[PATCH 7/8] mm: Return head page from find_lock_entry

Matthew Wilcox (Oracle)
2020-08-19T18:48:49Z

Convert the one caller of find_lock_entry() to cope with a head page
being returned instead of the subpage for the index.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 12 ++++++++++++
mm/filemap.c | 25 +++++++++++--------------
mm/shmem.c | 15 ++++++++-------
3 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 8261c64f592d..de8f3758ceaa 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -371,6 +371,18 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
mapping_gfp_mask(mapping));
}

+/*
+ * Is this index for one of the subpages of this page?
+ * This should always be called for a locked, non-hugetlbfs page.
+ */
+static inline bool thp_valid_index(struct page *head, pgoff_t index)
+{
+ VM_BUG_ON_PAGE(PageHuge(head), head);
+ VM_BUG_ON_PAGE(!PageLocked(head), head);
+
+ return head->index == (index & ~(thp_nr_pages(head) - 1));
+}
+
/*
* Given the page we found in the page cache, return the page corresponding
* to this index in the file
diff --git a/mm/filemap.c b/mm/filemap.c
index 5a87e1bdddd6..6594baae7cd2 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1594,37 +1594,34 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
}

/**
- * find_lock_entry - locate, pin and lock a page cache entry
- * @mapping: the address_space to search
- * @offset: the page cache index
+ * find_lock_entry - Locate and lock a page cache entry.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
*
- * Looks up the page cache slot at @mapping & @offset. If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
+ * Looks up the page at @mapping & @index. If there is a page in the
+ * cache, the head page is returned locked and with an increased refcount.
*
* If the slot holds a shadow entry of a previously evicted page, or a
* swap entry from shmem/tmpfs, it is returned.
*
- * find_lock_entry() may sleep.
- *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * Context: May sleep.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
*/
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
{
struct page *page;

repeat:
- page = find_get_entry(mapping, offset);
+ page = find_get_entry(mapping, index);
if (page && !xa_is_value(page)) {
lock_page(page);
/* Has the page been truncated? */
- if (unlikely(page_mapping(page) != mapping)) {
+ if (unlikely(page->mapping != mapping)) {
unlock_page(page);
put_page(page);
goto repeat;
}
- page = find_subpage(page, offset);
- VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
+ VM_BUG_ON_PAGE(!thp_valid_index(page, index), page);
}
return page;
}
diff --git a/mm/shmem.c b/mm/shmem.c
index 271548ca20f3..bbb43e9d35df 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1834,8 +1834,9 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
page = NULL;
}
if (page || sgp == SGP_READ) {
- *pagep = page;
- return 0;
+ if (page && PageTransHuge(page))
+ hindex = round_down(index, HPAGE_PMD_NR);
+ goto out;
}

/*
@@ -1961,14 +1962,13 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
* it now, lest undo on failure cancel our earlier guarantee.
*/
if (sgp != SGP_WRITE && !PageUptodate(page)) {
- struct page *head = compound_head(page);
int i;

- for (i = 0; i < compound_nr(head); i++) {
- clear_highpage(head + i);
- flush_dcache_page(head + i);
+ for (i = 0; i < compound_nr(page); i++) {
+ clear_highpage(page + i);
+ flush_dcache_page(page + i);
}
- SetPageUptodate(head);
+ SetPageUptodate(page);
}

/* Perhaps the file has been truncated since we checked */
@@ -1984,6 +1984,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
error = -EINVAL;
goto unlock;
}
+out:
*pagep = page + index - hindex;
return 0;

--
2.28.0