linux-kernel - Re: [PATCH 2/2] mm/khugepaged: Convert release_pte

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Message-ID: <707cd2b6-4350-4171-1e0c-f63ea5db7ece@ghiti.fr>
Date:   Mon, 13 Feb 2023 16:55:06 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 2/2] mm/khugepaged: Convert release_pte_pages() to use
 folios

Hi Matthew,

On 2/13/23 16:50, Matthew Wilcox wrote:
> On Mon, Feb 13, 2023 at 04:28:05PM +0100, Alexandre Ghiti wrote:
>> The issue lies here: before using pteval in pfn_folio(), we should test it.
>> The following patch fixes the issue for me:
> Thanks for debugging it.  I'd rather see this written as ...
>
> 		pte_t pteval = *_pte;
> +		unsigned long pfn;
>
> +		if (pte_none(pteval))
> +			continue;
> +		pfn = pte_pfn(pteval);
> +		if (is_zero_pfn(pfn))
> +			continue;
> +		folio = pfn_folio(pfn);
> +		if (folio_test_large(folio))
> +			continue;
> 		release_pte_folio(folio);
>
> makes sense?


Sure, that's fine by me, I can send that or I'll add my tested-by on 
what you send, whatever suits you.

Alex


>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index eb38bd1b1b2f..fef3414b481b 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -514,10 +514,12 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
>>          while (--_pte >= pte) {
>>                  pte_t pteval = *_pte;
>>
>> -               folio = pfn_folio(pte_pfn(pteval));
>> -               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
>> -                               !folio_test_large(folio))
>> -                       release_pte_folio(folio);
>> +               if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) {
>> +                       folio = pfn_folio(pte_pfn(pteval));
>> +
>> +                       if (!folio_test_large(folio))
>> +                               release_pte_folio(folio);
>> +               }
>>          }
>>
>>          list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
>>
>>
>> @Marek: could you give it a try?
>>
>> I can send a separate patch if needed, let me know.
>>
>> Thanks,
>>
>> Alex
>>
>>
>>>>     		if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
>>>> -				!PageCompound(page))
>>>> -			release_pte_page(page);
>>>> +				!folio_test_large(folio))
>>>> +			release_pte_folio(folio);
>>>>     	}
>>>> -	list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
>>>> -		list_del(&page->lru);
>>>> -		release_pte_page(page);
>>>> +	list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
>>>> +		list_del(&folio->lru);
>>>> +		release_pte_folio(folio);
>>>>     	}
>>>>     }
>>> Best regards