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radix-tree: use iterators in find_get_pages* functions 

Replace radix_tree_gang_lookup_slot() and
radix_tree_gang_lookup_tag_slot() in page-cache lookup functions with
brand-new radix-tree direct iterating.  This avoids the double-scanning
and pointer copying.

Iterator don't stop after nr_pages page-get fails in a row, it continue
lookup till the radix-tree end.  Thus we can safely remove these restart
conditions.

Unfortunately, old implementation didn't forbid nr_pages == 0, this corner
case does not fit into new code, so the patch adds an extra check at the
beginning.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Tested-by: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov 2012-03-28 14:42:54 -07:00 committed by Linus Torvalds
parent cebbd29e1c
commit 0fc9d10403
1 changed files with 38 additions and 48 deletions
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86
mm/filemap.c
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@ -813,20 +813,19 @@ EXPORT_SYMBOL(find_or_create_page);
unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
unsigned int nr_pages, struct page **pages)
{
unsigned int i;
unsigned int ret;
unsigned int nr_found, nr_skip;
struct radix_tree_iter iter;
void **slot;
unsigned ret = 0;
if (unlikely(!nr_pages))
return 0;
rcu_read_lock();
restart:
nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
(void ***)pages, NULL, start, nr_pages);
ret = 0;
nr_skip = 0;
for (i = 0; i < nr_found; i++) {
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
struct page *page;
repeat:
page = radix_tree_deref_slot((void **)pages[i]);
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
continue;
@ -837,7 +836,7 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
* when entry at index 0 moves out of or back
* to root: none yet gotten, safe to restart.
*/
WARN_ON(start | i);
WARN_ON(iter.index);
goto restart;
}
/*
@ -845,7 +844,6 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
* here as an exceptional entry: so skip over it -
* we only reach this from invalidate_mapping_pages().
*/
nr_skip++;
continue;
}
@ -853,21 +851,16 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
goto repeat;
/* Has the page moved? */
if (unlikely(page != *((void **)pages[i]))) {
if (unlikely(page != *slot)) {
page_cache_release(page);
goto repeat;
}
pages[ret] = page;
ret++;
if (++ret == nr_pages)
break;
}
/*
* If all entries were removed before we could secure them,
* try again, because callers stop trying once 0 is returned.
*/
if (unlikely(!ret && nr_found > nr_skip))
goto restart;
rcu_read_unlock();
return ret;
}
@ -887,21 +880,22 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
unsigned int nr_pages, struct page **pages)
{
unsigned int i;
unsigned int ret;
unsigned int nr_found;
struct radix_tree_iter iter;
void **slot;
unsigned int ret = 0;
if (unlikely(!nr_pages))
return 0;
rcu_read_lock();
restart:
nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
(void ***)pages, NULL, index, nr_pages);
ret = 0;
for (i = 0; i < nr_found; i++) {
radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
struct page *page;
repeat:
page = radix_tree_deref_slot((void **)pages[i]);
page = radix_tree_deref_slot(slot);
/* The hole, there no reason to continue */
if (unlikely(!page))
continue;
break;
if (radix_tree_exception(page)) {
if (radix_tree_deref_retry(page)) {
@ -924,7 +918,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
goto repeat;
/* Has the page moved? */
if (unlikely(page != *((void **)pages[i]))) {
if (unlikely(page != *slot)) {
page_cache_release(page);
goto repeat;
}
@ -934,14 +928,14 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
* otherwise we can get both false positives and false
* negatives, which is just confusing to the caller.
*/
if (page->mapping == NULL || page->index != index) {
if (page->mapping == NULL || page->index != iter.index) {
page_cache_release(page);
break;
}
pages[ret] = page;
ret++;
index++;
if (++ret == nr_pages)
break;
}
rcu_read_unlock();
return ret;
@ -962,19 +956,20 @@ EXPORT_SYMBOL(find_get_pages_contig);
unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
int tag, unsigned int nr_pages, struct page **pages)
{
unsigned int i;
unsigned int ret;
unsigned int nr_found;
struct radix_tree_iter iter;
void **slot;
unsigned ret = 0;
if (unlikely(!nr_pages))
return 0;
rcu_read_lock();
restart:
nr_found = radix_tree_gang_lookup_tag_slot(&mapping->page_tree,
(void ***)pages, *index, nr_pages, tag);
ret = 0;
for (i = 0; i < nr_found; i++) {
radix_tree_for_each_tagged(slot, &mapping->page_tree,
&iter, *index, tag) {
struct page *page;
repeat:
page = radix_tree_deref_slot((void **)pages[i]);
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
continue;
@ -998,21 +993,16 @@ unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
goto repeat;
/* Has the page moved? */
if (unlikely(page != *((void **)pages[i]))) {
if (unlikely(page != *slot)) {
page_cache_release(page);
goto repeat;
}
pages[ret] = page;
ret++;
if (++ret == nr_pages)
break;
}
/*
* If all entries were removed before we could secure them,
* try again, because callers stop trying once 0 is returned.
*/
if (unlikely(!ret && nr_found))
goto restart;
rcu_read_unlock();
if (ret)