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From: Alistair Popple <apopple@nvidia.com>
To: Hugh Dickins <hughd@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
	Peter Xu <peterx@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>,
	Jerome Glisse <jglisse@redhat.com>, <peterx@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Miaohe Lin <linmiaohe@huawei.com>, Yang Shi <shy828301@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v2 4/5] mm: Add zap_skip_check_mapping() helper
Date: Fri, 3 Sep 2021 10:58:53 +1000	[thread overview]
Message-ID: <1771631.QAr93JHi05@nvdebian> (raw)
In-Reply-To: <20210902201819.53343-1-peterx@redhat.com>

On Friday, 3 September 2021 6:18:19 AM AEST Peter Xu wrote:
> Use the helper for the checks.  Rename "check_mapping" into "zap_mapping"
> because "check_mapping" looks like a bool but in fact it stores the mapping
> itself.  When it's set, we check the mapping (it must be non-NULL).  When it's
> cleared we skip the check, which works like the old way.
>
> Move the duplicated comments to the helper too.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  include/linux/mm.h | 15 ++++++++++++++-
>  mm/memory.c        | 29 ++++++-----------------------
>  2 files changed, 20 insertions(+), 24 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 69259229f090..81e402a5fbc9 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1720,10 +1720,23 @@ extern void user_shm_unlock(size_t, struct ucounts *);
>   * Parameter block passed down to zap_pte_range in exceptional cases.
>   */
>  struct zap_details {
> -	struct address_space *check_mapping;	/* Check page->mapping if set */
> +	struct address_space *zap_mapping;	/* Check page->mapping if set */
>  	struct page *single_page;		/* Locked page to be unmapped */
>  };
>  
> +/*
> + * We set details->zap_mappings when we want to unmap shared but keep private
> + * pages. Return true if skip zapping this page, false otherwise.
> + */
> +static inline bool
> +zap_skip_check_mapping(struct zap_details *details, struct page *page)
> +{
> +	if (!details || !page)
> +		return false;
> +
> +	return details->zap_mapping != page_rmapping(page);

Shouldn't this check still be
details->zap_mapping && details->zap_mapping != page_rmapping(page)?

Previously we wouldn't skip zapping pages if even_cows == true (ie.
details->check_mapping == NULL). With this change the check when
even_cows == true becomes NULL != page_rmapping(page). Doesn't this mean we
will now skip zapping any pages with a mapping when even_cows == true?

> +}
> +
>  struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>  			     pte_t pte);
>  struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
> diff --git a/mm/memory.c b/mm/memory.c
> index 6bba3b9fef7c..e5ee8399d270 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1333,16 +1333,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  			struct page *page;
>  
>  			page = vm_normal_page(vma, addr, ptent);
> -			if (unlikely(details) && page) {
> -				/*
> -				 * unmap_shared_mapping_pages() wants to
> -				 * invalidate cache without truncating:
> -				 * unmap shared but keep private pages.
> -				 */
> -				if (details->check_mapping &&
> -				    details->check_mapping != page_rmapping(page))
> -					continue;
> -			}
> +			if (unlikely(zap_skip_check_mapping(details, page)))
> +				continue;
>
>  			ptent = ptep_get_and_clear_full(mm, addr, pte,
>  							tlb->fullmm);
>  			tlb_remove_tlb_entry(tlb, pte, addr);
> @@ -1375,17 +1367,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  		    is_device_exclusive_entry(entry)) {
>  			struct page *page = pfn_swap_entry_to_page(entry);
>  
> -			if (unlikely(details && details->check_mapping)) {
> -				/*
> -				 * unmap_shared_mapping_pages() wants to
> -				 * invalidate cache without truncating:
> -				 * unmap shared but keep private pages.
> -				 */
> -				if (details->check_mapping !=
> -				    page_rmapping(page))
> -					continue;
> -			}
> -
> +			if (unlikely(zap_skip_check_mapping(details, page)))
> +				continue;
>  			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
>  			rss[mm_counter(page)]--;
>  
> @@ -3368,7 +3351,7 @@ void unmap_mapping_page(struct page *page)
>  	first_index = page->index;
>  	last_index = page->index + thp_nr_pages(page) - 1;
>  
> -	details.check_mapping = mapping;
> +	details.zap_mapping = mapping;
>  	details.single_page = page;
>  
>  	i_mmap_lock_write(mapping);
> @@ -3396,7 +3379,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
>  	pgoff_t	first_index = start, last_index = start + nr - 1;
>  	struct zap_details details = { };
>  
> -	details.check_mapping = even_cows ? NULL : mapping;
> +	details.zap_mapping = even_cows ? NULL : mapping;
>  	if (last_index < first_index)
>  		last_index = ULONG_MAX;
>  
> 





  reply	other threads:[~2021-09-03  0:59 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 20:17 [PATCH v2 0/5] mm: A few cleanup patches around zap, shmem and uffd Peter Xu
2021-09-02 20:17 ` [PATCH v2 1/5] mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte Peter Xu
2021-09-03  7:42   ` David Hildenbrand
2021-09-03 20:00     ` Peter Xu
2021-09-03 20:02       ` David Hildenbrand
2021-09-02 20:17 ` [PATCH v2 2/5] mm: Clear vmf->pte after pte_unmap_same() returns Peter Xu
2021-09-08  1:12   ` Liam Howlett
2021-09-02 20:17 ` [PATCH v2 3/5] mm: Drop first_index/last_index in zap_details Peter Xu
2021-09-02 20:18 ` [PATCH v2 4/5] mm: Add zap_skip_check_mapping() helper Peter Xu
2021-09-03  0:58   ` Alistair Popple [this message]
2021-09-03  1:39     ` Peter Xu
2021-09-03  1:50       ` Alistair Popple
2021-09-03  7:07         ` David Hildenbrand
2021-09-02 20:18 ` [PATCH v2 5/5] mm: Add ZAP_FLAG_SKIP_SWAP and zap_flags Peter Xu
2021-09-03  7:25   ` David Hildenbrand
2021-09-03  7:31     ` David Hildenbrand
2021-09-08  0:43     ` Peter Xu
2021-09-08  0:35 ` [PATCH v2 0/5] mm: A few cleanup patches around zap, shmem and uffd Peter Xu

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