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 <[email protected]>
---
fs/direct-io.c | 18 +-----------------
1 files changed, 1 insertions(+), 17 deletions(-)
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 1d0bdf0..be86702 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -958,36 +958,22 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
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 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
*/
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;
@@ -1194,7 +1178,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
}
}
- dio = kmalloc(sizeof(*dio), GFP_KERNEL);
+ dio = kzalloc(sizeof(*dio), GFP_KERNEL);
retval = -ENOMEM;
if (!dio)
goto out;
-
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