[v10,12/25] mm: Move end_index check out of readahead loop
diff mbox series

Message ID 20200323202259.13363-13-willy@infradead.org
State Superseded
Headers show
Series
  • Change readahead API
Related show

Commit Message

Matthew Wilcox March 23, 2020, 8:22 p.m. UTC
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

By reducing nr_to_read, we can eliminate this check from inside the loop.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
---
 mm/readahead.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Comments

Eric Biggers March 23, 2020, 8:49 p.m. UTC | #1
On Mon, Mar 23, 2020 at 01:22:46PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> By reducing nr_to_read, we can eliminate this check from inside the loop.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>
> ---
>  mm/readahead.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/readahead.c b/mm/readahead.c
> index d01531ef9f3c..998fdd23c0b1 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -167,8 +167,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
>  		unsigned long lookahead_size)
>  {
>  	struct inode *inode = mapping->host;
> -	struct page *page;
> -	unsigned long end_index;	/* The last page we want to read */
>  	LIST_HEAD(page_pool);
>  	loff_t isize = i_size_read(inode);
>  	gfp_t gfp_mask = readahead_gfp_mask(mapping);
> @@ -178,22 +176,26 @@ void __do_page_cache_readahead(struct address_space *mapping,
>  		._index = index,
>  	};
>  	unsigned long i;
> +	pgoff_t end_index;	/* The last page we want to read */
>  
>  	if (isize == 0)
>  		return;
>  
> -	end_index = ((isize - 1) >> PAGE_SHIFT);
> +	end_index = (isize - 1) >> PAGE_SHIFT;
> +	if (index > end_index)
> +		return;
> +	/* Don't read past the page containing the last byte of the file */
> +	if (nr_to_read > end_index - index)
> +		nr_to_read = end_index - index + 1;
>  
>  	/*
>  	 * Preallocate as many pages as we will need.
>  	 */
>  	for (i = 0; i < nr_to_read; i++) {
> -		if (index + i > end_index)
> -			break;
> +		struct page *page = xa_load(&mapping->i_pages, index + i);
>  
>  		BUG_ON(index + i != rac._index + rac._nr_pages);
>  
> -		page = xa_load(&mapping->i_pages, index + i);
>  		if (page && !xa_is_value(page)) {
>  			/*
>  			 * Page already present?  Kick off the current batch of
> -- 

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric
Christoph Hellwig March 24, 2020, 8:40 a.m. UTC | #2
On Mon, Mar 23, 2020 at 01:22:46PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> By reducing nr_to_read, we can eliminate this check from inside the loop.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Patch
diff mbox series

diff --git a/mm/readahead.c b/mm/readahead.c
index d01531ef9f3c..998fdd23c0b1 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -167,8 +167,6 @@  void __do_page_cache_readahead(struct address_space *mapping,
 		unsigned long lookahead_size)
 {
 	struct inode *inode = mapping->host;
-	struct page *page;
-	unsigned long end_index;	/* The last page we want to read */
 	LIST_HEAD(page_pool);
 	loff_t isize = i_size_read(inode);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
@@ -178,22 +176,26 @@  void __do_page_cache_readahead(struct address_space *mapping,
 		._index = index,
 	};
 	unsigned long i;
+	pgoff_t end_index;	/* The last page we want to read */
 
 	if (isize == 0)
 		return;
 
-	end_index = ((isize - 1) >> PAGE_SHIFT);
+	end_index = (isize - 1) >> PAGE_SHIFT;
+	if (index > end_index)
+		return;
+	/* Don't read past the page containing the last byte of the file */
+	if (nr_to_read > end_index - index)
+		nr_to_read = end_index - index + 1;
 
 	/*
 	 * Preallocate as many pages as we will need.
 	 */
 	for (i = 0; i < nr_to_read; i++) {
-		if (index + i > end_index)
-			break;
+		struct page *page = xa_load(&mapping->i_pages, index + i);
 
 		BUG_ON(index + i != rac._index + rac._nr_pages);
 
-		page = xa_load(&mapping->i_pages, index + i);
 		if (page && !xa_is_value(page)) {
 			/*
 			 * Page already present?  Kick off the current batch of