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    Subject[PATCH] mm/vmalloc: lock contention optimization under multi-threading
    Date
    When allocating a new memory area where the mapping address range is
    known, it is observed that the vmap_area lock is acquired twice.
    The first acquisition occurs in the alloc_vmap_area() function when
    inserting the vm area into the vm mapping red-black tree. The second
    acquisition occurs in the setup_vmalloc_vm() function when updating the
    properties of the vm, such as flags and address, etc.
    Combine these two operations together in alloc_vmap_area(), which
    improves scalability when the vmap_area lock is contended. By doing so,
    the need to acquire the lock twice can also be eliminated.
    With the above change, tested on intel icelake platform(160 vcpu, kernel
    v6.7), a 6% performance improvement and a 7% reduction in overall
    spinlock hotspot are gained on
    stress-ng/pthread(https://github.com/ColinIanKing/stress-ng), which is
    the stress test of thread creations.

    Reviewed-by: "Chen, Tim C" <tim.c.chen@intel.com>
    Reviewed-by: "King, Colin" <colin.king@intel.com>
    Signed-off-by: rulinhuang <rulin.huang@intel.com>
    ---
    mm/vmalloc.c | 31 +++++++++++++++----------------
    1 file changed, 15 insertions(+), 16 deletions(-)

    diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    index d12a17fc0c171..3b1f616e8ecf0 100644
    --- a/mm/vmalloc.c
    +++ b/mm/vmalloc.c
    @@ -1577,13 +1577,13 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)

    /*
    * Allocate a region of KVA of the specified size and alignment, within the
    - * vstart and vend.
    + * vstart and vend. If vm is passed in, the two will also be bound.
    */
    static struct vmap_area *alloc_vmap_area(unsigned long size,
    unsigned long align,
    unsigned long vstart, unsigned long vend,
    int node, gfp_t gfp_mask,
    - unsigned long va_flags)
    + unsigned long va_flags, struct vm_struct *vm)
    {
    struct vmap_area *va;
    unsigned long freed;
    @@ -1627,9 +1627,12 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,

    va->va_start = addr;
    va->va_end = addr + size;
    - va->vm = NULL;
    + va->vm = vm;
    va->flags = va_flags;

    + if (vm != NULL)
    + vm->addr = (void *)addr;
    +
    spin_lock(&vmap_area_lock);
    insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
    spin_unlock(&vmap_area_lock);
    @@ -2039,7 +2042,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
    va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
    VMALLOC_START, VMALLOC_END,
    node, gfp_mask,
    - VMAP_RAM|VMAP_BLOCK);
    + VMAP_RAM|VMAP_BLOCK,
    + NULL);
    if (IS_ERR(va)) {
    kfree(vb);
    return ERR_CAST(va);
    @@ -2394,7 +2398,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
    struct vmap_area *va;
    va = alloc_vmap_area(size, PAGE_SIZE,
    VMALLOC_START, VMALLOC_END,
    - node, GFP_KERNEL, VMAP_RAM);
    + node, GFP_KERNEL, VMAP_RAM,
    + NULL);
    if (IS_ERR(va))
    return NULL;

    @@ -2548,14 +2553,6 @@ static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
    va->vm = vm;
    }

    -static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
    - unsigned long flags, const void *caller)
    -{
    - spin_lock(&vmap_area_lock);
    - setup_vmalloc_vm_locked(vm, va, flags, caller);
    - spin_unlock(&vmap_area_lock);
    -}
    -
    static void clear_vm_uninitialized_flag(struct vm_struct *vm)
    {
    /*
    @@ -2592,14 +2589,16 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
    if (!(flags & VM_NO_GUARD))
    size += PAGE_SIZE;

    - va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0);
    + area->flags = flags;
    + area->caller = caller;
    + area->size = size;
    +
    + va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0, area);
    if (IS_ERR(va)) {
    kfree(area);
    return NULL;
    }

    - setup_vmalloc_vm(area, va, flags, caller);
    -
    /*
    * Mark pages for non-VM_ALLOC mappings as accessible. Do it now as a
    * best-effort approach, as they can be mapped outside of vmalloc code.
    base-commit: de927f6c0b07d9e698416c5b287c521b07694cac
    --
    2.43.0


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