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Reply-To: Gavin Shan <gshan@redhat.com>
Subject: Re: [PATCH v3 10/12] mm/debug_vm_pgtable: Use struct
 pgtable_debug_args in PGD and P4D modifying tests
To:     Anshuman Khandual <anshuman.khandual@arm.com>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
        will@kernel.org, akpm@linux-foundation.org, chuhu@redhat.com,
        shan.gavin@gmail.com
References: <20210719130613.334901-1-gshan@redhat.com>
 <20210719130613.334901-11-gshan@redhat.com>
 <f636f6ae-ea37-aac6-47cd-ff97ceaa5268@arm.com>
From:   Gavin Shan <gshan@redhat.com>
Message-ID: <2992c680-abb9-9925-c009-3ae843dec903@redhat.com>
Date:   Thu, 22 Jul 2021 16:50:45 +1000
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Hi Anshuman,

On 7/22/21 3:09 PM, Anshuman Khandual wrote:
> On 7/19/21 6:36 PM, Gavin Shan wrote:
>> This uses struct pgtable_debug_args in PGD/P4D modifying tests. No
>> allocated huge page is used in these tests. Besides, the unused
>> variable @saved_p4dp and @saved_pudp are dropped.
> 
> Please dont drop  @saved_p4dp and @saved_pudp just yet.
> 

It seems you have concern why I drop unused variables in individual
patches. There is build warning 'unused variable', reported by 0-day.
So we need to drop these unused variables in individual patches, but
it make the review a bit harder :)

>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   mm/debug_vm_pgtable.c | 86 +++++++++++++++++++------------------------
>>   1 file changed, 38 insertions(+), 48 deletions(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 57b7ead0708b..5ebacc940b68 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -520,27 +520,26 @@ static void __init pud_populate_tests(struct pgtable_debug_args *args) { }
>>   #endif /* PAGETABLE_PUD_FOLDED */
>>   
>>   #ifndef __PAGETABLE_P4D_FOLDED
>> -static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp)
>> +static void __init p4d_clear_tests(struct pgtable_debug_args *args)
>>   {
>> -	p4d_t p4d = READ_ONCE(*p4dp);
>> +	p4d_t p4d = READ_ONCE(*(args->p4dp));
>>   
>> -	if (mm_pud_folded(mm))
>> +	if (mm_pud_folded(args->mm))
>>   		return;
>>   
>>   	pr_debug("Validating P4D clear\n");
>>   	p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE);
>> -	WRITE_ONCE(*p4dp, p4d);
>> -	p4d_clear(p4dp);
>> -	p4d = READ_ONCE(*p4dp);
>> +	WRITE_ONCE(*(args->p4dp), p4d);
>> +	p4d_clear(args->p4dp);
>> +	p4d = READ_ONCE(*(args->p4dp));
>>   	WARN_ON(!p4d_none(p4d));
>>   }
>>   
>> -static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
>> -				      pud_t *pudp)
>> +static void __init p4d_populate_tests(struct pgtable_debug_args *args)
>>   {
>>   	p4d_t p4d;
>>   
>> -	if (mm_pud_folded(mm))
>> +	if (mm_pud_folded(args->mm))
>>   		return;
>>   
>>   	pr_debug("Validating P4D populate\n");
>> @@ -548,34 +547,33 @@ static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
>>   	 * This entry points to next level page table page.
>>   	 * Hence this must not qualify as p4d_bad().
>>   	 */
>> -	pud_clear(pudp);
>> -	p4d_clear(p4dp);
>> -	p4d_populate(mm, p4dp, pudp);
>> -	p4d = READ_ONCE(*p4dp);
>> +	pud_clear(args->pudp);
>> +	p4d_clear(args->p4dp);
>> +	p4d_populate(args->mm, args->p4dp, args->start_pudp);
>> +	p4d = READ_ONCE(*(args->p4dp));
>>   	WARN_ON(p4d_bad(p4d));
>>   }
>>   
>> -static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp)
>> +static void __init pgd_clear_tests(struct pgtable_debug_args *args)
>>   {
>> -	pgd_t pgd = READ_ONCE(*pgdp);
>> +	pgd_t pgd = READ_ONCE(*(args->pgdp));
>>   
>> -	if (mm_p4d_folded(mm))
>> +	if (mm_p4d_folded(args->mm))
>>   		return;
>>   
>>   	pr_debug("Validating PGD clear\n");
>>   	pgd = __pgd(pgd_val(pgd) | RANDOM_ORVALUE);
>> -	WRITE_ONCE(*pgdp, pgd);
>> -	pgd_clear(pgdp);
>> -	pgd = READ_ONCE(*pgdp);
>> +	WRITE_ONCE(*(args->pgdp), pgd);
>> +	pgd_clear(args->pgdp);
>> +	pgd = READ_ONCE(*(args->pgdp));
>>   	WARN_ON(!pgd_none(pgd));
>>   }
>>   
>> -static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>> -				      p4d_t *p4dp)
>> +static void __init pgd_populate_tests(struct pgtable_debug_args *args)
>>   {
>>   	pgd_t pgd;
>>   
>> -	if (mm_p4d_folded(mm))
>> +	if (mm_p4d_folded(args->mm))
>>   		return;
>>   
>>   	pr_debug("Validating PGD populate\n");
>> @@ -583,23 +581,17 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>   	 * This entry points to next level page table page.
>>   	 * Hence this must not qualify as pgd_bad().
>>   	 */
>> -	p4d_clear(p4dp);
>> -	pgd_clear(pgdp);
>> -	pgd_populate(mm, pgdp, p4dp);
>> -	pgd = READ_ONCE(*pgdp);
>> +	p4d_clear(args->p4dp);
>> +	pgd_clear(args->pgdp);
>> +	pgd_populate(args->mm, args->pgdp, args->start_p4dp);
>> +	pgd = READ_ONCE(*(args->pgdp));
>>   	WARN_ON(pgd_bad(pgd));
>>   }
>>   #else  /* !__PAGETABLE_P4D_FOLDED */
>> -static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp) { }
>> -static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp) { }
>> -static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
>> -				      pud_t *pudp)
>> -{
>> -}
>> -static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>> -				      p4d_t *p4dp)
>> -{
>> -}
>> +static void __init p4d_clear_tests(struct pgtable_debug_args *args) { }
>> +static void __init pgd_clear_tests(struct pgtable_debug_args *args) { }
>> +static void __init p4d_populate_tests(struct pgtable_debug_args *args) { }
>> +static void __init pgd_populate_tests(struct pgtable_debug_args *args) { }
>>   #endif /* PAGETABLE_P4D_FOLDED */
>>   
>>   static void __init pte_clear_tests(struct pgtable_debug_args *args)
>> @@ -1135,8 +1127,8 @@ static int __init debug_vm_pgtable(void)
>>   	struct vm_area_struct *vma;
>>   	struct mm_struct *mm;
>>   	pgd_t *pgdp;
>> -	p4d_t *p4dp, *saved_p4dp;
>> -	pud_t *pudp, *saved_pudp;
>> +	p4d_t *p4dp;
>> +	pud_t *pudp;
>>   	pmd_t *pmdp, *saved_pmdp, pmd;
>>   	pgtable_t saved_ptep;
>>   	unsigned long vaddr;
>> @@ -1180,8 +1172,6 @@ static int __init debug_vm_pgtable(void)
>>   	 * page table pages.
>>   	 */
>>   	pmd = READ_ONCE(*pmdp);
>> -	saved_p4dp = p4d_offset(pgdp, 0UL);
>> -	saved_pudp = pud_offset(p4dp, 0UL);
>>   	saved_pmdp = pmd_offset(pudp, 0UL);
>>   	saved_ptep = pmd_pgtable(pmd);
>>   
>> @@ -1259,15 +1249,15 @@ static int __init debug_vm_pgtable(void)
>>   	pud_populate_tests(&args);
>>   	spin_unlock(ptl);
>>   
>> -	spin_lock(&mm->page_table_lock);
>> -	p4d_clear_tests(mm, p4dp);
>> -	pgd_clear_tests(mm, pgdp);
>> -	p4d_populate_tests(mm, p4dp, saved_pudp);
>> -	pgd_populate_tests(mm, pgdp, saved_p4dp);
>> -	spin_unlock(&mm->page_table_lock);
>> +	spin_lock(&(args.mm->page_table_lock));
>> +	p4d_clear_tests(&args);
>> +	pgd_clear_tests(&args);
>> +	p4d_populate_tests(&args);
>> +	pgd_populate_tests(&args);
>> +	spin_unlock(&(args.mm->page_table_lock));
>>   
>> -	p4d_free(mm, saved_p4dp);
>> -	pud_free(mm, saved_pudp);
>> +	p4d_free(mm, p4d_offset(pgdp, 0UL));
>> +	pud_free(mm, pud_offset(p4dp, 0UL));
> 
> Please keep @saved_pudp and @saved_p4dp declaration, assignment and
> usage unchanged for now. Drop them only during [PATCH 11/12]. So in
> each patch like these, drop the elements only if there is an unused
> warning during build.
> 
> There are two set of page table debug elements i.e old and new. The
> test is transitioning from old to new. Even after the transition is
> complete, the old elements are properly declared, initialized and
> freed up. Entire old set should be dropped only in [PATCH 11/12].
> 

As explained at the beginning and we need to drop the unused variable.

>>   	pmd_free(mm, saved_pmdp);
>>   	pte_free(mm, saved_ptep);
>>   
>>

Thanks,
Gavin