Re: [PATCH 2/2] mm/vmalloc: Use kvmalloc to allocate the table of pages
From: Uladzislau Rezki <urezki@gmail.com>
Date: 2021-03-22 22:37:28
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On Mon, Mar 22, 2021 at 07:38:20PM +0000, Matthew Wilcox (Oracle) wrote:
quoted hunk ↗ jump to hunk
If we're trying to allocate 4MB of memory, the table will be 8KiB in size (1024 pointers * 8 bytes per pointer), which can usually be satisfied by a kmalloc (which is significantly faster). Instead of changing this open-coded implementation, just use kvmalloc(). Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- mm/vmalloc.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 96444d64129a..32b640a84250 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c@@ -2802,13 +2802,8 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, gfp_mask |= __GFP_HIGHMEM; /* Please note that the recursion is strictly bounded. */ - if (array_size > PAGE_SIZE) { - pages = __vmalloc_node(array_size, 1, nested_gfp, node, + pages = kvmalloc_node_caller(array_size, nested_gfp, node, area->caller); - } else { - pages = kmalloc_node(array_size, nested_gfp, node); - } - if (!pages) { free_vm_area(area); return NULL;-- 2.30.2
Makes sense to me. Though i expected a bigger difference: # patch single CPU, 4MB allocation, loops: 1000000 avg: 85293854 usec # default single CPU, 4MB allocation, loops: 1000000 avg: 89275857 usec One question. Should we care much about fragmentation? I mean with the patch, allocations > 2MB will do request to SLAB bigger then PAGE_SIZE. Thanks! -- Vlad Rezki