kernel/linux.git/fs/btrfs/sysfs.c, branch v6.12.80

btrfs: introduce btrfs_space_info sub-group

2026-01-23T10:18:38+00:00

[ Upstream commit f92ee31e031c7819126d2febdda0c3e91f5d2eb9 ] Current code assumes we have only one space_info for each block group type (DATA, METADATA, and SYSTEM). We sometime need multiple space infos to manage special block groups. One example is handling the data relocation block group for the zoned mode. That block group is dedicated for writing relocated data and we cannot allocate any regular extent from that block group, which is implemented in the zoned extent allocator. This block group still belongs to the normal data space_info. So, when all the normal data block groups are full and there is some free space in the dedicated block group, the space_info looks to have some free space, while it cannot allocate normal extent anymore. That results in a strange ENOSPC error. We need to have a space_info for the relocation data block group to represent the situation properly. Adds a basic infrastructure for having a "sub-group" of a space_info: creation and removing. A sub-group space_info belongs to one of the primary space_infos and has the same flags as its parent. This commit first introduces the relocation data sub-space_info, and the next commit will introduce tree-log sub-space_info. In the future, it could be useful to implement tiered storage for btrfs e.g. by implementing a sub-group space_info for block groups resides on a fast storage. Reviewed-by: Johannes Thumshirn Signed-off-by: Naohiro Aota Signed-off-by: David Sterba Stable-dep-of: a11224a016d6 ("btrfs: fix memory leaks in create_space_info() error paths") Signed-off-by: Sasha Levin

btrfs: sysfs: fix direct super block member reads

2025-01-02T09:34:24+00:00

commit fca432e73db2bec0fdbfbf6d98d3ebcd5388a977 upstream. The following sysfs entries are reading super block member directly, which can have a different endian and cause wrong values: - sys/fs/btrfs//nodesize - sys/fs/btrfs//sectorsize - sys/fs/btrfs//clone_alignment Thankfully those values (nodesize and sectorsize) are always aligned inside the btrfs_super_block, so it won't trigger unaligned read errors, just endian problems. Fix them by using the native cached members instead. Fixes: df93589a1737 ("btrfs: export more from FS_INFO to sysfs") CC: stable@vger.kernel.org Reviewed-by: Naohiro Aota Reviewed-by: Johannes Thumshirn Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman

btrfs: introduce new "rescue=ignoresuperflags" mount option

2024-07-11T13:33:30+00:00

This new mount option allows the kernel to skip the super flags check, it's mostly to allow the kernel to do a rescue mount of an interrupted checksum conversion. Reviewed-by: Josef Bacik Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: introduce new "rescue=ignoremetacsums" mount option

2024-07-11T13:33:29+00:00

Introduce "rescue=ignoremetacsums" to ignore metadata csums, all the other metadata sanity checks are still kept as is. This new mount option is mostly to allow the kernel to mount an interrupted checksum conversion (at the metadata csum overwrite stage). And since the main part of metadata sanity checks is inside tree-checker, we shouldn't lose much safety, and the new mount option is rescue mount option it requires full read-only mount. Reviewed-by: Josef Bacik Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: periodic block_group reclaim

2024-07-11T13:33:27+00:00

We currently employ a edge-triggered block group reclaim strategy which marks block groups for reclaim as they free down past a threshold. With a dynamic threshold, this is worse than doing it in a level-triggered fashion periodically. That is because the reclaim itself happens periodically, so the threshold at that point in time is what really matters, not the threshold at freeing time. If we mark the reclaim in a big pass, then sort by usage and do reclaim, we also benefit from a negative feedback loop preventing unnecessary reclaims as we crunch through the "best" candidates. Since this is quite a different model, it requires some additional support. The edge triggered reclaim has a good heuristic for not reclaiming fresh block groups, so we need to replace that with a typical GC sweep mark which skips block groups that have seen an allocation since the last sweep. Reviewed-by: Josef Bacik Signed-off-by: Boris Burkov Signed-off-by: David Sterba

btrfs: dynamic block_group reclaim threshold

2024-07-11T13:33:27+00:00

We can currently recover allocated block_groups by: - explicitly starting balance operations - "auto reclaim" via bg_reclaim_threshold The latter works by checking against a fixed threshold on frees. If we pass from above the threshold to below, relocation triggers and the block group will get reclaimed by the cleaner thread (assuming it is still eligible) Picking a threshold is challenging. Too high, and you end up trying to reclaim very full block_groups which is quite costly, and you don't do reclaim on block_groups that don't get quite THAT full, but could still be quite fragmented and stranding a lot of space. Too low, and you similarly miss out on reclaim even if you badly need it to avoid running out of unallocated space, if you have heavily fragmented block groups living above the threshold. No matter the threshold, it suffers from a workload that happens to bounce around that threshold, which can introduce arbitrary amounts of reclaim waste. To improve this situation, introduce a dynamic threshold. The basic idea behind this threshold is that it should be very lax when there is plenty of unallocated space, and increasingly aggressive as we approach zero unallocated space. To that end, it sets a target for unallocated space (10 chunks) and then linearly increases the threshold as the amount of space short of the target we are increases. The formula is: (target - unalloc) / target I tested this by running it on three interesting workloads: 1. bounce allocations around X% full. 2. fill up all the way and introduce full fragmentation. 3. write in a fragmented way until the filesystem is just about full. 1. and 2. attack the weaknesses of a fixed threshold; fixed either works perfectly or fully falls apart, depending on the threshold. Dynamic always handles these cases well. 3. attacks dynamic by checking whether it is too zealous to reclaim in conditions with low unallocated and low unused. It tends to claw back 1GiB of unallocated fairly aggressively, but not much more. Early versions of dynamic threshold struggled on this test. Additional work could be done to intelligently ratchet up the urgency of reclaim in very low unallocated conditions. Existing mechanisms are already useless in that case anyway. Reviewed-by: Josef Bacik Signed-off-by: Boris Burkov Signed-off-by: David Sterba

btrfs: report reclaim stats in sysfs

2024-07-11T13:33:27+00:00

When evaluating various reclaim strategies/thresholds against each other, it is useful to collect data about the amount of reclaim happening. Expose a count, error count, and byte count via sysfs per space_info. Note that this is only for automatic reclaim, not manually invoked balances or other codepaths that use "relocate_block_group" Reviewed-by: Josef Bacik Reviewed-by: Johannes Thumshirn Signed-off-by: Boris Burkov Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: use btrfs_is_testing() everywhere

2024-05-07T19:31:07+00:00

There are open coded tests of BTRFS_FS_STATE_DUMMY_FS_INFO and we have a wrapper for that that's a compile-time constant when self-tests are not built in. As this is only for development we can save some bytes and conditions on release configs by using the helper in the remaining cases. Reviewed-by: Josef Bacik Signed-off-by: David Sterba

btrfs: introduce offload_csum_mode to tweak checksum offloading behavior

2024-03-04T15:24:52+00:00

We disable offloading checksum to workqueues and do it synchronously when the checksum algorithm is fast. However, as reported in the link below, RAID0 with multiple devices may suffer from the sync checksum, because "fast checksum" is still not fast enough to catch up with RAID0 writing. We don't have an effective way to determine whether to offload or not, for now add a sysfs knob so this can be debugged. This is intentionally under CONFIG_BTRFS_DEBUG so ti's not exposed to users as it may be removed in the future agin. Introduce fs_devices->offload_csum_mode, so that a btrfs developer can change the behavior by writing to /sys/fs/btrfs//offload_csum. The default is "auto" which is the same as the previous behavior. Or, you can set "on" or "off" (or "y" or "n" whatever kstrtobool() accepts) to always/never offload checksum. More benchmark need to be collected with this knob to implement a proper criteria to enable/disable checksum offloading. Link: https://lore.kernel.org/linux-btrfs/20230731152223.4EFB.409509F4@e16-tech.com/ Link: https://lore.kernel.org/linux-btrfs/p3vo3g7pqn664mhmdhlotu5dzcna6vjtcoc2hb2lsgo2fwct7k@xzaxclba5tae/ Reviewed-by: Johannes Thumshirn Signed-off-by: Naohiro Aota Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: sysfs: drop unnecessary double logical negation in acl_show()

2024-03-04T15:24:52+00:00

The IS_ENABLED() macro already guarantees the result will be a suitable boolean return value ("1" for enabled, and "0" for disabled). Thus, it seems that the "!!" used right before is unnecessary to force the 0/1 values. Reviewed-by: Anand Jain Signed-off-by: Neal Gompa Reviewed-by: David Sterba Signed-off-by: David Sterba