From d2c3f4f695edac4d75c1b3eb01a1d16072de63bb Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Wed, 19 Nov 2008 12:44:22 -0500 Subject: Btrfs: Avoid writeback stalls While building large bios in writepages, btrfs may end up waiting for other page writeback to finish if WB_SYNC_ALL is used. While it is waiting, the bio it is building has a number of pages with the writeback bit set and they aren't getting to the disk any time soon. This lowers the latencies of writeback in general by sending down the bio being built before waiting for other pages. The bio submission code tries to limit the total number of async bios in flight by waiting when we're over a certain number of async bios. But, the waits are happening while writepages is building bios, and this can easily lead to stalls and other problems for people calling wait_on_page_writeback. The current fix is to let the congestion tests take care of waiting. sync() and others make sure to drain the current async requests to make sure that everything that was pending when the sync was started really get to disk. The code would drain pending requests both before and after submitting a new request. But, if one of the requests is waiting for page writeback to finish, the draining waits might block that page writeback. This changes the draining code to only wait after submitting the bio being processed. Signed-off-by: Chris Mason --- fs/btrfs/inode.c | 7 ------- 1 file changed, 7 deletions(-) (limited to 'fs/btrfs/inode.c') diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 6854bf4..806caac 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -883,13 +883,6 @@ static int cow_file_range_async(struct inode *inode, struct page *locked_page, async_cow->work.ordered_free = async_cow_free; async_cow->work.flags = 0; - while(atomic_read(&root->fs_info->async_submit_draining) && - atomic_read(&root->fs_info->async_delalloc_pages)) { - wait_event(root->fs_info->async_submit_wait, - (atomic_read(&root->fs_info->async_delalloc_pages) - == 0)); - } - nr_pages = (cur_end - start + PAGE_CACHE_SIZE) >> PAGE_CACHE_SHIFT; atomic_add(nr_pages, &root->fs_info->async_delalloc_pages); -- cgit v1.1