dio: zero struct dio with kzalloc instead of manually (848c4dd5) · Commits · 戴 / test

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: 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>

fs/direct-io.c

+1 −17

Original line number	Diff line number	Diff line
		@@ -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;

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