Re: [PATCH v7 2/2] mm/vmalloc: Eliminated the lock contention from twice to once

[Baoquan He]

On 03/01/24 at 10:54am, rulinhuang wrote:
> When allocating a new memory area where the mapping address range is
> known, it is observed that the vmap_node->busy.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_node->busy.lock is contended.
> By doing so, the need to acquire the lock twice can also be eliminated
> to once.
> 
> With the above change, tested on intel sapphire rapids
> platform(224 vcpu), a 4% performance improvement is
> gained on stress-ng/pthread(https://github.com/ColinIanKing/stress-ng),
> which is the stress test of thread creations.
> 
> Co-developed-by: "Chen, Tim C" <tim.c.chen@xxxxxxxxx>
> Signed-off-by: "Chen, Tim C" <tim.c.chen@xxxxxxxxx>
> Co-developed-by: "King, Colin" <colin.king@xxxxxxxxx>
> Signed-off-by: "King, Colin" <colin.king@xxxxxxxxx>
> Signed-off-by: rulinhuang <rulin.huang@xxxxxxxxx>
> ---
> V1 -> V2: Avoided the partial initialization issue of vm and
> separated insert_vmap_area() from alloc_vmap_area()
> V2 -> V3: Rebased on 6.8-rc5
> V3 -> V4: Rebased on mm-unstable branch
> V4 -> V5: Canceled the split of alloc_vmap_area()
> and keep insert_vmap_area()
> V5 -> V6: Added bug_on
> V6 -> V7: Adjusted the macros
> ---
>  mm/vmalloc.c | 52 ++++++++++++++++++++++++----------------------------
>  1 file changed, 24 insertions(+), 28 deletions(-)

LGTM,

Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>

> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index fc027a61c12e..5b7c9156d8da 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1972,15 +1972,26 @@ node_alloc(unsigned long size, unsigned long align,
>  	return va;
>  }
>  
> +static inline void setup_vmalloc_vm(struct vm_struct *vm,
> +	struct vmap_area *va, unsigned long flags, const void *caller)
> +{
> +	vm->flags = flags;
> +	vm->addr = (void *)va->va_start;
> +	vm->size = va->va_end - va->va_start;
> +	vm->caller = caller;
> +	va->vm = vm;
> +}
> +
>  /*
>   * 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,
> +				unsigned long flags, const void *caller)
>  {
>  	struct vmap_node *vn;
>  	struct vmap_area *va;
> @@ -2043,6 +2054,11 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	va->vm = NULL;
>  	va->flags = (va_flags | vn_id);
>  
> +	if (vm) {
> +		BUG_ON(va_flags & VMAP_RAM);
> +		setup_vmalloc_vm(vm, va, flags, caller);
> +	}
> +
>  	vn = addr_to_node(va->va_start);
>  
>  	spin_lock(&vn->busy.lock);
> @@ -2486,7 +2502,8 @@ 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,
> +					0, NULL);
>  	if (IS_ERR(va)) {
>  		kfree(vb);
>  		return ERR_CAST(va);
> @@ -2843,7 +2860,8 @@ 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, 0, NULL);
>  		if (IS_ERR(va))
>  			return NULL;
>  
> @@ -2946,26 +2964,6 @@ void __init vm_area_register_early(struct vm_struct *vm, size_t align)
>  	kasan_populate_early_vm_area_shadow(vm->addr, vm->size);
>  }
>  
> -static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
> -	struct vmap_area *va, unsigned long flags, const void *caller)
> -{
> -	vm->flags = flags;
> -	vm->addr = (void *)va->va_start;
> -	vm->size = va->va_end - va->va_start;
> -	vm->caller = caller;
> -	va->vm = vm;
> -}
> -
> -static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
> -			      unsigned long flags, const void *caller)
> -{
> -	struct vmap_node *vn = addr_to_node(va->va_start);
> -
> -	spin_lock(&vn->busy.lock);
> -	setup_vmalloc_vm_locked(vm, va, flags, caller);
> -	spin_unlock(&vn->busy.lock);
> -}
> -
>  static void clear_vm_uninitialized_flag(struct vm_struct *vm)
>  {
>  	/*
> @@ -3002,14 +3000,12 @@ 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);
> +	va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0, area, flags, caller);
>  	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.
> @@ -4584,7 +4580,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  
>  		spin_lock(&vn->busy.lock);
>  		insert_vmap_area(vas[area], &vn->busy.root, &vn->busy.head);
> -		setup_vmalloc_vm_locked(vms[area], vas[area], VM_ALLOC,
> +		setup_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
>  				 pcpu_get_vm_areas);
>  		spin_unlock(&vn->busy.lock);
>  	}
> -- 
> 2.43.0
>