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

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Message-ID: <587a3a75-bbee-2ae4-8e69-563b9f277306@huawei.com>
Date:   Fri, 27 Aug 2021 16:36:28 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Catalin Marinas <catalin.marinas@....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 2021/8/26 1:59, Catalin Marinas wrote:
> 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.

Hi Catalin, thank for your review, I will update in the next version,

Could you take a look the following change, is it OK?

void __init vm_area_register_early(struct vm_struct *vm, size_t align)

{

          struct vm_struct *next, *cur, **p;
          unsigned long addr = ALIGN(VMALLOC_START, align);
BUG_ON(vmap_initialized);

          for (p = &vmlist; (cur = *p) != NULL, next = cur->next; p = 
&next) {
                  addr = ALIGN((unsigned long)cur->addr + cur->size, 
align);
                  if (next && (unsigned long)next->addr - addr >= 
vm->size) {
                          p = &next;
break;
}
}

          BUG_ON(addr > VMALLOC_END - vm->size);
          vm->addr = (void *)addr;
          vm->next = *p;
          *p = vm;
}


>