linux-kernel - [PATCH v6 04/51] mm: Move PageDoubleMap bit

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Message-Id: <20200610201345.13273-5-willy@infradead.org>
Date:   Wed, 10 Jun 2020 13:12:58 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 04/51] mm: Move PageDoubleMap bit

From: "Matthew Wilcox (Oracle)" <willy@...radead.org>

PG_private_2 is defined as being PF_ANY (applicable to tail pages
as well as regular & head pages).  That means that the first tail
page of a double-map page will appear to have Private2 set.  Use the
Workingset bit instead which is defined as PF_HEAD so any attempt to
access the Workingset bit on a tail page will redirect to the head page's
Workingset bit.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 include/linux/page-flags.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 222f6f7b2bb3..de6e0696f55c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -164,7 +164,7 @@ enum pageflags {
 	PG_slob_free = PG_private,
 
 	/* Compound pages. Stored in first tail page's flags */
-	PG_double_map = PG_private_2,
+	PG_double_map = PG_workingset,
 
 	/* non-lru isolated movable page */
 	PG_isolated = PG_reclaim,
-- 
2.26.2