[PATCHv2 24/28] filemap: prepare find and delete operations for huge pages

From: Kirill A. Shutemov
Date: Thu Feb 11 2016 - 09:28:09 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 | 187 ++++++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 134 insertions(+), 53 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index ba8150d6dc33..d082ca524ba3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -110,43 +110,18 @@
* ->tasklist_lock (memory_failure, collect_procs_ao)
*/

-static void page_cache_tree_delete(struct address_space *mapping,
- struct page *page, void *shadow)
+static void __page_cache_tree_delete(struct address_space *mapping,
+ struct radix_tree_node *node, void **slot, unsigned long index,
+ void *shadow)
{
- struct radix_tree_node *node;
- unsigned long index;
- unsigned int offset;
unsigned int tag;
- void **slot;
-
- VM_BUG_ON(!PageLocked(page));

- __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
-
- if (shadow) {
- mapping->nrexceptional++;
- /*
- * Make sure the nrexceptional update is committed before
- * the nrpages update so that final truncate racing
- * with reclaim does not see both counters 0 at the
- * same time and miss a shadow entry.
- */
- smp_wmb();
- }
- mapping->nrpages--;
-
- if (!node) {
- /* Clear direct pointer tags in root node */
- mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
- radix_tree_replace_slot(slot, shadow);
- return;
- }
+ VM_BUG_ON(node == NULL);
+ VM_BUG_ON(*slot == NULL);

/* Clear tree tags for the removed page */
- index = page->index;
- offset = index & RADIX_TREE_MAP_MASK;
for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
- if (test_bit(offset, node->tags[tag]))
+ if (test_bit(index & RADIX_TREE_MAP_MASK, node->tags[tag]))
radix_tree_tag_clear(&mapping->page_tree, index, tag);
}

@@ -173,6 +148,54 @@ static void page_cache_tree_delete(struct address_space *mapping,
}
}

+static void page_cache_tree_delete(struct address_space *mapping,
+ struct page *page, void *shadow)
+{
+ struct radix_tree_node *node;
+ unsigned long index;
+ void **slot;
+ int i, nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
+
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(PageTail(page), page);
+
+ __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
+
+ if (shadow) {
+ mapping->nrexceptional += nr;
+ /*
+ * Make sure the nrexceptional update is committed before
+ * the nrpages update so that final truncate racing
+ * with reclaim does not see both counters 0 at the
+ * same time and miss a shadow entry.
+ */
+ smp_wmb();
+ }
+ mapping->nrpages -= nr;
+
+ if (!node) {
+ /* Clear direct pointer tags in root node */
+ mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
+ VM_BUG_ON(nr != 1);
+ radix_tree_replace_slot(slot, shadow);
+ return;
+ }
+
+ index = page->index;
+ VM_BUG_ON_PAGE(index & (nr - 1), page);
+ for (i = 0; i < nr; i++) {
+ /* Cross node border */
+ if (i && ((index + i) & RADIX_TREE_MAP_MASK) == 0) {
+ __radix_tree_lookup(&mapping->page_tree,
+ page->index + i, &node, &slot);
+ }
+
+ __page_cache_tree_delete(mapping, node,
+ slot + (i & RADIX_TREE_MAP_MASK), index + i,
+ shadow);
+ }
+}
+
/*
* Delete a page from the page cache and free it. Caller has to make
* sure the page is locked and that nobody else uses it - or that usage
@@ -181,6 +204,7 @@ 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);
/*
@@ -200,9 +224,10 @@ 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);
+ VM_BUG_ON_PAGE(PageTail(page), page);
VM_BUG_ON_PAGE(page_mapped(page), page);

/*
@@ -227,9 +252,8 @@ 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));
@@ -242,7 +266,13 @@ void delete_from_page_cache(struct page *page)

if (freepage)
freepage(page);
- page_cache_release(page);
+
+ if (PageTransHuge(page) && !PageHuge(page)) {
+ atomic_sub(HPAGE_PMD_NR, &page->_count);
+ VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
+ } else {
+ page_cache_release(page);
+ }
}
EXPORT_SYMBOL(delete_from_page_cache);

@@ -1035,7 +1065,7 @@ 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:
@@ -1055,9 +1085,17 @@ 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) {
+ page_cache_release(page);
+ goto repeat;
+ }
+
/*
* Has the page moved?
* This is part of the lockless pagecache protocol. See
@@ -1100,12 +1138,12 @@ 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);
page_cache_release(page);
goto repeat;
}
- VM_BUG_ON_PAGE(page->index != offset, page);
+ VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
}
return page;
}
@@ -1238,7 +1276,7 @@ unsigned find_get_entries(struct address_space *mapping,
rcu_read_lock();
restart:
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))
@@ -1253,8 +1291,16 @@ 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) {
+ page_cache_release(page);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
@@ -1300,7 +1346,7 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
rcu_read_lock();
restart:
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))
@@ -1324,9 +1370,16 @@ 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) {
+ page_cache_release(page);
+ goto repeat;
+ }
+
/* Has the page moved? */
if (unlikely(page != *slot)) {
page_cache_release(page);
@@ -1367,7 +1420,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
rcu_read_lock();
restart:
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 */
@@ -1391,8 +1444,14 @@ 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) {
+ page_cache_release(page);
+ goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
@@ -1405,7 +1464,7 @@ 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) {
page_cache_release(page);
break;
}
@@ -1444,7 +1503,7 @@ unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
restart:
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))
@@ -1473,8 +1532,15 @@ 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) {
+ page_cache_release(page);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
@@ -1523,7 +1589,7 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
restart:
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))
@@ -1545,9 +1611,17 @@ 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) {
+ page_cache_release(page);
+ goto repeat;
+ }
+
/* Has the page moved? */
if (unlikely(page != *slot)) {
page_cache_release(page);
@@ -2139,7 +2213,7 @@ 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,
@@ -2157,8 +2231,15 @@ 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) {
+ page_cache_release(page);
goto repeat;
+ }

/* Has the page moved? */
if (unlikely(page != *slot)) {
--
2.7.0

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