linux-kernel - Re: [PATCH v4 06/12] mm/debug_vm_pgtable: Use struct pgtable_debug

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Date:   Thu, 29 Jul 2021 09:54:06 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, gerald.schaefer@...ux.ibm.com,
        aneesh.kumar@...ux.ibm.com, christophe.leroy@...roup.eu,
        cai@....pw, catalin.marinas@....com, will@...nel.org,
        akpm@...ux-foundation.org, chuhu@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v4 06/12] mm/debug_vm_pgtable: Use struct
 pgtable_debug_args in migration and thp tests

Hi Anshuman,

On 7/28/21 9:08 PM, Anshuman Khandual wrote:
> On 7/27/21 11:43 AM, Gavin Shan wrote:
>> This uses struct pgtable_debug_args in the migration and thp test
>> functions. It's notable that the pre-allocated page is used in
>> swap_migration_tests() as set_pte_at() is used there.
>>
>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>> ---
>>   mm/debug_vm_pgtable.c | 28 ++++++++++++++--------------
>>   1 file changed, 14 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index bc153cad9045..9136195efde3 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -845,7 +845,7 @@ static void __init pmd_swap_tests(struct pgtable_debug_args *args)
>>   static void __init pmd_swap_tests(struct pgtable_debug_args *args) { }
>>   #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */
>>   
>> -static void __init swap_migration_tests(void)
>> +static void __init swap_migration_tests(struct pgtable_debug_args *args)
>>   {
>>   	struct page *page;
>>   	swp_entry_t swp;
>> @@ -861,9 +861,10 @@ static void __init swap_migration_tests(void)
>>   	 * problematic. Lets allocate a dedicated page explicitly for this
>>   	 * purpose that will be freed subsequently.
>>   	 */
>> -	page = alloc_page(GFP_KERNEL);
>> +	page = (args->pte_pfn != ULONG_MAX) ?
>> +	       pfn_to_page(args->pte_pfn) : NULL;
>>   	if (!page) {
>> -		pr_err("page allocation failed\n");
>> +		pr_err("no page available\n");
>>   		return;
>>   	}
> 
> Please check for a valid page earlier in the function and return. Otherwise
> this calls out the page unavailability (after starting the test), which is
> inconsistent with all other functions like pxx_advanced_tests().
> 
> [    1.051633] debug_vm_pgtable: [pte_swap_tests           ]: Validating PTE swap
> [    1.052697] debug_vm_pgtable: [pmd_swap_tests           ]: Validating PMD swap
> [    1.053765] debug_vm_pgtable: [swap_migration_tests     ]: Validating swap migration <=====
> [    1.054900] debug_vm_pgtable: [swap_migration_tests     ]: no page available         <=====
> 
> Should do this just before pr_info("Validating swap migration\n").
> 
> ......
> page = (args->pte_pfn != ULONG_MAX) ? pfn_to_page(args->pte_pfn) : NULL;
> if (!page)
> 	return;
> .....
> 

Yes. The order of error messages are sticky to original implementation, but
it'd better to be consistent with the new order we have in this series. I
will adjust in v5.

Thanks,
Gavin