hello, On 05/19/2016 07:01 PM, Filipe Manana wrote:
Sorry, this WARNINGs was only triggered when I manually modify BTRFS_MAX_EXTENT_SIZE to 64 KB. For 128MB, because btrfs_dirty_pages() will not handle data range lager than 128MB, it will always be be involved in one outstanding extent, so the WARNINGs will not happen. See that _btrfs_buffered_write has a write limitation for every iteration(it seems 2MB).On Thu, May 19, 2016 at 11:49 AM, Wang Xiaoguang <wangxg.f...@cn.fujitsu.com> wrote:This issue was revealed by modifing BTRFS_MAX_EXTENT_SIZE(128MB) to 64KB, When modifing BTRFS_MAX_EXTENT_SIZE(128MB) to 64KB, fsstress test often gets these warnings from btrfs_destroy_inode(): WARN_ON(BTRFS_I(inode)->outstanding_extents); WARN_ON(BTRFS_I(inode)->reserved_extents);Simple test program below can reproduce this issue steadily. #include <string.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main(void) { int fd; char buf[1024*1024]; memset(buf, 0, 1024 * 1024); fd = open("testfile", O_CREAT | O_EXCL | O_RDWR); pwrite(fd, buf, 69954, 693581); return; } Assume the BTRFS_MAX_EXTENT_SIZE is 64KB, and data range is: 692224 765951 |----------------------------------------------------------------------------------| len(73728) 1) for the above data range, btrfs_delalloc_reserve_metadata() will reserve metadata and BTRFS_I(inode)->outstanding_extents will be 2. (73728 + 65535) / 65536 == 2 2) then btrfs_dirty_page() will be called to dirty pages and set EXTENT_DELALLOC flag. In this case, btrfs_set_bit_hook will be called 3 times. For first call, there will be such extent io map. 692224 696319 696320 765951 |----------------------| |-----------------------------------------------------| len(4096) len(69632) have EXTENT_DELALLOC and because of having EXTENT_FIRST_DELALLOC, btrfs_set_bit_hook() won't change BTRFS_I(inode)->outstanding_extents, still be 2. see code logic in btrfs_set_bit_hook(); 3) second btrfs_set_bit_hook() call. Because of EXTENT_FIRST_DELALLOC have been unset by previous btrfs_set_bit_hook(), btrfs_set_bit_hook will increase BTRFS_I(inode)->outstanding_extents by one, so now BTRFS_I(inode)->outstanding_extents, sitll is 3. There will be such extent_io map: 692224 696319 696320 761855 761856 765951 |--------------------| |---------------------| |--------------------------| len(4096) len(65536) len(4096) have EXTENT_DELALLOC have EXTENT_DELALLOC And because (692224, 696319) and (696320, 761855) is adjacent, btrfs_merge_extent_hook() will merge them into one delalloc extent, but according to the compulation logic in btrfs_merge_extent_hook(), BTRFS_I(inode)->outstanding_extents will still be 3. After merge, tehre will bu such extent_io map: 692224 761855 761856 765951 |-------------------------------------------------| |--------------------------| len(69632) len(4096) have EXTENT_DELALLOC 4) third btrfs_set_bit_hook() call. Also because of EXTENT_FIRST_DELALLOC have not been set, btrfs_set_bit_hook will increase BTRFS_I(inode)->outstanding_extents by one, so now BTRFS_I(inode)->outstanding_extents is 4. The extent io map is: 692224 761855 761856 765951 |-------------------------------------------------| |--------------------------| len(69632) len(4096) have EXTENT_DELALLOC have EXTENT_DELALLOC Also because (692224, 761855) and (761856, 765951) is adjacent, btrfs_merge_extent_hook() will merge them into one delalloc extent, according to the compulation logic in btrfs_merge_extent_hook(), BTRFS_I(inode)->outstanding_extents will decrease by one, be 3. so after merge, tehre will bu such extent_io map: 692224 765951 |-----------------------------------------------------------------------------------| len(73728) have EXTENT_DELALLOC But indeed for original data range(start:692224 end:765951 len:73728), we just should have 2 outstanding extents, so it will trigger the above WARNINGs. The root casue is that btrfs_delalloc_reserve_metadata() will always add needed outstanding extents first, and if later btrfs_set_extent_delalloc call multiple btrfs_set_bit_hook(), it may wrongly update BTRFS_I(inode)->outstanding_extents, This patch choose to also add BTRFS_I(inode)->outstanding_extents in btrfs_set_bit_hook() according to the data range length, and the added value is the correct number of outstanding_extents for this data range, then decrease the value which was added in btrfs_delalloc_reserve_metadata(). As for why BTRFS_MAX_EXTENT_SIZE(128M) does not trigger above WARNINGs, this is because __btrfs_buffered_write() internally have write limits for every iteration(it seems 2MB), so btrfs_dirty_pages() will always make data range into one outstanding extent. Signed-off-by: Wang Xiaoguang <wangxg.f...@cn.fujitsu.com>I haven't reviewed the code nor the the changelog, but from reading the test program and regardless of your fix, this should be trivial to test with xfs_io and make a test case for xfstests. So please write and submit a testcase for xfstests (taking into account the extent splitting happens at 128Mb of course).
Also don't you think the outstanding_extents computation in current btrfs code is not that nice. I think we should not do the "BTRFS_I(inode)->outstanding_extents++;" operation at all, we should always add number of extents according to the data rang length:
num_extents = div64_u64(len + BTRFS_MAX_EXTENT_SIZE - 1, + BTRFS_MAX_EXTENT_SIZE);
spin_lock(&BTRFS_I(inode)->lock);
BTRFS_I(inode)->outstanding_extents += num_extents;
spin_unlock(&BTRFS_I(inode)->lock);
Also let me explain more why I modify BTRFS_MAX_EXTENT_SIZE to 64KB to
have test.
When developing btrfs inband-dedupe feature, we often got ENOSPC error for metadata reservation, it's because when a file goes through in-band dedupe,its max extent size will be limited by in-band dedupe block size, so the compulation method based on 128MB in btrfs_delalloc_reserve_metadata() is not correct, obviously it should be based on in-band dedupe blocksize. So later I will also try to make
BTRFS_MAX_EXTENT_SIZE configurable. Regards, Xiaoguang Wang
Thanks.--- fs/btrfs/ctree.h | 2 ++ fs/btrfs/inode.c | 47 ++++++++++++++++++++++++++++++++++++++++++----- fs/btrfs/ioctl.c | 5 ++--- 3 files changed, 46 insertions(+), 8 deletions(-) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 84a6a5b..da9ee24 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -4072,6 +4072,8 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, int delay_iput, int nr); int btrfs_set_extent_delalloc(struct inode *inode, u64 start, u64 end, struct extent_state **cached_state); +int btrfs_set_extent_defrag(struct inode *inode, u64 start, u64 end, + struct extent_state **cached_state); int btrfs_create_subvol_root(struct btrfs_trans_handle *trans, struct btrfs_root *new_root, struct btrfs_root *parent_root, diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 41a5688..5144f45 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1713,13 +1713,16 @@ static void btrfs_set_bit_hook(struct inode *inode, if (!(state->state & EXTENT_DELALLOC) && (*bits & EXTENT_DELALLOC)) { struct btrfs_root *root = BTRFS_I(inode)->root; u64 len = state->end + 1 - state->start; + u64 num_extents = div64_u64(len + BTRFS_MAX_EXTENT_SIZE - 1, + BTRFS_MAX_EXTENT_SIZE); bool do_list = !btrfs_is_free_space_inode(inode); - if (*bits & EXTENT_FIRST_DELALLOC) { + if (*bits & EXTENT_FIRST_DELALLOC) *bits &= ~EXTENT_FIRST_DELALLOC; - } else { + + if (root != root->fs_info->tree_root) { spin_lock(&BTRFS_I(inode)->lock); - BTRFS_I(inode)->outstanding_extents++; + BTRFS_I(inode)->outstanding_extents += num_extents; spin_unlock(&BTRFS_I(inode)->lock); } @@ -1960,9 +1963,43 @@ static noinline int add_pending_csums(struct btrfs_trans_handle *trans, int btrfs_set_extent_delalloc(struct inode *inode, u64 start, u64 end, struct extent_state **cached_state) { + int ret; + struct btrfs_root *root = BTRFS_I(inode)->root; + u64 num_extents = div64_u64(end - start + BTRFS_MAX_EXTENT_SIZE, + BTRFS_MAX_EXTENT_SIZE); + + WARN_ON((end & (PAGE_CACHE_SIZE - 1)) == 0); + ret = set_extent_delalloc(&BTRFS_I(inode)->io_tree, start, end, + cached_state, GFP_NOFS); + + if (root != root->fs_info->tree_root) { + spin_lock(&BTRFS_I(inode)->lock); + BTRFS_I(inode)->outstanding_extents -= num_extents; + spin_unlock(&BTRFS_I(inode)->lock); + } + + return ret; +} + +int btrfs_set_extent_defrag(struct inode *inode, u64 start, u64 end, + struct extent_state **cached_state) +{ + int ret; + struct btrfs_root *root = BTRFS_I(inode)->root; + u64 num_extents = div64_u64(end - start + BTRFS_MAX_EXTENT_SIZE, + BTRFS_MAX_EXTENT_SIZE); + WARN_ON((end & (PAGE_CACHE_SIZE - 1)) == 0); - return set_extent_delalloc(&BTRFS_I(inode)->io_tree, start, end, - cached_state, GFP_NOFS); + ret = set_extent_defrag(&BTRFS_I(inode)->io_tree, start, end, + cached_state, GFP_NOFS); + + if (root != root->fs_info->tree_root) { + spin_lock(&BTRFS_I(inode)->lock); + BTRFS_I(inode)->outstanding_extents -= num_extents; + spin_unlock(&BTRFS_I(inode)->lock); + } + + return ret; } /* see btrfs_writepage_start_hook for details on why this is required */ diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 21423dd..149d11e 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1227,9 +1227,8 @@ again: } - set_extent_defrag(&BTRFS_I(inode)->io_tree, page_start, page_end - 1, - &cached_state, GFP_NOFS); - + btrfs_set_extent_defrag(inode, page_start, + page_end - 1, &cached_state); unlock_extent_cached(&BTRFS_I(inode)->io_tree, page_start, page_end - 1, &cached_state, GFP_NOFS); -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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