linux-kernel - Re: [PATCH 2/2] mm: vmalloc: Refactor vmalloc_dump

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Date: Tue, 30 Jan 2024 18:50:48 +0000
From: Lorenzo Stoakes <lstoakes@...il.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <willy@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 2/2] mm: vmalloc: Refactor vmalloc_dump_obj() function

On Wed, Jan 24, 2024 at 07:09:20PM +0100, Uladzislau Rezki (Sony) wrote:
> This patch tends to simplify the function in question,
> by removing an extra stack "objp" variable, returning
> back to an early exit approach if spin_trylock() fails
> or VA was not found.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index b8be601b056d..449f45b0e474 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4696,34 +4696,35 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  #ifdef CONFIG_PRINTK
>  bool vmalloc_dump_obj(void *object)
>  {
> -	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
>  	const void *caller;
> +	struct vm_struct *vm;
>  	struct vmap_area *va;
>  	struct vmap_node *vn;
>  	unsigned long addr;
>  	unsigned int nr_pages;
> -	bool success = false;
> -
> -	vn = addr_to_node((unsigned long)objp);
>
> -	if (spin_trylock(&vn->busy.lock)) {
> -		va = __find_vmap_area((unsigned long)objp, &vn->busy.root);
> +	addr = PAGE_ALIGN((unsigned long) object);
> +	vn = addr_to_node(addr);
>
> -		if (va && va->vm) {
> -			addr = (unsigned long)va->vm->addr;
> -			caller = va->vm->caller;
> -			nr_pages = va->vm->nr_pages;
> -			success = true;
> -		}
> +	if (!spin_trylock(&vn->busy.lock))
> +		return false;
>
> +	va = __find_vmap_area(addr, &vn->busy.root);
> +	if (!va || !va->vm) {
>  		spin_unlock(&vn->busy.lock);
> +		return false;
>  	}
>
> -	if (success)
> -		pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
> -			nr_pages, addr, caller);
> +	vm = va->vm;
> +	addr = (unsigned long) vm->addr;

Hmm not so nice to reuse addr here for something different, might be nice
to have separate obj_addr and vm_addr or something. But it's not critical!

> +	caller = vm->caller;
> +	nr_pages = vm->nr_pages;
> +	spin_unlock(&vn->busy.lock);
>
> -	return success;
> +	pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
> +		nr_pages, addr, caller);
> +
> +	return true;
>  }
>  #endif
>
> --
> 2.39.2
>

Other than the nit, which I don't insist on, this is a big improvement so,

Reviewed-by: Lorenzo Stoakes <lstoakes@...il.com>