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

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
......@@ -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();
}
......
......@@ -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
......
......@@ -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.
* 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_hole(struct address_space *mapping,
pgoff_t page_cache_next_miss(struct address_space *mapping,
pgoff_t index, unsigned long max_scan)
{
unsigned long i;
XA_STATE(xas, &mapping->i_pages, index);
for (i = 0; i < max_scan; i++) {
struct page *page;
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.
* 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_hole(struct address_space *mapping,
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
......
......@@ -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)
......
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