linux-kernel - [PATCH 6/8] mm: Convert find_get

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Message-Id: <20200819184850.24779-7-willy@infradead.org>
Date:   Wed, 19 Aug 2020 19:48:48 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Matthew Auld <matthew.auld@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        intel-gfx@...ts.freedesktop.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 6/8] mm: Convert find_get_entry to return the head page

There are only three callers remaining of find_get_entry().
find_get_swap_page() is happy to get the head page instead of the subpage.
Add find_subpage() calls to find_lock_entry() and pagecache_get_page()
to avoid auditing all their callers.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 include/linux/pagemap.h |  4 ++--
 mm/filemap.c            | 13 +++++++------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 7de11dcd534d..8261c64f592d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -384,8 +384,8 @@ static inline struct page *find_subpage(struct page *head, pgoff_t index)
 	return head + (index & (thp_nr_pages(head) - 1));
 }
 
-struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
+struct page *find_get_entry(struct address_space *mapping, pgoff_t index);
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index);
 unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
 			  unsigned int nr_entries, struct page **entries,
 			  pgoff_t *indices);
diff --git a/mm/filemap.c b/mm/filemap.c
index 36067cf7f8c5..5a87e1bdddd6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1547,19 +1547,19 @@ EXPORT_SYMBOL(page_cache_prev_miss);
 /**
  * find_get_entry - find and get a page cache entry
  * @mapping: the address_space to search
- * @offset: the page cache index
+ * @index: The page cache index.
  *
  * Looks up the page cache slot at @mapping & @offset.  If there is a
- * page cache page, it is returned with an increased refcount.
+ * page cache page, the head page is returned 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.
  *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
  */
-struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
+struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
 {
-	XA_STATE(xas, &mapping->i_pages, offset);
+	XA_STATE(xas, &mapping->i_pages, index);
 	struct page *page;
 
 	rcu_read_lock();
@@ -1587,7 +1587,6 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
 		put_page(page);
 		goto repeat;
 	}
-	page = find_subpage(page, offset);
 out:
 	rcu_read_unlock();
 
@@ -1624,6 +1623,7 @@ struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
 			put_page(page);
 			goto repeat;
 		}
+		page = find_subpage(page, offset);
 		VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
 	}
 	return page;
@@ -1670,6 +1670,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 		page = NULL;
 	if (!page)
 		goto no_page;
+	page = find_subpage(page, index);
 
 	if (fgp_flags & FGP_LOCK) {
 		if (fgp_flags & FGP_NOWAIT) {
-- 
2.28.0