[PATCHv9-rebased2 24/37] filemap: prepare find and delete operations for huge pages

From: Kirill A. Shutemov
Date: Wed Jun 15 2016 - 16:15:28 EST

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For now, we would have HPAGE_PMD_NR entries in radix tree for every huge
page. That's suboptimal and it will be changed to use Matthew's
multi-order entries later.

'add' operation is not changed, because we don't need it to implement
hugetmpfs: shmem uses its own implementation.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
mm/filemap.c | 178 ++++++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 122 insertions(+), 56 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 1efd2994dccf..21508ea25717 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -114,14 +114,14 @@ static void page_cache_tree_delete(struct address_space *mapping,
struct page *page, void *shadow)
{
struct radix_tree_node *node;
+ int i, nr = PageHuge(page) ? 1 : hpage_nr_pages(page);

- VM_BUG_ON(!PageLocked(page));
-
- node = radix_tree_replace_clear_tags(&mapping->page_tree, page->index,
- shadow);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(PageTail(page), page);
+ VM_BUG_ON_PAGE(nr != 1 && shadow, page);

if (shadow) {
- mapping->nrexceptional++;
+ mapping->nrexceptional += nr;
/*
* Make sure the nrexceptional update is committed before
* the nrpages update so that final truncate racing
@@ -130,31 +130,38 @@ static void page_cache_tree_delete(struct address_space *mapping,
*/
smp_wmb();
}
- mapping->nrpages--;
-
- if (!node)
- return;
+ mapping->nrpages -= nr;

- workingset_node_pages_dec(node);
- if (shadow)
- workingset_node_shadows_inc(node);
- else
- if (__radix_tree_delete_node(&mapping->page_tree, node))
+ for (i = 0; i < nr; i++) {
+ node = radix_tree_replace_clear_tags(&mapping->page_tree,
+ page->index + i, shadow);
+ if (!node) {
+ VM_BUG_ON_PAGE(nr != 1, page);
return;
+ }

- /*
- * Track node that only contains shadow entries. DAX mappings contain
- * no shadow entries and may contain other exceptional entries so skip
- * those.
- *
- * Avoid acquiring the list_lru lock if already tracked. The
- * list_empty() test is safe as node->private_list is
- * protected by mapping->tree_lock.
- */
- if (!dax_mapping(mapping) && !workingset_node_pages(node) &&
- list_empty(&node->private_list)) {
- node->private_data = mapping;
- list_lru_add(&workingset_shadow_nodes, &node->private_list);
+ workingset_node_pages_dec(node);
+ if (shadow)
+ workingset_node_shadows_inc(node);
+ else
+ if (__radix_tree_delete_node(&mapping->page_tree, node))
+ continue;
+
+ /*
+ * Track node that only contains shadow entries. DAX mappings
+ * contain no shadow entries and may contain other exceptional
+ * entries so skip those.
+ *
+ * Avoid acquiring the list_lru lock if already tracked.
+ * The list_empty() test is safe as node->private_list is
+ * protected by mapping->tree_lock.
+ */
+ if (!dax_mapping(mapping) && !workingset_node_pages(node) &&
+ list_empty(&node->private_list)) {
+ node->private_data = mapping;
+ list_lru_add(&workingset_shadow_nodes,
+ &node->private_list);
+ }
}
}

@@ -166,6 +173,7 @@ static void page_cache_tree_delete(struct address_space *mapping,
void __delete_from_page_cache(struct page *page, void *shadow)
{
struct address_space *mapping = page->mapping;
+ int nr = hpage_nr_pages(page);

trace_mm_filemap_delete_from_page_cache(page);
/*
@@ -178,6 +186,7 @@ void __delete_from_page_cache(struct page *page, void *shadow)
else
cleancache_invalidate_page(mapping, page);

+ VM_BUG_ON_PAGE(PageTail(page), page);
VM_BUG_ON_PAGE(page_mapped(page), page);
if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
int mapcount;
@@ -209,9 +218,9 @@ void __delete_from_page_cache(struct page *page, void *shadow)

/* hugetlb pages do not participate in page cache accounting. */
if (!PageHuge(page))
- __dec_zone_page_state(page, NR_FILE_PAGES);
+ __mod_zone_page_state(page_zone(page), NR_FILE_PAGES, -nr);
if (PageSwapBacked(page))
- __dec_zone_page_state(page, NR_SHMEM);
+ __mod_zone_page_state(page_zone(page), NR_SHMEM, -nr);

/*
* At this point page must be either written or cleaned by truncate.
@@ -235,9 +244,8 @@ void __delete_from_page_cache(struct page *page, void *shadow)
*/
void delete_from_page_cache(struct page *page)
{
- struct address_space *mapping = page->mapping;
+ struct address_space *mapping = page_mapping(page);
unsigned long flags;
-
void (*freepage)(struct page *);

BUG_ON(!PageLocked(page));
@@ -250,7 +258,13 @@ void delete_from_page_cache(struct page *page)

if (freepage)
freepage(page);
- put_page(page);
+
+ if (PageTransHuge(page) && !PageHuge(page)) {
+ page_ref_sub(page, HPAGE_PMD_NR);
+ VM_BUG_ON_PAGE(page_count(page) <= 0, page);
+ } else {
+ put_page(page);
+ }
}
EXPORT_SYMBOL(delete_from_page_cache);

@@ -1053,7 +1067,7 @@ EXPORT_SYMBOL(page_cache_prev_hole);
struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
{
void **pagep;
- struct page *page;
+ struct page *head, *page;

rcu_read_lock();
repeat:
@@ -1073,8 +1087,16 @@ repeat:
*/
goto out;
}
- if (!page_cache_get_speculative(page))
+
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
+ goto repeat;
+
+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
goto repeat;
+ }

/*
* Has the page moved?
@@ -1082,7 +1104,7 @@ repeat:
* include/linux/pagemap.h for details.
*/
if (unlikely(page != *pagep)) {
- put_page(page);
+ put_page(head);
goto repeat;
}
}
@@ -1118,12 +1140,12 @@ repeat:
if (page && !radix_tree_exception(page)) {
lock_page(page);
/* Has the page been truncated? */
- if (unlikely(page->mapping != mapping)) {
+ if (unlikely(page_mapping(page) != mapping)) {
unlock_page(page);
put_page(page);
goto repeat;
}
- VM_BUG_ON_PAGE(page->index != offset, page);
+ VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
}
return page;
}
@@ -1255,7 +1277,7 @@ unsigned find_get_entries(struct address_space *mapping,

rcu_read_lock();
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
- struct page *page;
+ struct page *head, *page;
repeat:
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
@@ -1272,12 +1294,20 @@ repeat:
*/
goto export;
}
- if (!page_cache_get_speculative(page))
+
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
+ goto repeat;
+
+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}
export:
@@ -1318,7 +1348,7 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,

rcu_read_lock();
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
- struct page *page;
+ struct page *head, *page;
repeat:
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
@@ -1337,12 +1367,19 @@ repeat:
continue;
}

- if (!page_cache_get_speculative(page))
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
+ goto repeat;
+
+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}

@@ -1379,7 +1416,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,

rcu_read_lock();
radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
- struct page *page;
+ struct page *head, *page;
repeat:
page = radix_tree_deref_slot(slot);
/* The hole, there no reason to continue */
@@ -1399,12 +1436,19 @@ repeat:
break;
}

- if (!page_cache_get_speculative(page))
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
+ goto repeat;
+
+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}

@@ -1413,7 +1457,7 @@ repeat:
* otherwise we can get both false positives and false
* negatives, which is just confusing to the caller.
*/
- if (page->mapping == NULL || page->index != iter.index) {
+ if (page->mapping == NULL || page_to_pgoff(page) != iter.index) {
put_page(page);
break;
}
@@ -1451,7 +1495,7 @@ unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
rcu_read_lock();
radix_tree_for_each_tagged(slot, &mapping->page_tree,
&iter, *index, tag) {
- struct page *page;
+ struct page *head, *page;
repeat:
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
@@ -1476,12 +1520,19 @@ repeat:
continue;
}

- if (!page_cache_get_speculative(page))
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
goto repeat;

+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
+ goto repeat;
+ }
+
/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}

@@ -1525,7 +1576,7 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
rcu_read_lock();
radix_tree_for_each_tagged(slot, &mapping->page_tree,
&iter, start, tag) {
- struct page *page;
+ struct page *head, *page;
repeat:
page = radix_tree_deref_slot(slot);
if (unlikely(!page))
@@ -1543,12 +1594,20 @@ repeat:
*/
goto export;
}
- if (!page_cache_get_speculative(page))
+
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
goto repeat;

+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
+ goto repeat;
+ }
+
/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}
export:
@@ -2137,7 +2196,7 @@ void filemap_map_pages(struct fault_env *fe,
struct address_space *mapping = file->f_mapping;
pgoff_t last_pgoff = start_pgoff;
loff_t size;
- struct page *page;
+ struct page *head, *page;

rcu_read_lock();
radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
@@ -2156,12 +2215,19 @@ repeat:
goto next;
}

- if (!page_cache_get_speculative(page))
+ head = compound_head(page);
+ if (!page_cache_get_speculative(head))
goto repeat;

+ /* The page was split under us? */
+ if (compound_head(page) != head) {
+ put_page(head);
+ goto repeat;
+ }
+
/* Has the page moved? */
if (unlikely(page != *slot)) {
- put_page(page);
+ put_page(head);
goto repeat;
}

--
2.8.1

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