Re: [PATCH v2 12/12] mm/filemap: Return only head pages from find_get_entries

[Jan Kara]

On Mon 14-09-20 14:00:42, Matthew Wilcox (Oracle) wrote:
> All callers now expect head (and base) pages, and can handle multiple
> head pages in a single batch, so make find_get_entries() behave that way.
> Also take the opportunity to make it use the pagevec infrastructure
> instead of open-coding how pvecs behave.  This has the side-effect of
> being able to append to a pagevec with existing contents, although we
> don't make use of that functionality anywhere yet.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

I'm just curious: What has happened to pagevec_lookup_entries() call in
invalidate_inode_pages2_range()? Your series appears to be based on a tree
where the call already does not exist...

								Honza

> ---
>  include/linux/pagemap.h |  2 --
>  mm/filemap.c            | 36 ++++++++----------------------------
>  mm/internal.h           |  2 ++
>  3 files changed, 10 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 788c280737e0..50d2c39b47ab 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -413,8 +413,6 @@ static inline struct page *find_subpage(struct page *head, pgoff_t index)
>  	return head + (index & (thp_nr_pages(head) - 1));
>  }
>  
> -unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
> -		pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
>  unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
>  			pgoff_t end, unsigned int nr_pages,
>  			struct page **pages);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a4ad294a34dc..dbe3f7050897 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1807,49 +1807,29 @@ static inline struct page *xas_find_get_entry(struct xa_state *xas,
>   * the mapping.  The entries are placed in @pvec.  find_get_entries()
>   * takes a reference on any actual pages it returns.
>   *
> - * The search returns a group of mapping-contiguous page cache entries
> - * with ascending indexes.  There may be holes in the indices due to
> - * not-present pages.
> + * The entries have ascending indexes.  The indices may not be consecutive
> + * due to not-present entries or THPs.
>   *
>   * Any shadow entries of evicted pages, or swap entries from
>   * shmem/tmpfs, are included in the returned array.
>   *
> - * If it finds a Transparent Huge Page, head or tail, find_get_entries()
> - * stops at that page: the caller is likely to have a better way to handle
> - * the compound page as a whole, and then skip its extent, than repeatedly
> - * calling find_get_entries() to return all its tails.
> - *
> - * Return: the number of pages and shadow entries which were found.
> + * Return: The number of entries which were found.
>   */
>  unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
>  		pgoff_t end, struct pagevec *pvec, pgoff_t *indices)
>  {
>  	XA_STATE(xas, &mapping->i_pages, start);
>  	struct page *page;
> -	unsigned int ret = 0;
> -	unsigned nr_entries = PAGEVEC_SIZE;
>  
>  	rcu_read_lock();
>  	while ((page = xas_find_get_entry(&xas, end, XA_PRESENT))) {
> -		/*
> -		 * Terminate early on finding a THP, to allow the caller to
> -		 * handle it all at once; but continue if this is hugetlbfs.
> -		 */
> -		if (!xa_is_value(page) && PageTransHuge(page) &&
> -				!PageHuge(page)) {
> -			page = find_subpage(page, xas.xa_index);
> -			nr_entries = ret + 1;
> -		}
> -
> -		indices[ret] = xas.xa_index;
> -		pvec->pages[ret] = page;
> -		if (++ret == nr_entries)
> +		indices[pvec->nr] = xas.xa_index;
> +		if (!pagevec_add(pvec, page))
>  			break;
>  	}
>  	rcu_read_unlock();
>  
> -	pvec->nr = ret;
> -	return ret;
> +	return pagevec_count(pvec);
>  }
>  
>  /**
> @@ -1868,8 +1848,8 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
>   * not returned.
>   *
>   * The entries have ascending indexes.  The indices may not be consecutive
> - * due to not-present entries, THP pages, pages which could not be locked
> - * or pages under writeback.
> + * due to not-present entries, THPs, pages which could not be locked or
> + * pages under writeback.
>   *
>   * Return: The number of entries which were found.
>   */
> diff --git a/mm/internal.h b/mm/internal.h
> index d17d9060902f..55da9860a54b 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -62,6 +62,8 @@ static inline void force_page_cache_readahead(struct address_space *mapping,
>  
>  struct page *find_get_entry(struct address_space *mapping, pgoff_t index);
>  struct page *find_lock_entry(struct address_space *mapping, pgoff_t index);
> +unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
> +		pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
>  unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
>  		pgoff_t end, struct pagevec *pvec, pgoff_t *indices);
>  
> -- 
> 2.28.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR