On 2018/8/29 下午9:43, Nikolay Borisov wrote:
>
>
> On 29.08.2018 08:15, Qu Wenruo wrote:
>> Function btrfs_trim_fs() doesn't handle errors in a consistent way, if
>> error happens when trimming existing block groups, it will skip the
>> remaining blocks and continue to trim unallocated space for each device.
>>
>> And the return value will only reflect the final error from device
>> trimming.
>>
>> This patch will fix such behavior by:
>>
>> 1) Recording last error from block group or device trimming
>> So return value will also reflect the last error during trimming.
>> Make developer more aware of the problem.
>>
>> 2) Continuing trimming if we can
>> If we failed to trim one block group or device, we could still try
>> next block group or device.
>>
>> 3) Report number of failures during block group and device trimming
>> So it would be less noisy, but still gives user a brief summary of
>> what's going wrong.
>>
>> Such behavior can avoid confusion for case like failure to trim the
>> first block group and then only unallocated space is trimmed.
>>
>> Reported-by: Chris Murphy <li...@colorremedies.com>
>> Signed-off-by: Qu Wenruo <w...@suse.com>
>> ---
>> fs/btrfs/extent-tree.c | 57 ++++++++++++++++++++++++++++++------------
>> 1 file changed, 41 insertions(+), 16 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index de6f75f5547b..7768f206196a 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -10832,6 +10832,16 @@ static int btrfs_trim_free_extents(struct
>> btrfs_device *device,
>> return ret;
>> }
>>
>> +/*
>> + * Trim the whole fs, by:
>> + * 1) Trimming free space in each block group
>> + * 2) Trimming unallocated space in each device
>> + *
>> + * Will try to continue trimming even if we failed to trim one block group
>> or
>> + * device.
>> + * The return value will be the last error during trim.
>> + * Or 0 if nothing wrong happened.
>> + */
>> int btrfs_trim_fs(struct btrfs_fs_info *fs_info, struct fstrim_range *range)
>> {
>> struct btrfs_block_group_cache *cache = NULL;
>> @@ -10842,6 +10852,10 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info,
>> struct fstrim_range *range)
>> u64 end;
>> u64 trimmed = 0;
>> u64 total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
>> + u64 bg_failed = 0;
>> + u64 dev_failed = 0;
>> + int bg_ret = 0;
>> + int dev_ret = 0;
>> int ret = 0;
>>
>> /*
>> @@ -10852,7 +10866,7 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info,
>> struct fstrim_range *range)
>> else
>> cache = btrfs_lookup_block_group(fs_info, range->start);
>>
>> - while (cache) {
>> + for (; cache; cache = next_block_group(fs_info, cache)) {
>> if (cache->key.objectid >= (range->start + range->len)) {
>> btrfs_put_block_group(cache);
>> break;
>> @@ -10866,45 +10880,56 @@ int btrfs_trim_fs(struct btrfs_fs_info *fs_info,
>> struct fstrim_range *range)
>> if (!block_group_cache_done(cache)) {
>> ret = cache_block_group(cache, 0);
>> if (ret) {
>> - btrfs_put_block_group(cache);
>> - break;
>> + bg_failed++;
>> + bg_ret = ret;
>> + continue;
>> }
>> ret = wait_block_group_cache_done(cache);
>> if (ret) {
>> - btrfs_put_block_group(cache);
>> - break;
>> + bg_failed++;
>> + bg_ret = ret;
>> + continue;
>> }
>> }
>> - ret = btrfs_trim_block_group(cache,
>> - &group_trimmed,
>> - start,
>> - end,
>> - range->minlen);
>> + ret = btrfs_trim_block_group(cache, &group_trimmed,
>> + start, end, range->minlen);
>>
>> trimmed += group_trimmed;
>> if (ret) {
>> - btrfs_put_block_group(cache);
>> - break;
>> + bg_failed++;
>> + bg_ret = ret;
>> + continue;
>> }
>> }
>> -
>> - cache = next_block_group(fs_info, cache);
>> }
>>
>> + if (bg_failed)
>> + btrfs_warn(fs_info,
>> + "failed to trim %llu block group(s), last error was %d",
>> + bg_failed, bg_ret);
>
> IMO this error handling strategy doesn't really bring any value. The
> only thing which the user really gathers from that error message is that
> N block groups failed. But there is no information whether it failed due
> to read failure hence cannot load the freespace cache or there was some
> error during the actual trimming.
>
> I agree that if we fail for 1 bg we shouldn't terminate the whole
> process but just skip it. However, a more useful error handling strategy
> would be to have btrfs_warns for every failed block group for every
> failed function.
Yep, previous version goes that way.
But even for btrfs_warn_rl() it could be too noisy.
And just as commented by David, user may not even care, thus such too
noisy report makes not much sense.
E.g. if something really went wrong and make the fs RO, then there will
be tons of error messages flooding dmesg (although most of them will be
rate limited), and really makes no sense.
Thanks,
Qu
> I.e one for wait_block_group_cache since the low-level
> code in cache_block_group already prints something if it encounters
> errors. And one for btrfs_trim_block_group
>
>> mutex_lock(&fs_info->fs_devices->device_list_mutex);
>> devices = &fs_info->fs_devices->alloc_list;
>> list_for_each_entry(device, devices, dev_alloc_list) {
>> ret = btrfs_trim_free_extents(device, range->minlen,
>> &group_trimmed);
>> - if (ret)
>> + if (ret) {
>> + dev_failed++;
>> + dev_ret = ret;
>> break;
>> + }
>>
>> trimmed += group_trimmed;
>> }
>> mutex_unlock(&fs_info->fs_devices->device_list_mutex);
>>
>> + if (dev_failed)
>> + btrfs_warn(fs_info,
>> + "failed to trim %llu device(s), last error was %d",
>> + dev_failed, dev_ret);
>
> Same thing here, I'd rather see one message per device error and also
> identify the device by name.
>
>> range->len = trimmed;
>> - return ret;
>> + if (bg_ret)
>> + return bg_ret;
>> + return dev_ret;
>> }
>>
>> /*
>>
