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    Subject[PATCHv6 13/22] mm, vfs: introduce i_split_sem
    Date
    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@linux.intel.com>
    ---
    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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