On 12.12.2017 09:34, Qu Wenruo wrote: > [Overall] > The previous rework on qgroup reservation system put a lot of effort on > data, which works quite fine. > > But it takes less focus on metadata reservation, causing some problem > like metadata reservation underflow and noisy kernel warning. > > This patchset will try to address the remaining problem of metadata > reservation. > > The idea of new qgroup metadata reservation is to use 2 types of > metadata reservation: > 1) Per-transaction reservation > Life span will be inside a transaction. Will be freed at transaction > commit time. > > 2) Preallocated reservation > For case where we reserve space before starting a transaction. > Operation like dealloc and delayed-inode/item belongs to this type. > > This works similar to block_rsv, its reservation can be > reserved/released at any timing caller like. > > The only point to notice is, if preallocated reservation is used and > finished without problem, it should be converted to per-transaction > type instead of just freeing. > This is to co-operate with qgroup update at commit time. > > For preallocated type, this patch will integrate them into inode_rsv > mechanism reworked by Josef, and delayed-inode/item reservation. > > > [Problem: Over-reserve] > Currently the patchset addresses metadata underflow quite well, but > due to the over-reserve nature of btrfs and highly bounded to inode_rsv, > qgroup metadata reservation also tends to be over-reserved. > > This is especially obvious for small limit. > For 128M limit, it's will only be able to write about 70M before hitting > quota limit. > Although for larger limit, like 5G limit, it can reach 4.5G or more > before hitting limit. > > Such over-reserved behavior can lead to some problem with existing test > cases (where limit is normally less than 20M). > > While it's also possible to be addressed by use more accurate space other > than max estimations. > > For example, to calculate metadata needed for delalloc, we use > btrfs_calc_trans_metadata_size(), which always try to reserve space for > CoW a full-height tree, and will also include csum size. > Both calculate is way over-killed for qgroup metadata reservation. In private chat with Chris couple of months ago we discussed making the reservation a lot less pessimistic. One assumption which we could exploit is the fact that upon a tree split it's unlikely we will create more than 1 additional level in the tree. So we could potentially modify btrfs_calc_trans_metadata_size to take a root parameter and instead of
BTRFS_MAX_LEVEL * 2 we could change this to root_level * 2. How does that sound? > > [Patch structure] > The patch is consist of 2 main parts: > 1) Type based qgroup reservation > The original patchset is sent several months ago. > Nothing is modified at all, just rebased. And not conflict at all. > > It's from patch 1 to patch 6. > > 2) Split meta qgroup reservation into per-trans and prealloc sub types > The real work to address metadata underflow. > Due to the over-reserve problem, this part is still in RFC state. > But the framework should mostly be fine, only needs extra fine-tuning > to get more accurate qgroup rsv to avoid too early limit. > > It's from patch 7 to 14. > > Qu Wenruo (14): > btrfs: qgroup: Skeleton to support separate qgroup reservation type > btrfs: qgroup: Introduce helpers to update and access new qgroup rsv > btrfs: qgroup: Make qgroup_reserve and its callers to use separate > reservation type > btrfs: qgroup: Fix wrong qgroup reservation update for relationship > modification > btrfs: qgroup: Update trace events to use new separate rsv types > btrfs: qgroup: Cleanup the remaining old reservation counters > btrfs: qgroup: Split meta rsv type into meta_prealloc and > meta_pertrans > btrfs: qgroup: Don't use root->qgroup_meta_rsv for qgroup > btrfs: qgroup: Introduce function to convert META_PREALLOC into > META_PERTRANS > btrfs: qgroup: Use separate meta reservation type for delalloc > btrfs: delayed-inode: Use new qgroup meta rsv for delayed inode and > item > btrfs: qgroup: Use root->qgroup_meta_rsv_* to record qgroup meta > reserved space > btrfs: qgroup: Update trace events for metadata reservation > Revert "btrfs: qgroups: Retry after commit on getting EDQUOT" > > fs/btrfs/ctree.h | 15 +- > fs/btrfs/delayed-inode.c | 50 +++++-- > fs/btrfs/disk-io.c | 2 +- > fs/btrfs/extent-tree.c | 49 +++--- > fs/btrfs/file.c | 15 +- > fs/btrfs/free-space-cache.c | 2 +- > fs/btrfs/inode-map.c | 4 +- > fs/btrfs/inode.c | 27 ++-- > fs/btrfs/ioctl.c | 10 +- > fs/btrfs/ordered-data.c | 2 +- > fs/btrfs/qgroup.c | 350 > ++++++++++++++++++++++++++++++++----------- > fs/btrfs/qgroup.h | 102 ++++++++++++- > fs/btrfs/relocation.c | 9 +- > fs/btrfs/transaction.c | 8 +- > include/trace/events/btrfs.h | 73 ++++++++- > 15 files changed, 537 insertions(+), 181 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
