linux-kernel - Re: [PATCH RFC 2/2] mm: Rework swap handling of zap_pte

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Date:   Mon, 15 Nov 2021 22:21:18 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Peter Xu <peterx@...hat.com>
CC:     <peterx@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
        Yang Shi <shy828301@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH RFC 2/2] mm: Rework swap handling of zap_pte_range

Hi Peter,

I was having trouble applying this cleanly to any of my local trees so was
wondering which sha1 should I be applying this on top of? Thanks.

 - Alistair

On Wednesday, 10 November 2021 7:29:52 PM AEDT 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.
> 
> 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 | 25 ++++++++-----------------
>  1 file changed, 8 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e454f3c6aeb9..e5d59a6b6479 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1326,6 +1326,8 @@ 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;
>  
> @@ -1333,8 +1335,6 @@ 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(zap_skip_check_mapping(details, page)))
>  				continue;
> @@ -1368,32 +1368,23 @@ 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(zap_skip_check_mapping(details, page)))
>  				continue;
> -			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
>  			rss[mm_counter(page)]--;
> -
>  			if (is_device_private_entry(entry))
>  				page_remove_rmap(page, false);
> -
>  			put_page(page);
> -			continue;
> -		}
> -
> -		if (!non_swap_entry(entry))
> -			rss[MM_SWAPENTS]--;
> -		else if (is_migration_entry(entry)) {
> -			struct page *page;
> -
> +		} else if (is_migration_entry(entry)) {
>  			page = pfn_swap_entry_to_page(entry);
>  			if (unlikely(zap_skip_check_mapping(details, page)))
>  				continue;
>  			rss[mm_counter(page)]--;
> +		} else if (!non_swap_entry(entry)) {
> +			rss[MM_SWAPENTS]--;
> +			if (unlikely(!free_swap_and_cache(entry)))
> +				print_bad_pte(vma, addr, ptent, NULL);
>  		}
> -		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);
>  
>