dio: use a slab cache for struct dio

A direct slab call is slightly faster than kmalloc and can be better
cached per CPU.  It also avoids rounding to the next kmalloc slab.

In addition this enforces cache line alignment for struct dio to avoid any
false sharing.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 2d07a69431ab77127ac86bd48c696ebe4d1a4d29..2443c48c43c7b7a0f3b7e1bfd19f64bee358b4c1 100644 (file)
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -140,7 +140,9 @@ struct dio {
         * wish that they not be zeroed.
         */
        struct page *pages[DIO_PAGES];  /* page buffer */
-};
+} ____cacheline_aligned_in_smp;
+
+static struct kmem_cache *dio_cache __read_mostly;
 
 static void __inode_dio_wait(struct inode *inode)
 {
@@ -330,7 +332,7 @@ static void dio_bio_end_aio(struct bio *bio, int error)
 
        if (remaining == 0) {
                dio_complete(dio, dio->iocb->ki_pos, 0, true);
-               kfree(dio);
+               kmem_cache_free(dio_cache, dio);
        }
 }
 
@@ -1174,7 +1176,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 
        if (ret2 == 0) {
                ret = dio_complete(dio, offset, ret, false);
-               kfree(dio);
+               kmem_cache_free(dio_cache, dio);
        } else
                BUG_ON(ret != -EIOCBQUEUED);
 
@@ -1250,7 +1252,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
        if (rw == READ && end == offset)
                return 0;
 
-       dio = kmalloc(sizeof(*dio), GFP_KERNEL);
+       dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
        retval = -ENOMEM;
        if (!dio)
                goto out;
@@ -1274,7 +1276,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
                                                              end - 1);
                        if (retval) {
                                mutex_unlock(&inode->i_mutex);
-                               kfree(dio);
+                               kmem_cache_free(dio_cache, dio);
                                goto out;
                        }
                }
@@ -1302,3 +1304,10 @@ out:
        return retval;
 }
 EXPORT_SYMBOL(__blockdev_direct_IO);
+
+static __init int dio_init(void)
+{
+       dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
+       return 0;
+}
+module_init(dio_init)