From 514d661ca1d5df1f5e4f852d169f6969fcff2994 Mon Sep 17 00:00:00 2001 From: Alexander Motin Date: Mon, 30 Oct 2023 17:55:32 -0400 Subject: [PATCH] Tune zio buffer caches and their alignments We should not always use PAGESIZE alignment for caches bigger than it and SPA_MINBLOCKSIZE otherwise. Doing that caches for 5, 6, 7, 10 and 14KB rounded up to 8, 12 and 16KB respectively make no sense. Instead specify as alignment the biggest power-of-2 divisor. This way 2KB and 6KB caches are both aligned to 2KB, while 4KB and 8KB are aligned to 4KB. Reduce number of caches to half-power of 2 instead of quarter-power of 2. This removes caches difficult for underlying allocators to fit into page-granular slabs, such as: 2.5, 3.5, 5, 7, 10KB, etc. Since these caches are mostly used for transient allocations like ZIOs and small DBUF cache it does not worth being too aggressive. Due to the above alignment issue some of those caches were not working properly any way. 6KB cache now finally has a chance to work right, placing 2 buffers into 3 pages, that makes sense. Remove explicit alignment in Linux user-space case. I don't think it should be needed any more with the above fixes. As result on FreeBSD instead of such numbers of pages per slab: vm.uma.zio_buf_comb_16384.keg.ppera: 4 vm.uma.zio_buf_comb_14336.keg.ppera: 4 vm.uma.zio_buf_comb_12288.keg.ppera: 3 vm.uma.zio_buf_comb_10240.keg.ppera: 3 vm.uma.zio_buf_comb_8192.keg.ppera: 2 vm.uma.zio_buf_comb_7168.keg.ppera: 2 vm.uma.zio_buf_comb_6144.keg.ppera: 2 <= Broken vm.uma.zio_buf_comb_5120.keg.ppera: 2 vm.uma.zio_buf_comb_4096.keg.ppera: 1 vm.uma.zio_buf_comb_3584.keg.ppera: 7 <= Hard to free vm.uma.zio_buf_comb_3072.keg.ppera: 3 vm.uma.zio_buf_comb_2560.keg.ppera: 2 vm.uma.zio_buf_comb_2048.keg.ppera: 1 vm.uma.zio_buf_comb_1536.keg.ppera: 2 vm.uma.zio_buf_comb_1024.keg.ppera: 1 vm.uma.zio_buf_comb_512.keg.ppera: 1 I am now getting such: vm.uma.zio_buf_comb_16384.keg.ppera: 4 vm.uma.zio_buf_comb_12288.keg.ppera: 3 vm.uma.zio_buf_comb_8192.keg.ppera: 2 vm.uma.zio_buf_comb_6144.keg.ppera: 3 <= Fixed, 2 in 3 pages vm.uma.zio_buf_comb_4096.keg.ppera: 1 vm.uma.zio_buf_comb_3072.keg.ppera: 3 vm.uma.zio_buf_comb_2048.keg.ppera: 1 vm.uma.zio_buf_comb_1536.keg.ppera: 2 vm.uma.zio_buf_comb_1024.keg.ppera: 1 vm.uma.zio_buf_comb_512.keg.ppera: 1 Reviewed-by: Allan Jude Reviewed-by: Brian Behlendorf Signed-off-by: Alexander Motin Sponsored by: iXsystems, Inc. Closes #15452 --- module/zfs/zio.c | 87 +++++++++++++++++++++--------------------------- 1 file changed, 38 insertions(+), 49 deletions(-) diff --git a/module/zfs/zio.c b/module/zfs/zio.c index 3eb472a9f..4eb276352 100644 --- a/module/zfs/zio.c +++ b/module/zfs/zio.c @@ -158,23 +158,22 @@ zio_init(void) zio_link_cache = kmem_cache_create("zio_link_cache", sizeof (zio_link_t), 0, NULL, NULL, NULL, NULL, NULL, 0); - /* - * For small buffers, we want a cache for each multiple of - * SPA_MINBLOCKSIZE. For larger buffers, we want a cache - * for each quarter-power of 2. - */ for (c = 0; c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; c++) { size_t size = (c + 1) << SPA_MINBLOCKSHIFT; + size_t align, cflags, data_cflags; + char name[32]; + + /* + * Create cache for each half-power of 2 size, starting from + * SPA_MINBLOCKSIZE. It should give us memory space efficiency + * of ~7/8, sufficient for transient allocations mostly using + * these caches. + */ size_t p2 = size; - size_t align = 0; - size_t data_cflags, cflags; - - data_cflags = KMC_NODEBUG; - cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ? - KMC_NODEBUG : 0; - while (!ISP2(p2)) p2 &= p2 - 1; + if (!IS_P2ALIGNED(size, p2 / 2)) + continue; #ifndef _KERNEL /* @@ -185,47 +184,37 @@ zio_init(void) */ if (arc_watch && !IS_P2ALIGNED(size, PAGESIZE)) continue; - /* - * Here's the problem - on 4K native devices in userland on - * Linux using O_DIRECT, buffers must be 4K aligned or I/O - * will fail with EINVAL, causing zdb (and others) to coredump. - * Since userland probably doesn't need optimized buffer caches, - * we just force 4K alignment on everything. - */ - align = 8 * SPA_MINBLOCKSIZE; -#else - if (size < PAGESIZE) { - align = SPA_MINBLOCKSIZE; - } else if (IS_P2ALIGNED(size, p2 >> 2)) { - align = PAGESIZE; - } #endif - if (align != 0) { - char name[36]; - if (cflags == data_cflags) { - /* - * Resulting kmem caches would be identical. - * Save memory by creating only one. - */ - (void) snprintf(name, sizeof (name), - "zio_buf_comb_%lu", (ulong_t)size); - zio_buf_cache[c] = kmem_cache_create(name, - size, align, NULL, NULL, NULL, NULL, NULL, - cflags); - zio_data_buf_cache[c] = zio_buf_cache[c]; - continue; - } - (void) snprintf(name, sizeof (name), "zio_buf_%lu", - (ulong_t)size); - zio_buf_cache[c] = kmem_cache_create(name, size, - align, NULL, NULL, NULL, NULL, NULL, cflags); + if (IS_P2ALIGNED(size, PAGESIZE)) + align = PAGESIZE; + else + align = 1 << (highbit64(size ^ (size - 1)) - 1); - (void) snprintf(name, sizeof (name), "zio_data_buf_%lu", - (ulong_t)size); - zio_data_buf_cache[c] = kmem_cache_create(name, size, - align, NULL, NULL, NULL, NULL, NULL, data_cflags); + cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ? + KMC_NODEBUG : 0; + data_cflags = KMC_NODEBUG; + if (cflags == data_cflags) { + /* + * Resulting kmem caches would be identical. + * Save memory by creating only one. + */ + (void) snprintf(name, sizeof (name), + "zio_buf_comb_%lu", (ulong_t)size); + zio_buf_cache[c] = kmem_cache_create(name, size, align, + NULL, NULL, NULL, NULL, NULL, cflags); + zio_data_buf_cache[c] = zio_buf_cache[c]; + continue; } + (void) snprintf(name, sizeof (name), "zio_buf_%lu", + (ulong_t)size); + zio_buf_cache[c] = kmem_cache_create(name, size, align, + NULL, NULL, NULL, NULL, NULL, cflags); + + (void) snprintf(name, sizeof (name), "zio_data_buf_%lu", + (ulong_t)size); + zio_data_buf_cache[c] = kmem_cache_create(name, size, align, + NULL, NULL, NULL, NULL, NULL, data_cflags); } while (--c != 0) {