From ffbd517d5a8c8e93ddd11046434fb029f3df73aa Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Mon, 20 Apr 2009 15:50:09 -0400 Subject: Btrfs: use WRITE_SYNC for synchronous writes Part of reducing fsync/O_SYNC/O_DIRECT latencies is using WRITE_SYNC for writes we plan on waiting on in the near future. This patch mirrors recent changes in other filesystems and the generic code to use WRITE_SYNC when WB_SYNC_ALL is passed and to use WRITE_SYNC for other latency critical writes. Btrfs uses async worker threads for checksumming before the write is done, and then again to actually submit the bios. The bio submission code just runs a per-device list of bios that need to be sent down the pipe. This list is split into low priority and high priority lists so the WRITE_SYNC IO happens first. Signed-off-by: Chris Mason --- fs/btrfs/extent_io.c | 44 ++++++++++++++++++++++++++++++-------------- 1 file changed, 30 insertions(+), 14 deletions(-) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index eb2bee8b7fb..483b6727aaa 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -50,7 +50,10 @@ struct extent_page_data { /* tells writepage not to lock the state bits for this range * it still does the unlocking */ - int extent_locked; + unsigned int extent_locked:1; + + /* tells the submit_bio code to use a WRITE_SYNC */ + unsigned int sync_io:1; }; int __init extent_io_init(void) @@ -2136,8 +2139,14 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, u64 delalloc_end; int page_started; int compressed; + int write_flags; unsigned long nr_written = 0; + if (wbc->sync_mode == WB_SYNC_ALL) + write_flags = WRITE_SYNC_PLUG; + else + write_flags = WRITE; + WARN_ON(!PageLocked(page)); pg_offset = i_size & (PAGE_CACHE_SIZE - 1); if (page->index > end_index || @@ -2314,9 +2323,9 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, (unsigned long long)end); } - ret = submit_extent_page(WRITE, tree, page, sector, - iosize, pg_offset, bdev, - &epd->bio, max_nr, + ret = submit_extent_page(write_flags, tree, page, + sector, iosize, pg_offset, + bdev, &epd->bio, max_nr, end_bio_extent_writepage, 0, 0, 0); if (ret) @@ -2460,15 +2469,23 @@ retry: return ret; } -static noinline void flush_write_bio(void *data) +static void flush_epd_write_bio(struct extent_page_data *epd) { - struct extent_page_data *epd = data; if (epd->bio) { - submit_one_bio(WRITE, epd->bio, 0, 0); + if (epd->sync_io) + submit_one_bio(WRITE_SYNC, epd->bio, 0, 0); + else + submit_one_bio(WRITE, epd->bio, 0, 0); epd->bio = NULL; } } +static noinline void flush_write_bio(void *data) +{ + struct extent_page_data *epd = data; + flush_epd_write_bio(epd); +} + int extent_write_full_page(struct extent_io_tree *tree, struct page *page, get_extent_t *get_extent, struct writeback_control *wbc) @@ -2480,6 +2497,7 @@ int extent_write_full_page(struct extent_io_tree *tree, struct page *page, .tree = tree, .get_extent = get_extent, .extent_locked = 0, + .sync_io = wbc->sync_mode == WB_SYNC_ALL, }; struct writeback_control wbc_writepages = { .bdi = wbc->bdi, @@ -2490,13 +2508,11 @@ int extent_write_full_page(struct extent_io_tree *tree, struct page *page, .range_end = (loff_t)-1, }; - ret = __extent_writepage(page, wbc, &epd); extent_write_cache_pages(tree, mapping, &wbc_writepages, __extent_writepage, &epd, flush_write_bio); - if (epd.bio) - submit_one_bio(WRITE, epd.bio, 0, 0); + flush_epd_write_bio(&epd); return ret; } @@ -2515,6 +2531,7 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode, .tree = tree, .get_extent = get_extent, .extent_locked = 1, + .sync_io = mode == WB_SYNC_ALL, }; struct writeback_control wbc_writepages = { .bdi = inode->i_mapping->backing_dev_info, @@ -2540,8 +2557,7 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode, start += PAGE_CACHE_SIZE; } - if (epd.bio) - submit_one_bio(WRITE, epd.bio, 0, 0); + flush_epd_write_bio(&epd); return ret; } @@ -2556,13 +2572,13 @@ int extent_writepages(struct extent_io_tree *tree, .tree = tree, .get_extent = get_extent, .extent_locked = 0, + .sync_io = wbc->sync_mode == WB_SYNC_ALL, }; ret = extent_write_cache_pages(tree, mapping, wbc, __extent_writepage, &epd, flush_write_bio); - if (epd.bio) - submit_one_bio(WRITE, epd.bio, 0, 0); + flush_epd_write_bio(&epd); return ret; } -- cgit From d313d7a31a752c88f7288692bd98e66d0789779b Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Mon, 20 Apr 2009 15:50:09 -0400 Subject: Btrfs: add a priority queue to the async thread helpers Btrfs is using WRITE_SYNC_PLUG to send down synchronous IOs with a higher priority. But, the checksumming helper threads prevent it from being fully effective. There are two problems. First, a big queue of pending checksumming will delay the synchronous IO behind other lower priority writes. Second, the checksumming uses an ordered async work queue. The ordering makes sure that IOs are sent to the block layer in the same order they are sent to the checksumming threads. Usually this gives us less seeky IO. But, when we start mixing IO priorities, the lower priority IO can delay the higher priority IO. This patch solves both problems by adding a high priority list to the async helper threads, and a new btrfs_set_work_high_prio(), which is used to make put a new async work item onto the higher priority list. The ordering is still done on high priority IO, but all of the high priority bios are ordered separately from the low priority bios. This ordering is purely an IO optimization, it is not involved in data or metadata integrity. Signed-off-by: Chris Mason --- fs/btrfs/extent_io.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 483b6727aaa..5d66cb27e42 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -2501,7 +2501,7 @@ int extent_write_full_page(struct extent_io_tree *tree, struct page *page, }; struct writeback_control wbc_writepages = { .bdi = wbc->bdi, - .sync_mode = WB_SYNC_NONE, + .sync_mode = wbc->sync_mode, .older_than_this = NULL, .nr_to_write = 64, .range_start = page_offset(page) + PAGE_CACHE_SIZE, -- cgit From 11c8349b4eb68f2b04cd8ece577377e6c0e5dd4b Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Mon, 20 Apr 2009 15:50:09 -0400 Subject: Btrfs: fix oops on page->mapping->host during writepage The extent_io writepage call updates the writepage index in the inode as it makes progress. But, it was doing the update after unlocking the page, which isn't legal because page->mapping can't be trusted once the page is unlocked. This lead to an oops, especially common with compression turned on. The fix here is to update the writeback index before unlocking the page. Signed-off-by: Chris Mason --- fs/btrfs/extent_io.c | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 5d66cb27e42..05a1c42e25b 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -2104,6 +2104,16 @@ int extent_read_full_page(struct extent_io_tree *tree, struct page *page, return ret; } +static noinline void update_nr_written(struct page *page, + struct writeback_control *wbc, + unsigned long nr_written) +{ + wbc->nr_to_write -= nr_written; + if (wbc->range_cyclic || (wbc->nr_to_write > 0 && + wbc->range_start == 0 && wbc->range_end == LLONG_MAX)) + page->mapping->writeback_index = page->index + nr_written; +} + /* * the writepage semantics are similar to regular writepage. extent * records are inserted to lock ranges in the tree, and as dirty areas @@ -2173,6 +2183,12 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, delalloc_end = 0; page_started = 0; if (!epd->extent_locked) { + /* + * make sure the wbc mapping index is at least updated + * to this page. + */ + update_nr_written(page, wbc, 0); + while (delalloc_end < page_end) { nr_delalloc = find_lock_delalloc_range(inode, tree, page, @@ -2194,7 +2210,13 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, */ if (page_started) { ret = 0; - goto update_nr_written; + /* + * we've unlocked the page, so we can't update + * the mapping's writeback index, just update + * nr_to_write. + */ + wbc->nr_to_write -= nr_written; + goto done_unlocked; } } lock_extent(tree, start, page_end, GFP_NOFS); @@ -2207,13 +2229,18 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, if (ret == -EAGAIN) { unlock_extent(tree, start, page_end, GFP_NOFS); redirty_page_for_writepage(wbc, page); + update_nr_written(page, wbc, nr_written); unlock_page(page); ret = 0; - goto update_nr_written; + goto done_unlocked; } } - nr_written++; + /* + * we don't want to touch the inode after unlocking the page, + * so we update the mapping writeback index now + */ + update_nr_written(page, wbc, nr_written + 1); end = page_end; if (test_range_bit(tree, start, page_end, EXTENT_DELALLOC, 0)) @@ -2345,11 +2372,8 @@ done: unlock_extent(tree, unlock_start, page_end, GFP_NOFS); unlock_page(page); -update_nr_written: - wbc->nr_to_write -= nr_written; - if (wbc->range_cyclic || (wbc->nr_to_write > 0 && - wbc->range_start == 0 && wbc->range_end == LLONG_MAX)) - page->mapping->writeback_index = page->index + nr_written; +done_unlocked: + return 0; } -- cgit