mm: move lesser used vma_area_struct members into the last cacheline

mm: move lesser used vma_area_struct members into the last cacheline

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 : ...

Link: https://lkml.kernel.org/r/20250213224655.1680278-14-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>