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.
Now I don't know good benchmark for anon vmas,
but maybe you do.
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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