[PATCHv6 13/22] mm, vfs: introduce i_split_sem

[Kirill A. Shutemov]

i_split_sem taken on read will protect hugepages in inode's pagecache
against splitting.

i_split_sem will be taken on write during splitting.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 fs/inode.c              |  3 +++
 include/linux/fs.h      |  3 +++
 include/linux/huge_mm.h | 10 ++++++++++
 3 files changed, 16 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index b33ba8e021..ea06e378c6 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -162,6 +162,9 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 
 	atomic_set(&inode->i_dio_count, 0);
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
+	init_rwsem(&inode->i_split_sem);
+#endif
 	mapping->a_ops = &empty_aops;
 	mapping->host = inode;
 	mapping->flags = 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3f40547ba1..26801f0bb1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -610,6 +610,9 @@ struct inode {
 	atomic_t		i_readcount; /* struct files open RO */
 #endif
 	void			*i_private; /* fs or device private pointer */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
+	struct rw_semaphore	i_split_sem;
+#endif
 };
 
 static inline int inode_unhashed(struct inode *inode)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 3700ada4d2..ce9fcae8ef 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -241,12 +241,22 @@ static inline int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_str
 #define HPAGE_CACHE_NR         (1L << HPAGE_CACHE_ORDER)
 #define HPAGE_CACHE_INDEX_MASK (HPAGE_CACHE_NR - 1)
 
+#define i_split_down_read(inode) down_read(&inode->i_split_sem)
+#define i_split_up_read(inode) up_read(&inode->i_split_sem)
+
 #else
 
 #define HPAGE_CACHE_ORDER      ({ BUILD_BUG(); 0; })
 #define HPAGE_CACHE_NR         ({ BUILD_BUG(); 0; })
 #define HPAGE_CACHE_INDEX_MASK ({ BUILD_BUG(); 0; })
 
+static inline void i_split_down_read(struct inode *inode)
+{
+}
+
+static inline void i_split_up_read(struct inode *inode)
+{
+}
 #endif
 
 static inline bool transparent_hugepage_pagecache(void)
-- 
1.8.4.rc3

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