xfs: increase readdir buffer size
While doing some testing of readdir perf a while back,
I noticed that the buffer size we're using internally is
smaller than what glibc gives us by default. Upping this
size helped a bit, and seems safe.
glibc's __alloc_dir() does:
const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
? sizeof (struct dirent64) : 4 * BUFSIZ);
const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
? sizeof (struct dirent64) : BUFSIZ);
size_t allocation = default_allocation;
#ifdef _STATBUF_ST_BLKSIZE
if (statp != NULL && default_allocation < statp->st_blksize)
allocation = statp->st_blksize;
#endif
and
#define _G_BUFSIZ 8192
#define _IO_BUFSIZ _G_BUFSIZ
# define BUFSIZ _IO_BUFSIZ
so the default buffer is 4 * 8192 = 32768
(except in the unlikely case of blocks > 32k....)
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index e4caeb2..3805ada 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -203,9 +203,9 @@
*
* Try to give it an estimate that's good enough, maybe at some
* point we can change the ->readdir prototype to include the
- * buffer size.
+ * buffer size. For now we use the current glibc buffer size.
*/
- bufsize = (size_t)min_t(loff_t, PAGE_SIZE, ip->i_d.di_size);
+ bufsize = (size_t)min_t(loff_t, 32768, ip->i_d.di_size);
error = xfs_readdir(ip, dirent, bufsize,
(xfs_off_t *)&filp->f_pos, filldir);