linux-kernel - [PATCH 8/8] mm: Hoist find_subpage call further up in pagecache_get

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Date:   Wed, 19 Aug 2020 19:48:50 +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 8/8] mm: Hoist find_subpage call further up in pagecache_get_page

This avoids a call to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 mm/filemap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 6594baae7cd2..8c354277108d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1667,7 +1667,6 @@ 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) {
@@ -1680,12 +1679,12 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 		}
 
 		/* 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_valid_index(page, index), page);
 	}
 
 	if (fgp_flags & FGP_ACCESSED)
@@ -1695,6 +1694,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 		if (page_is_idle(page))
 			clear_page_idle(page);
 	}
+	page = find_subpage(page, index);
 
 no_page:
 	if (!page && (fgp_flags & FGP_CREAT)) {
-- 
2.28.0