[061/181] mm: add find_lock_head

Commit Message

Andrew Morton Oct. 13, 2020, 11:51 p.m. UTC

From: "Matthew Wilcox (Oracle)" <[e-mail]>
Subject: mm: add find_lock_head

Add a new FGP_HEAD flag which avoids calling find_subpage() and add a
convenience wrapper for it.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Cc: Huang Ying <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Cc: William Kucharski <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/pagemap.h |   32 ++++++++++++++++++++++++++------
 mm/filemap.c            |    9 ++++++---
 2 files changed, 32 insertions(+), 9 deletions(-)

Patch

--- a/include/linux/pagemap.h~mm-add-find_lock_head
+++ a/include/linux/pagemap.h
@@ -279,6 +279,7 @@  pgoff_t page_cache_prev_miss(struct addr
 #define FGP_NOFS		0x00000010
 #define FGP_NOWAIT		0x00000020
 #define FGP_FOR_MMAP		0x00000040
+#define FGP_HEAD		0x00000080
 
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
 		int fgp_flags, gfp_t cache_gfp_mask);
@@ -310,18 +311,37 @@  static inline struct page *find_get_page
  * @mapping: the address_space to search
  * @offset: the page index
  *
- * Looks up the page cache slot at @mapping & @offset.  If there is a
+ * Looks up the page cache entry at @mapping & @offset.  If there is a
  * page cache page, it is returned locked and with an increased
  * refcount.
  *
- * Otherwise, %NULL is returned.
- *
- * find_lock_page() may sleep.
+ * Context: May sleep.
+ * Return: A struct page or %NULL if there is no page in the cache for this
+ * index.
  */
 static inline struct page *find_lock_page(struct address_space *mapping,
-					pgoff_t offset)
+					pgoff_t index)
+{
+	return pagecache_get_page(mapping, index, FGP_LOCK, 0);
+}
+
+/**
+ * find_lock_head - Locate, pin and lock a pagecache page.
+ * @mapping: The address_space to search.
+ * @offset: The page index.
+ *
+ * Looks up the page cache entry at @mapping & @offset.  If there is a
+ * page cache page, its head page is returned locked and with an increased
+ * refcount.
+ *
+ * Context: May sleep.
+ * Return: A struct page which is !PageTail, or %NULL if there is no page
+ * in the cache for this index.
+ */
+static inline struct page *find_lock_head(struct address_space *mapping,
+					pgoff_t index)
 {
-	return pagecache_get_page(mapping, offset, FGP_LOCK, 0);
+	return pagecache_get_page(mapping, index, FGP_LOCK | FGP_HEAD, 0);
 }
 
 /**
--- a/mm/filemap.c~mm-add-find_lock_head
+++ a/mm/filemap.c
@@ -1737,6 +1737,8 @@  repeat:
  *
  * * %FGP_ACCESSED - The page will be marked accessed.
  * * %FGP_LOCK - The page is returned locked.
+ * * %FGP_HEAD - If the page is present and a THP, return the head page
+ *   rather than the exact page specified by the index.
  * * %FGP_CREAT - If no page is present then a new page is allocated using
  *   @gfp_mask and added to the page cache and the VM's LRU list.
  *   The page is returned locked and with an increased refcount.
@@ -1765,7 +1767,6 @@  repeat:
 		page = NULL;
 	if (!page)
 		goto no_page;
-	page = find_subpage(page, index);
 
 	if (fgp_flags & FGP_LOCK) {
 		if (fgp_flags & FGP_NOWAIT) {
@@ -1778,12 +1779,12 @@  repeat:
 		}
 
 		/* Has the page been truncated? */
-		if (unlikely(compound_head(page)->mapping != mapping)) {
+		if (unlikely(page->mapping != mapping)) {
 			unlock_page(page);
 			put_page(page);
 			goto repeat;
 		}
-		VM_BUG_ON_PAGE(page->index != index, page);
+		VM_BUG_ON_PAGE(!thp_contains(page, index), page);
 	}
 
 	if (fgp_flags & FGP_ACCESSED)
@@ -1793,6 +1794,8 @@  repeat:
 		if (page_is_idle(page))
 			clear_page_idle(page);
 	}
+	if (!(fgp_flags & FGP_HEAD))
+		page = find_subpage(page, index);
 
 no_page:
 	if (!page && (fgp_flags & FGP_CREAT)) {