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Commit 0d3f9296 authored by Matthew Wilcox's avatar Matthew Wilcox
Browse files

page cache: Convert hole search to XArray 



The page cache offers the ability to search for a miss in the previous or
next N locations.  Rather than teach the XArray about the page cache's
definition of a miss, use xas_prev() and xas_next() to search the page
array.  This should be more efficient as it does not have to start the
lookup from the top for each index.

Signed-off-by: default avatarMatthew Wilcox <willy@infradead.org>
parent eb797a8e

fs/nfs/blocklayout/blocklayout.c

+1 −1
Original line number Diff line number Diff line
@@ -896,7 +896,7 @@ static u64 pnfs_num_cont_bytes(struct inode *inode, pgoff_t idx) 
	end = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);

	if (end != inode->i_mapping->nrpages) {

		rcu_read_lock();

		end = page_cache_next_hole(mapping, idx + 1, ULONG_MAX);

		end = page_cache_next_miss(mapping, idx + 1, ULONG_MAX);

		rcu_read_unlock();

	}

include/linux/pagemap.h

+2 −2
Original line number Diff line number Diff line
@@ -241,9 +241,9 @@ static inline gfp_t readahead_gfp_mask(struct address_space *x) 


typedef int filler_t(void *, struct page *);



pgoff_t page_cache_next_hole(struct address_space *mapping,

pgoff_t page_cache_next_miss(struct address_space *mapping,

			     pgoff_t index, unsigned long max_scan);

pgoff_t page_cache_prev_hole(struct address_space *mapping,

pgoff_t page_cache_prev_miss(struct address_space *mapping,

			     pgoff_t index, unsigned long max_scan);



#define FGP_ACCESSED		0x00000001

mm/filemap.c

+50 −60
Original line number Diff line number Diff line
@@ -1326,86 +1326,76 @@ int __lock_page_or_retry(struct page *page, struct mm_struct *mm, 
}



/**

 * page_cache_next_hole - find the next hole (not-present entry)

 * @mapping: mapping

 * @index: index

 * @max_scan: maximum range to search

 *

 * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the

 * lowest indexed hole.

 *

 * Returns: the index of the hole if found, otherwise returns an index

 * outside of the set specified (in which case 'return - index >=

 * max_scan' will be true). In rare cases of index wrap-around, 0 will

 * be returned.

 *

 * page_cache_next_hole may be called under rcu_read_lock. However,

 * like radix_tree_gang_lookup, this will not atomically search a

 * snapshot of the tree at a single point in time. For example, if a

 * hole is created at index 5, then subsequently a hole is created at

 * index 10, page_cache_next_hole covering both indexes may return 10

 * if called under rcu_read_lock.

 */

pgoff_t page_cache_next_hole(struct address_space *mapping,

 * page_cache_next_miss() - Find the next gap in the page cache.

 * @mapping: Mapping.

 * @index: Index.

 * @max_scan: Maximum range to search.

 *

 * Search the range [index, min(index + max_scan - 1, ULONG_MAX)] for the

 * gap with the lowest index.

 *

 * This function may be called under the rcu_read_lock.  However, this will

 * not atomically search a snapshot of the cache at a single point in time.

 * For example, if a gap is created at index 5, then subsequently a gap is

 * created at index 10, page_cache_next_miss covering both indices may

 * return 10 if called under the rcu_read_lock.

 *

 * Return: The index of the gap if found, otherwise an index outside the

 * range specified (in which case 'return - index >= max_scan' will be true).

 * In the rare case of index wrap-around, 0 will be returned.

 */

pgoff_t page_cache_next_miss(struct address_space *mapping,

			     pgoff_t index, unsigned long max_scan)

{

	unsigned long i;



	for (i = 0; i < max_scan; i++) {

		struct page *page;

	XA_STATE(xas, &mapping->i_pages, index);



		page = radix_tree_lookup(&mapping->i_pages, index);

		if (!page || xa_is_value(page))

	while (max_scan--) {

		void *entry = xas_next(&xas);

		if (!entry || xa_is_value(entry))

			break;

		index++;

		if (index == 0)

		if (xas.xa_index == 0)

			break;

	}



	return index;

	return xas.xa_index;

}

EXPORT_SYMBOL(page_cache_next_hole);

EXPORT_SYMBOL(page_cache_next_miss);



/**

 * page_cache_prev_hole - find the prev hole (not-present entry)

 * @mapping: mapping

 * @index: index

 * @max_scan: maximum range to search

 *

 * Search backwards in the range [max(index-max_scan+1, 0), index] for

 * the first hole.

 *

 * Returns: the index of the hole if found, otherwise returns an index

 * outside of the set specified (in which case 'index - return >=

 * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX

 * will be returned.

 *

 * page_cache_prev_hole may be called under rcu_read_lock. However,

 * like radix_tree_gang_lookup, this will not atomically search a

 * snapshot of the tree at a single point in time. For example, if a

 * hole is created at index 10, then subsequently a hole is created at

 * index 5, page_cache_prev_hole covering both indexes may return 5 if

 * called under rcu_read_lock.

 */

pgoff_t page_cache_prev_hole(struct address_space *mapping,

 * page_cache_prev_miss() - Find the next gap in the page cache.

 * @mapping: Mapping.

 * @index: Index.

 * @max_scan: Maximum range to search.

 *

 * Search the range [max(index - max_scan + 1, 0), index] for the

 * gap with the highest index.

 *

 * This function may be called under the rcu_read_lock.  However, this will

 * not atomically search a snapshot of the cache at a single point in time.

 * For example, if a gap is created at index 10, then subsequently a gap is

 * created at index 5, page_cache_prev_miss() covering both indices may

 * return 5 if called under the rcu_read_lock.

 *

 * Return: The index of the gap if found, otherwise an index outside the

 * range specified (in which case 'index - return >= max_scan' will be true).

 * In the rare case of wrap-around, ULONG_MAX will be returned.

 */

pgoff_t page_cache_prev_miss(struct address_space *mapping,

			     pgoff_t index, unsigned long max_scan)

{

	unsigned long i;



	for (i = 0; i < max_scan; i++) {

		struct page *page;

	XA_STATE(xas, &mapping->i_pages, index);



		page = radix_tree_lookup(&mapping->i_pages, index);

		if (!page || xa_is_value(page))

	while (max_scan--) {

		void *entry = xas_prev(&xas);

		if (!entry || xa_is_value(entry))

			break;

		index--;

		if (index == ULONG_MAX)

		if (xas.xa_index == ULONG_MAX)

			break;

	}



	return index;

	return xas.xa_index;

}

EXPORT_SYMBOL(page_cache_prev_hole);

EXPORT_SYMBOL(page_cache_prev_miss);



/**

 * find_get_entry - find and get a page cache entry

mm/readahead.c

+2 −2
Original line number Diff line number Diff line
@@ -336,7 +336,7 @@ static pgoff_t count_history_pages(struct address_space *mapping, 
	pgoff_t head;



	rcu_read_lock();

	head = page_cache_prev_hole(mapping, offset - 1, max);

	head = page_cache_prev_miss(mapping, offset - 1, max);

	rcu_read_unlock();



	return offset - 1 - head;
@@ -425,7 +425,7 @@ ondemand_readahead(struct address_space *mapping, 
		pgoff_t start;



		rcu_read_lock();

		start = page_cache_next_hole(mapping, offset + 1, max_pages);

		start = page_cache_next_miss(mapping, offset + 1, max_pages);

		rcu_read_unlock();



		if (!start || start - offset > max_pages)