linux-kernel - Re: [PATCH v3 11/12] mm/debug_vm

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Message-ID: <54bd0724-90c3-564b-fa3a-2e6c86ec609b@redhat.com>
Date:   Thu, 22 Jul 2021 16:53:10 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org, chuhu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v3 11/12] mm/debug_vm_pgtable: Remove unused code

Hi Anshuman,

On 7/22/21 2:51 PM, Anshuman Khandual wrote:
> Small nit for the subject line.
> 
> s/Remove unused code/Remove unused page table debug elements/
> 

Ok. Will apply the replacement in v4, thanks!

> On 7/19/21 6:36 PM, Gavin Shan wrote:
>> The variables used by old implementation isn't needed as we switched
>> to "struct pgtable_debug_args". Lets remove them and related code in
>> debug_vm_pgtable().
>>
>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>> ---
>>   mm/debug_vm_pgtable.c | 54 -------------------------------------------
>>   1 file changed, 54 deletions(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 5ebacc940b68..4f7bf1c9724a 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -1124,14 +1124,6 @@ static int __init init_args(struct pgtable_debug_args *args)
>>   static int __init debug_vm_pgtable(void)
>>   {
>>   	struct pgtable_debug_args args;
>> -	struct vm_area_struct *vma;
>> -	struct mm_struct *mm;
>> -	pgd_t *pgdp;
>> -	p4d_t *p4dp;
>> -	pud_t *pudp;
>> -	pmd_t *pmdp, *saved_pmdp, pmd;
>> -	pgtable_t saved_ptep;
>> -	unsigned long vaddr;
>>   	spinlock_t *ptl = NULL;
>>   	int idx, ret;
>>   
>> @@ -1140,41 +1132,6 @@ static int __init debug_vm_pgtable(void)
>>   	if (ret)
>>   		return ret;
>>   
>> -	vaddr = get_random_vaddr();
>> -	mm = mm_alloc();
>> -	if (!mm) {
>> -		pr_err("mm_struct allocation failed\n");
>> -		return 1;
>> -	}
>> -
>> -	vma = vm_area_alloc(mm);
>> -	if (!vma) {
>> -		pr_err("vma allocation failed\n");
>> -		return 1;
>> -	}
>> -
>> -	pgdp = pgd_offset(mm, vaddr);
>> -	p4dp = p4d_alloc(mm, pgdp, vaddr);
>> -	pudp = pud_alloc(mm, p4dp, vaddr);
>> -	pmdp = pmd_alloc(mm, pudp, vaddr);
>> -	/*
>> -	 * Allocate pgtable_t
>> -	 */
>> -	if (pte_alloc(mm, pmdp)) {
>> -		pr_err("pgtable allocation failed\n");
>> -		return 1;
>> -	}
>> -
>> -	/*
>> -	 * Save all the page table page addresses as the page table
>> -	 * entries will be used for testing with random or garbage
>> -	 * values. These saved addresses will be used for freeing
>> -	 * page table pages.
>> -	 */
> 
> Please move this comment as is to the right place inside init_args()
> in the first patch itself. If possible all comments should be moved
> during the first patch and just the code gets dropped here.
> 

In PATCH[v3 01/12], We already had the comments in init_args() as below:

        /*
         * The above page table entries will be modified. Lets save the
         * page table entries so that they can be released when the tests
         * are completed.
         */


>> -	pmd = READ_ONCE(*pmdp);
>> -	saved_pmdp = pmd_offset(pudp, 0UL);
>> -	saved_ptep = pmd_pgtable(pmd);
>> -
>>   	/*
>>   	 * Iterate over the protection_map[] to make sure that all
>>   	 * the basic page table transformation validations just hold
>> @@ -1256,17 +1213,6 @@ static int __init debug_vm_pgtable(void)
>>   	pgd_populate_tests(&args);
>>   	spin_unlock(&(args.mm->page_table_lock));
>>   
>> -	p4d_free(mm, p4d_offset(pgdp, 0UL));
>> -	pud_free(mm, pud_offset(p4dp, 0UL));
>> -	pmd_free(mm, saved_pmdp);
>> -	pte_free(mm, saved_ptep);
>> -
>> -	vm_area_free(vma);
>> -	mm_dec_nr_puds(mm);
>> -	mm_dec_nr_pmds(mm);
>> -	mm_dec_nr_ptes(mm);
>> -	mmdrop(mm);
>> -
>>   	destroy_args(&args);
>>   	return 0;
>>   }
>>

Thanks,
Gavin