linux-kernel - Re: [PATCH v4 4/4] mm: Rework swap handling of zap_pte

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Message-ID: <b04fabea-6216-3808-44e8-0a2125bf0230@nvidia.com>
Date:   Wed, 16 Feb 2022 19:25:14 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alistair Popple <apopple@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v4 4/4] mm: Rework swap handling of zap_pte_range

On 2/16/22 1:48 AM, Peter Xu wrote:
> Clean the code up by merging the device private/exclusive swap entry handling
> with the rest, then we merge the pte clear operation too.

Maybe also mention that you reduced the code duplication in the 
is_device_private_entry() area, by letting it fall through to the common
pte_clear_not_present_full() at the end of the loop? Since you're listing
the other changes, that one seems worth mentioning.

> 
> struct* page is defined in multiple places in the function, move it upward.
> 
> free_swap_and_cache() is only useful for !non_swap_entry() case, put it into
> the condition.
> 
> No functional change intended.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/memory.c | 21 ++++++---------------
>  1 file changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index ffa8c7dfe9ad..cade96024349 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1361,6 +1361,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  	arch_enter_lazy_mmu_mode();
>  	do {
>  		pte_t ptent = *pte;
> +		struct page *page;
> +
>  		if (pte_none(ptent))
>  			continue;
>  
> @@ -1368,8 +1370,6 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  			break;
>  
>  		if (pte_present(ptent)) {
> -			struct page *page;
> -
>  			page = vm_normal_page(vma, addr, ptent);
>  			if (unlikely(!should_zap_page(details, page)))
>  				continue;
> @@ -1403,21 +1403,14 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  		entry = pte_to_swp_entry(ptent);
>  		if (is_device_private_entry(entry) ||
>  		    is_device_exclusive_entry(entry)) {
> -			struct page *page = pfn_swap_entry_to_page(entry);
> -
> +			page = pfn_swap_entry_to_page(entry);
>  			if (unlikely(!should_zap_page(details, page)))
>  				continue;
> -			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);

Yes! Good cleanup there.

>  			rss[mm_counter(page)]--;
> -
>  			if (is_device_private_entry(entry))
>  				page_remove_rmap(page, false);
> -
>  			put_page(page);
> -			continue;
> -		}
> -
> -		if (!non_swap_entry(entry)) {
> +		} else if (!non_swap_entry(entry)) {
>  			/*
>  			 * If this is a genuine swap entry, then it must be an
>  			 * private anon page.  If the caller wants to skip
> @@ -1426,9 +1419,9 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  			if (!should_zap_cows(details))
>  				continue;
>  			rss[MM_SWAPENTS]--;
> +			if (unlikely(!free_swap_and_cache(entry)))
> +				print_bad_pte(vma, addr, ptent, NULL);
>  		} else if (is_migration_entry(entry)) {
> -			struct page *page;
> -
>  			page = pfn_swap_entry_to_page(entry);
>  			if (!should_zap_page(details, page))
>  				continue;
> @@ -1441,8 +1434,6 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  			/* We should have covered all the swap entry types */
>  			WARN_ON_ONCE(1);
>  		}
> -		if (unlikely(!free_swap_and_cache(entry)))
> -			print_bad_pte(vma, addr, ptent, NULL);
>  		pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
>  	} while (pte++, addr += PAGE_SIZE, addr != end);
>  

Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA