linux-kernel - Re: [PATCH v4 6/6] mm: swap: entirely map large folios found in swapcache

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Date: Thu, 09 May 2024 15:44:25 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org,  linux-mm@...ck.org,
  baolin.wang@...ux.alibaba.com,  chrisl@...nel.org,  david@...hat.com,
  hanchuanhua@...o.com,  hannes@...xchg.org,  hughd@...gle.com,
  kasong@...cent.com,  linux-kernel@...r.kernel.org,  ryan.roberts@....com,
  surenb@...gle.com,  v-songbaohua@...o.com,  willy@...radead.org,
  xiang@...nel.org,  yosryahmed@...gle.com,  yuzhao@...gle.com,
  ziy@...dia.com
Subject: Re: [PATCH v4 6/6] mm: swap: entirely map large folios found in
 swapcache

Barry Song <21cnbao@...il.com> writes:

> From: Chuanhua Han <hanchuanhua@...o.com>
>
> When a large folio is found in the swapcache, the current implementation
> requires calling do_swap_page() nr_pages times, resulting in nr_pages
> page faults. This patch opts to map the entire large folio at once to
> minimize page faults. Additionally, redundant checks and early exits
> for ARM64 MTE restoring are removed.
>
> Signed-off-by: Chuanhua Han <hanchuanhua@...o.com>
> Co-developed-by: Barry Song <v-songbaohua@...o.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> Reviewed-by: Ryan Roberts <ryan.roberts@....com>

LGTM, Thanks!  Feel free to add

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

in the future version.

> ---
>  mm/memory.c | 59 +++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 48 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index d9434df24d62..8b9e4cab93ed 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3968,6 +3968,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  	pte_t pte;
>  	vm_fault_t ret = 0;
>  	void *shadow = NULL;
> +	int nr_pages;
> +	unsigned long page_idx;
> +	unsigned long address;
> +	pte_t *ptep;
>  
>  	if (!pte_unmap_same(vmf))
>  		goto out;
> @@ -4166,6 +4170,38 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  		goto out_nomap;
>  	}
>  
> +	nr_pages = 1;
> +	page_idx = 0;
> +	address = vmf->address;
> +	ptep = vmf->pte;
> +	if (folio_test_large(folio) && folio_test_swapcache(folio)) {
> +		int nr = folio_nr_pages(folio);
> +		unsigned long idx = folio_page_idx(folio, page);
> +		unsigned long folio_start = address - idx * PAGE_SIZE;
> +		unsigned long folio_end = folio_start + nr * PAGE_SIZE;
> +		pte_t *folio_ptep;
> +		pte_t folio_pte;
> +
> +		if (unlikely(folio_start < max(address & PMD_MASK, vma->vm_start)))
> +			goto check_folio;
> +		if (unlikely(folio_end > pmd_addr_end(address, vma->vm_end)))
> +			goto check_folio;
> +
> +		folio_ptep = vmf->pte - idx;
> +		folio_pte = ptep_get(folio_ptep);
> +		if (!pte_same(folio_pte, pte_move_swp_offset(vmf->orig_pte, -idx)) ||
> +		    swap_pte_batch(folio_ptep, nr, folio_pte) != nr)
> +			goto check_folio;
> +
> +		page_idx = idx;
> +		address = folio_start;
> +		ptep = folio_ptep;
> +		nr_pages = nr;
> +		entry = folio->swap;
> +		page = &folio->page;
> +	}
> +
> +check_folio:
>  	/*
>  	 * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte
>  	 * must never point at an anonymous page in the swapcache that is
> @@ -4225,12 +4261,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  	 * We're already holding a reference on the page but haven't mapped it
>  	 * yet.
>  	 */
> -	swap_free(entry);
> +	swap_free_nr(entry, nr_pages);
>  	if (should_try_to_free_swap(folio, vma, vmf->flags))
>  		folio_free_swap(folio);
>  
> -	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
> -	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
> +	add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
> +	add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
>  	pte = mk_pte(page, vma->vm_page_prot);
>  
>  	/*
> @@ -4247,27 +4283,28 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  		}
>  		rmap_flags |= RMAP_EXCLUSIVE;
>  	}
> -	flush_icache_page(vma, page);
> +	folio_ref_add(folio, nr_pages - 1);
> +	flush_icache_pages(vma, page, nr_pages);
>  	if (pte_swp_soft_dirty(vmf->orig_pte))
>  		pte = pte_mksoft_dirty(pte);
>  	if (pte_swp_uffd_wp(vmf->orig_pte))
>  		pte = pte_mkuffd_wp(pte);
> -	vmf->orig_pte = pte;
> +	vmf->orig_pte = pte_advance_pfn(pte, page_idx);
>  
>  	/* ksm created a completely new copy */
>  	if (unlikely(folio != swapcache && swapcache)) {
> -		folio_add_new_anon_rmap(folio, vma, vmf->address);
> +		folio_add_new_anon_rmap(folio, vma, address);
>  		folio_add_lru_vma(folio, vma);
>  	} else {
> -		folio_add_anon_rmap_pte(folio, page, vma, vmf->address,
> +		folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
>  					rmap_flags);
>  	}
>  
>  	VM_BUG_ON(!folio_test_anon(folio) ||
>  			(pte_write(pte) && !PageAnonExclusive(page)));
> -	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
> -	arch_do_swap_page_nr(vma->vm_mm, vma, vmf->address,
> -			pte, vmf->orig_pte, 1);
> +	set_ptes(vma->vm_mm, address, ptep, pte, nr_pages);
> +	arch_do_swap_page_nr(vma->vm_mm, vma, address,
> +			pte, pte, nr_pages);
>  
>  	folio_unlock(folio);
>  	if (folio != swapcache && swapcache) {
> @@ -4291,7 +4328,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  	}
>  
>  	/* No need to invalidate - it was non-present before */
> -	update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
> +	update_mmu_cache_range(vmf, vma, address, ptep, nr_pages);
>  unlock:
>  	if (vmf->pte)
>  		pte_unmap_unlock(vmf->pte, vmf->ptl);

--
Best Regards,
Huang, Ying