linux-kernel - Re: [PATCH v3 1/3] vmalloc: Choose a better start address in vm_area_register

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Date:   Wed, 25 Aug 2021 18:59:53 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     will@...nel.org, ryabinin.a.a@...il.com, andreyknvl@...il.com,
        dvyukov@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, elver@...gle.com
Subject: Re: [PATCH v3 1/3] vmalloc: Choose a better start address in
 vm_area_register_early()

On Mon, Aug 09, 2021 at 05:37:48PM +0800, Kefeng Wang wrote:
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d5cd52805149..1e8fe08725b8 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2238,11 +2238,17 @@ void __init vm_area_add_early(struct vm_struct *vm)
>   */
>  void __init vm_area_register_early(struct vm_struct *vm, size_t align)
>  {
> -	static size_t vm_init_off __initdata;
> -	unsigned long addr;
> -
> -	addr = ALIGN(VMALLOC_START + vm_init_off, align);
> -	vm_init_off = PFN_ALIGN(addr + vm->size) - VMALLOC_START;
> +	struct vm_struct *head = vmlist, *curr, *next;
> +	unsigned long addr = ALIGN(VMALLOC_START, align);
> +
> +	while (head != NULL) {

Nitpick: I'd use the same pattern as in vm_area_add_early(), i.e. a
'for' loop. You might as well insert it directly than calling the add
function and going through the loop again. Not a strong preference
either way.

> +		next = head->next;
> +		curr = head;
> +		head = next;
> +		addr = ALIGN((unsigned long)curr->addr + curr->size, align);
> +		if (next && (unsigned long)next->addr - addr > vm->size)

Is greater or equal sufficient?

> +			break;
> +	}
>  
>  	vm->addr = (void *)addr;

Another nitpick: it's very unlikely on a 64-bit architecture but not
impossible on 32-bit to hit VMALLOC_END here. Maybe some BUG_ON.

-- 
Catalin