lkml.org 
[lkml]   [2022]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v2 1/3] mm: vmalloc: Avoid of calling __find_vmap_area() twise in __vunmap()
    Date
    Currently __vunmap() path calls __find_vmap_area() two times. One on
    entry to check that area exists, second time inside remove_vm_area()
    function that also performs a new search of VA.

    In order to improvie it from a performance point of view we split
    remove_vm_area() into two new parts:
    - find_unlink_vmap_area() that does a search and unlink from tree;
    - __remove_vm_area() that does a removing but without searching.

    In this case there is no any functional change for remove_vm_area()
    whereas vm_remove_mappings(), where a second search happens, switches
    to the __remove_vm_area() variant where already detached VA is passed
    as a parameter, so there is no need to find it again.

    Performance wise, i use test_vmalloc.sh with 32 threads doing alloc
    free on a 64-CPUs-x86_64-box:

    perf without this patch:
    - 31.41% 0.50% vmalloc_test/10 [kernel.vmlinux] [k] __vunmap
    - 30.92% __vunmap
    - 17.67% _raw_spin_lock
    native_queued_spin_lock_slowpath
    - 12.33% remove_vm_area
    - 11.79% free_vmap_area_noflush
    - 11.18% _raw_spin_lock
    native_queued_spin_lock_slowpath
    0.76% free_unref_page

    perf with this patch:
    - 11.35% 0.13% vmalloc_test/14 [kernel.vmlinux] [k] __vunmap
    - 11.23% __vunmap
    - 8.28% find_unlink_vmap_area
    - 7.95% _raw_spin_lock
    7.44% native_queued_spin_lock_slowpath
    - 1.93% free_vmap_area_noflush
    - 0.56% _raw_spin_lock
    0.53% native_queued_spin_lock_slowpath
    0.60% __vunmap_range_noflush

    __vunmap() consumes around ~20% less CPU cycles on this test.

    Reported-by: Roman Gushchin <roman.gushchin@linux.dev>
    Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
    ---
    mm/vmalloc.c | 66 +++++++++++++++++++++++++++++++++-------------------
    1 file changed, 42 insertions(+), 24 deletions(-)

    diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    index 9e30f0b39203..28030d2441f1 100644
    --- a/mm/vmalloc.c
    +++ b/mm/vmalloc.c
    @@ -1825,9 +1825,11 @@ static void free_vmap_area_noflush(struct vmap_area *va)
    unsigned long va_start = va->va_start;
    unsigned long nr_lazy;

    - spin_lock(&vmap_area_lock);
    - unlink_va(va, &vmap_area_root);
    - spin_unlock(&vmap_area_lock);
    + if (!list_empty(&va->list)) {
    + spin_lock(&vmap_area_lock);
    + unlink_va(va, &vmap_area_root);
    + spin_unlock(&vmap_area_lock);
    + }

    nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
    PAGE_SHIFT, &vmap_lazy_nr);
    @@ -1871,6 +1873,19 @@ struct vmap_area *find_vmap_area(unsigned long addr)
    return va;
    }

    +static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
    +{
    + struct vmap_area *va;
    +
    + spin_lock(&vmap_area_lock);
    + va = __find_vmap_area(addr, &vmap_area_root);
    + if (va)
    + unlink_va(va, &vmap_area_root);
    + spin_unlock(&vmap_area_lock);
    +
    + return va;
    +}
    +
    /*** Per cpu kva allocator ***/

    /*
    @@ -2591,6 +2606,20 @@ struct vm_struct *find_vm_area(const void *addr)
    return va->vm;
    }

    +static struct vm_struct *__remove_vm_area(struct vmap_area *va)
    +{
    + struct vm_struct *vm;
    +
    + if (!va || !va->vm)
    + return NULL;
    +
    + vm = va->vm;
    + kasan_free_module_shadow(vm);
    + free_unmap_vmap_area(va);
    +
    + return vm;
    +}
    +
    /**
    * remove_vm_area - find and remove a continuous kernel virtual area
    * @addr: base address
    @@ -2607,22 +2636,8 @@ struct vm_struct *remove_vm_area(const void *addr)

    might_sleep();

    - spin_lock(&vmap_area_lock);
    - va = __find_vmap_area((unsigned long)addr, &vmap_area_root);
    - if (va && va->vm) {
    - struct vm_struct *vm = va->vm;
    -
    - va->vm = NULL;
    - spin_unlock(&vmap_area_lock);
    -
    - kasan_free_module_shadow(vm);
    - free_unmap_vmap_area(va);
    -
    - return vm;
    - }
    -
    - spin_unlock(&vmap_area_lock);
    - return NULL;
    + va = find_unlink_vmap_area((unsigned long) addr);
    + return __remove_vm_area(va);
    }

    static inline void set_area_direct_map(const struct vm_struct *area,
    @@ -2637,15 +2652,16 @@ static inline void set_area_direct_map(const struct vm_struct *area,
    }

    /* Handle removing and resetting vm mappings related to the vm_struct. */
    -static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
    +static void vm_remove_mappings(struct vmap_area *va, int deallocate_pages)
    {
    + struct vm_struct *area = va->vm;
    unsigned long start = ULONG_MAX, end = 0;
    unsigned int page_order = vm_area_page_order(area);
    int flush_reset = area->flags & VM_FLUSH_RESET_PERMS;
    int flush_dmap = 0;
    int i;

    - remove_vm_area(area->addr);
    + __remove_vm_area(va);

    /* If this is not VM_FLUSH_RESET_PERMS memory, no need for the below. */
    if (!flush_reset)
    @@ -2690,6 +2706,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
    static void __vunmap(const void *addr, int deallocate_pages)
    {
    struct vm_struct *area;
    + struct vmap_area *va;

    if (!addr)
    return;
    @@ -2698,19 +2715,20 @@ static void __vunmap(const void *addr, int deallocate_pages)
    addr))
    return;

    - area = find_vm_area(addr);
    - if (unlikely(!area)) {
    + va = find_unlink_vmap_area((unsigned long)addr);
    + if (unlikely(!va)) {
    WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
    addr);
    return;
    }

    + area = va->vm;
    debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
    debug_check_no_obj_freed(area->addr, get_vm_area_size(area));

    kasan_poison_vmalloc(area->addr, get_vm_area_size(area));

    - vm_remove_mappings(area, deallocate_pages);
    + vm_remove_mappings(va, deallocate_pages);

    if (deallocate_pages) {
    int i;
    --
    2.30.2
    \
     
     \ /
      Last update: 2023-03-26 23:17    [W:7.141 / U:0.032 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site