Re: [PATCH 2/2] Btrfs: qgroup: Introduce a may_use to account space_info->bytes_may_use.

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 12/09/2014 11:55 PM, Josef Bacik wrote:
> On 12/09/2014 06:27 AM, Dongsheng Yang wrote:
>> Currently, for pre_alloc or delay_alloc, the bytes will be accounted
>> in space_info by the three guys.
>> space_info->bytes_may_use --- space_info->reserved --- space_info->used.
>> But on the other hand, in qgroup, there are only two counters to 
>> account the
>> bytes, qgroup->reserved and qgroup->excl. And qg->reserved accounts
>> bytes in space_info->bytes_may_use and qg->excl accounts bytes in
>> space_info->used. So the bytes in space_info->reserved is not accounted
>> in qgroup. If so, there is a window we can exceed the quota limit when
>> bytes is in space_info->reserved.
>>
>> Example:
>>     # btrfs quota enable /mnt
>>     # btrfs qgroup limit -e 10M /mnt
>>     # for((i=0;i<20;i++));do fallocate -l 1M /mnt/data$i; done
>>     # sync
>>     # btrfs qgroup show -pcre /mnt
>> qgroupid rfer     excl     max_rfer max_excl parent  child
>> -------- ----     ----     -------- -------- ------  -----
>> 0/5      20987904 20987904 0        10485760 ---     ---
>>
>> qg->excl is 20987904 larger than max_excl 10485760.
>>
>> This patch introduce a new counter named may_use to qgroup, then
>> there are three counters in qgroup to account bytes in space_info
>> as below.
>> space_info->bytes_may_use --- space_info->reserved --- space_info->used.
>> qgroup->may_use           --- qgroup->reserved     --- qgroup->excl
>>
>> With this patch applied:
>>     # btrfs quota enable /mnt
>>     # btrfs qgroup limit -e 10M /mnt
>>     # for((i=0;i<20;i++));do fallocate -l 1M /mnt/data$i; done
>> fallocate: /mnt/data9: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data10: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data11: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data12: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data13: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data14: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data15: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data16: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data17: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data18: fallocate failed: Disk quota exceeded
>> fallocate: /mnt/data19: fallocate failed: Disk quota exceeded
>>     # sync
>>     # btrfs qgroup show -pcre /mnt
>> qgroupid rfer    excl    max_rfer max_excl parent  child
>> -------- ----    ----    -------- -------- ------  -----
>> 0/5      9453568 9453568 0        10485760 ---     ---
>>
>> Reported-by: Cyril SCETBON <cyril.scetbon@free.fr>
>> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
>> ---
>>   fs/btrfs/extent-tree.c | 25 ++++++++++++++++++-
>>   fs/btrfs/inode.c       | 22 +++++++++++++++-
>>   fs/btrfs/qgroup.c      | 68 
>> +++++++++++++++++++++++++++++++++++++++++++++++---
>>   fs/btrfs/qgroup.h      |  4 +++
>>   4 files changed, 113 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 014b7f2..9eaf268 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -5500,8 +5500,13 @@ static int pin_down_extent(struct btrfs_root 
>> *root,
>>
>>       set_extent_dirty(root->fs_info->pinned_extents, bytenr,
>>                bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
>> -    if (reserved)
>> +    if (reserved) {
>> +        if (root->fs_info->quota_enabled)
>
> You already have this check in btrfs_qgroup_update_reserved_bytes, 
> just call it unconditionally everywhere in this patch.  Otherwise this 
> looks good, thanks,

Thanx, I will update it in V2.
>
> Josef
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