches # 161.602 M/sec 265,764,702 instructions # 0.51 insn per cycle 29,828,015 branches # 189.677 M/sec [..] T-test on all 10 runs ===================== Difference at 95.0% confidence -1.03219e+08 +/- 55308.7 -27.9705% +/- 0.0149878% (Student's t, pooled s = 58864.4) The old API will stay around until the remaining users switch to the new one. After that we'll also remove zsmalloc per-CPU buffer and CPU hotplug handling. The split of map(RO) and map(WO) into read_{begin/end}/write is suggested by Yosry Ahmed. Link: https://lkml.kernel.org/r/20250303022425.285971-15-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Suggested-by: Yosry Ahmed Reviewed-by: Yosry Ahmed Cc: Hillf Danton Cc: Kairui Song Cc: Minchan Kim Cc: Sebastian Andrzej Siewior Signed-off-by: Andrew Morton --- include/linux/zsmalloc.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include/linux') diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h index a48cd0ffe57d..7d70983cf398 100644 --- a/include/linux/zsmalloc.h +++ b/include/linux/zsmalloc.h @@ -58,4 +58,12 @@ unsigned long zs_compact(struct zs_pool *pool); unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size); void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats); + +void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle, + void *local_copy); +void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, + void *handle_mem); +void zs_obj_write(struct zs_pool *pool, unsigned long handle, + void *handle_mem, size_t mem_len); + #endif -- cgit v1.2.3