Maybe move ->anon_vma_chain ?

[Alexey Dobriyan <adobriyan@gmail.com>]

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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