From 783784582225e8ddfbf07993d9fc278bf08025c5 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Thu, 3 Jun 2021 13:37:45 -0700 Subject: [PATCH] Linux: Set spl_kmem_cache_slab_limit when page size !4K For small objects the kernel's slab implementation is very fast and space efficient. However, as the allocation size increases to require multiple pages performance suffers. The SPL kmem cache allocator was designed to better handle these large allocation sizes. Therefore, on Linux the kmem_cache_* compatibility wrappers prefer to use the kernel's slab allocator for small objects and the custom SPL kmem cache allocator for larger objects. This logic was effectively disabled for all architectures using a non-4K page size which caused all kmem caches to only use the SPL implementation. Functionally this is fine, but the SPL code which calculates the target number of objects per-slab does not take in to account that __vmalloc() always returns page-aligned memory. This can result in a massive amount of wasted space when allocating tiny objects on a platform using large pages (64k). To resolve this issue we set the spl_kmem_cache_slab_limit cutoff to 16K for all architectures. This particular change does not attempt to update the logic used to calculate the optimal number of pages per slab. This remains an issue which should be addressed in a future change. Reviewed-by: Matthew Ahrens Reviewed-by: Tony Nguyen Signed-off-by: Brian Behlendorf Closes #12152 Closes #11429 Closes #11574 Closes #12150 --- module/os/linux/spl/spl-kmem-cache.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/module/os/linux/spl/spl-kmem-cache.c b/module/os/linux/spl/spl-kmem-cache.c index 3699b6a159a1..2151ef008fd6 100644 --- a/module/os/linux/spl/spl-kmem-cache.c +++ b/module/os/linux/spl/spl-kmem-cache.c @@ -100,13 +100,10 @@ MODULE_PARM_DESC(spl_kmem_cache_max_size, "Maximum size of slab in MB"); * For small objects the Linux slab allocator should be used to make the most * efficient use of the memory. However, large objects are not supported by * the Linux slab and therefore the SPL implementation is preferred. A cutoff - * of 16K was determined to be optimal for architectures using 4K pages. + * of 16K was determined to be optimal for architectures using 4K pages and + * to also work well on architecutres using larger 64K page sizes. */ -#if PAGE_SIZE == 4096 unsigned int spl_kmem_cache_slab_limit = 16384; -#else -unsigned int spl_kmem_cache_slab_limit = 0; -#endif module_param(spl_kmem_cache_slab_limit, uint, 0644); MODULE_PARM_DESC(spl_kmem_cache_slab_limit, "Objects less than N bytes use the Linux slab");