[PATCH] fs: reorder some 'struct inode' fields to speedup i_size manipulations

On 32bits SMP platforms, 64bits i_size is protected by a seqcount
(i_size_seqcount).

When i_size is read or written, i_size_seqcount is read/written as well, so
it make sense to group these two fields together in the same cache line.

This patch moves i_size_seqcount next to i_size, and also moves i_version
to let offsetof(struct inode, i_size) being 0x40 instead of 0x3c (for
32bits platforms).

For 64 bits platforms, i_size_seqcount doesnt exist, and the move of a
'long i_version' should not introduce a new hole because of padding.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index d791bae9de9c8d23d7f1d04d222f132b880ad1ba..3a1927e516d041ad4b7e0197f729cd81b2043acd 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -548,12 +548,15 @@ struct inode {
        uid_t                   i_uid;
        gid_t                   i_gid;
        dev_t                   i_rdev;
+       unsigned long           i_version;
        loff_t                  i_size;
+#ifdef __NEED_I_SIZE_ORDERED
+       seqcount_t              i_size_seqcount;
+#endif
        struct timespec         i_atime;
        struct timespec         i_mtime;
        struct timespec         i_ctime;
        unsigned int            i_blkbits;
-       unsigned long           i_version;
        blkcnt_t                i_blocks;
        unsigned short          i_bytes;
        spinlock_t              i_lock; /* i_blocks, i_bytes, maybe i_size */
@@ -598,9 +601,6 @@ struct inode {
        void                    *i_security;
 #endif
        void                    *i_private; /* fs or device private pointer */
-#ifdef __NEED_I_SIZE_ORDERED
-       seqcount_t              i_size_seqcount;
-#endif
 };
 
 /*