dio: zero struct dio with kzalloc instead of manually
This patch uses kzalloc to zero all of struct dio rather than manually
trying to track which fields we rely on being zero. It passed aio+dio
stress testing and some bug regression testing on ext3.
This patch was introduced by Linus in the conversation that lead up to
Badari's minimal fix to manually zero .map_bh.b_state in commit:
6a648fa72161d1f6468dabd96c5d3c0db04f598a
It makes the code a bit smaller. Maybe a couple fewer cachelines to
load, if we're lucky:
text data bss dec hex filename
3285925 568506 1304616 5159047 4eb887 vmlinux
3285797 568506 1304616 5158919 4eb807 vmlinux.patched
I was unable to measure a stable difference in the number of cpu cycles
spent in blockdev_direct_IO() when pushing aio+dio 256K reads at
~340MB/s.
So the resulting intent of the patch isn't a performance gain but to
avoid exposing ourselves to the risk of finding another field like
.map_bh.b_state where we rely on zeroing but don't enforce it in the
code.
Signed-off-by: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 6874785..901dc55 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -958,36 +958,22 @@
ssize_t ret2;
size_t bytes;
- dio->bio = NULL;
dio->inode = inode;
dio->rw = rw;
dio->blkbits = blkbits;
dio->blkfactor = inode->i_blkbits - blkbits;
- dio->start_zero_done = 0;
- dio->size = 0;
dio->block_in_file = offset >> blkbits;
- dio->blocks_available = 0;
- dio->cur_page = NULL;
- dio->boundary = 0;
- dio->reap_counter = 0;
dio->get_block = get_block;
dio->end_io = end_io;
- dio->map_bh.b_private = NULL;
- dio->map_bh.b_state = 0;
dio->final_block_in_bio = -1;
dio->next_block_for_io = -1;
- dio->page_errors = 0;
- dio->io_error = 0;
- dio->result = 0;
dio->iocb = iocb;
dio->i_size = i_size_read(inode);
spin_lock_init(&dio->bio_lock);
dio->refcount = 1;
- dio->bio_list = NULL;
- dio->waiter = NULL;
/*
* In case of non-aligned buffers, we may need 2 more
@@ -995,8 +981,6 @@
*/
if (unlikely(dio->blkfactor))
dio->pages_in_io = 2;
- else
- dio->pages_in_io = 0;
for (seg = 0; seg < nr_segs; seg++) {
user_addr = (unsigned long)iov[seg].iov_base;
@@ -1184,7 +1168,7 @@
}
}
- dio = kmalloc(sizeof(*dio), GFP_KERNEL);
+ dio = kzalloc(sizeof(*dio), GFP_KERNEL);
retval = -ENOMEM;
if (!dio)
goto out;