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From:   Matthew Wilcox <willy@infradead.org>
To:     linux-fsdevel@vger.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH v6 14/51] fs: Add a filesystem flag for THPs
Date:   Wed, 10 Jun 2020 13:13:08 -0700
Message-Id: <20200610201345.13273-15-willy@infradead.org>
In-Reply-To: <20200610201345.13273-1-willy@infradead.org>
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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

The page cache needs to know whether the filesystem supports THPs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/inode.c              | 2 ++
 include/linux/fs.h      | 1 +
 include/linux/pagemap.h | 6 ++++++
 mm/shmem.c              | 2 +-
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 72c4c347afb7..9d78c37b00b8 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -181,6 +181,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	mapping->a_ops = &empty_aops;
 	mapping->host = inode;
 	mapping->flags = 0;
+	if (sb->s_type->fs_flags & FS_THP_SUPPORT)
+		__set_bit(AS_THP_SUPPORT, &mapping->flags);
 	mapping->wb_err = 0;
 	atomic_set(&mapping->i_mmap_writable, 0);
 #ifdef CONFIG_READ_ONLY_THP_FOR_FS
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 19ef6c88c152..ac411a08f83c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2241,6 +2241,7 @@ struct file_system_type {
 #define FS_HAS_SUBTYPE		4
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
 #define FS_DISALLOW_NOTIFY_PERM	16	/* Disable fanotify permission events */
+#define FS_THP_SUPPORT		8192	/* Remove once all fs converted */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
 	int (*init_fs_context)(struct fs_context *);
 	const struct fs_parameter_spec *parameters;
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 484a36185bb5..8a45b572bcf1 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -29,6 +29,7 @@ enum mapping_flags {
 	AS_EXITING	= 4, 	/* final truncate in progress */
 	/* writeback related tags are not used */
 	AS_NO_WRITEBACK_TAGS = 5,
+	AS_THP_SUPPORT = 6,	/* THPs supported */
 };
 
 /**
@@ -119,6 +120,11 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
 	m->gfp_mask = mask;
 }
 
+static inline bool mapping_thp_support(struct address_space *mapping)
+{
+	return test_bit(AS_THP_SUPPORT, &mapping->flags);
+}
+
 void release_pages(struct page **pages, int nr);
 
 /*
diff --git a/mm/shmem.c b/mm/shmem.c
index a0dbe62f8042..a05d129a45e9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3854,7 +3854,7 @@ static struct file_system_type shmem_fs_type = {
 	.parameters	= shmem_fs_parameters,
 #endif
 	.kill_sb	= kill_litter_super,
-	.fs_flags	= FS_USERNS_MOUNT,
+	.fs_flags	= FS_USERNS_MOUNT | FS_THP_SUPPORT,
 };
 
 int __init shmem_init(void)
-- 
2.26.2