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dio: zero struct dio with kzalloc instead of manually

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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:

  6a648fa721

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>
This commit is contained in:
Zach Brown 2007-08-20 17:12:01 -07:00 committed by Linus Torvalds
parent 38f061c571
commit 848c4dd515
1 changed files with 1 additions and 17 deletions
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18
fs/direct-io.c
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@ -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;
@ -1184,7 +1168,7 @@ __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;