On Thu, 2016-08-18 at 17:39 +0300, Alexey Dobriyan wrote:
> FYI,
>
> on x86_64, ->anon_vma_chain has offset 120 inside the structure
> which means that:
> * on CONFIG_NUMA=n CONFIG_USERFAULTFD=n kernels
> every 4-th VMA has this list head spanning 2 cachelines and,
>
> * on CONFIG_NUMA=y CONFIG_USERFAULTFD=y kernels
> _every_ VMA has this peculiar property.
It may make sense to move vm_pgoff into the first
cache line, since that is likely to be used in
conjunction with the rb tree, in rb tree walks.
> Now I don't know good benchmark for anon vmas,
> but maybe you do.
I am not sure what we would use to benchmark this.
> struct vm_area_struct {
> vm_start; /* 0 8 */
> vm_end; /* 8 8 */
> vm_next; /* 16 8 */
> vm_prev; /* 24 8 */
> vm_rb; /* 32 24 */
> rb_subtree_gap; /* 56 8 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> vm_mm; /* 64 8 */
> vm_page_prot; /* 72 8 */
> vm_flags; /* 80 8 */
>
> rb; /* 88 24 */
> rb_subtree_last; /* 112 8 */
> /* 88 32 */
>
>
> ===> struct list_head anon_vma_chain; /* 120 16 */
> /* --- cacheline 2 boundary (128 bytes) was 8 bytes ago ---
> */
>
>
> anon_vma; /* 136 8 */
> struct * vm_ops; /* 144 8 */
> vm_pgoff; /* 152 8 */
> vm_file; /* 160 8 */
> vm_private_data; /* 168 8 */
> vm_userfaultfd_ctx; /* 176 0 */
>
> /* size: 176, cachelines: 3, members: 17 */
> /* last cacheline: 48 bytes */
> };
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