Re: [PATCH v10 13/18] mm: move lesser used vma_area_struct members into the last cacheline

[Vlastimil Babka <vbabka@suse.cz>]

On 2/13/25 23:46, Suren Baghdasaryan wrote:
> Move several vma_area_struct members which are rarely or never used
> during page fault handling into the last cacheline to better pack
> vm_area_struct. As a result vm_area_struct will fit into 3 as opposed
> to 4 cachelines. New typical vm_area_struct layout:
> 
> struct vm_area_struct {
>     union {
>         struct {
>             long unsigned int vm_start;              /*     0     8 */
>             long unsigned int vm_end;                /*     8     8 */
>         };                                           /*     0    16 */
>         freeptr_t          vm_freeptr;               /*     0     8 */
>     };                                               /*     0    16 */
>     struct mm_struct *         vm_mm;                /*    16     8 */
>     pgprot_t                   vm_page_prot;         /*    24     8 */
>     union {
>         const vm_flags_t   vm_flags;                 /*    32     8 */
>         vm_flags_t         __vm_flags;               /*    32     8 */
>     };                                               /*    32     8 */
>     unsigned int               vm_lock_seq;          /*    40     4 */
> 
>     /* XXX 4 bytes hole, try to pack */
> 
>     struct list_head           anon_vma_chain;       /*    48    16 */
>     /* --- cacheline 1 boundary (64 bytes) --- */
>     struct anon_vma *          anon_vma;             /*    64     8 */
>     const struct vm_operations_struct  * vm_ops;     /*    72     8 */
>     long unsigned int          vm_pgoff;             /*    80     8 */
>     struct file *              vm_file;              /*    88     8 */
>     void *                     vm_private_data;      /*    96     8 */
>     atomic_long_t              swap_readahead_info;  /*   104     8 */
>     struct mempolicy *         vm_policy;            /*   112     8 */
>     struct vma_numab_state *   numab_state;          /*   120     8 */
>     /* --- cacheline 2 boundary (128 bytes) --- */
>     refcount_t          vm_refcnt (__aligned__(64)); /*   128     4 */
> 
>     /* XXX 4 bytes hole, try to pack */
> 
>     struct {
>         struct rb_node     rb (__aligned__(8));      /*   136    24 */
>         long unsigned int  rb_subtree_last;          /*   160     8 */
>     } __attribute__((__aligned__(8))) shared;        /*   136    32 */
>     struct anon_vma_name *     anon_name;            /*   168     8 */
>     struct vm_userfaultfd_ctx  vm_userfaultfd_ctx;   /*   176     8 */
> 
>     /* size: 192, cachelines: 3, members: 18 */
>     /* sum members: 176, holes: 2, sum holes: 8 */
>     /* padding: 8 */
>     /* forced alignments: 2, forced holes: 1, sum forced holes: 4 */
> } __attribute__((__aligned__(64)));
> 
> Memory consumption per 1000 VMAs becomes 48 pages:
> 
>     slabinfo after vm_area_struct changes:
>      <name>           ... <objsize> <objperslab> <pagesperslab> : ...
>      vm_area_struct   ...    192   42    2 : ...
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>