Re: [PATCH v4 05/18] btrfs: delayed-ref: Add support for atomic increasing extent ref

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Qu Wenruo wrote on 2016/01/15 09:16 +0800:
> Hi Filipe,
>
> Thanks for your review.
>
> Filipe Manana wrote on 2016/01/14 09:56 +0000:
>> On Thu, Jan 14, 2016 at 5:57 AM, Qu Wenruo <quwenruo@cn.fujitsu.com>
>> wrote:
>>> Slightly modify btrfs_add_delayed_data_ref() to allow it accept
>>> GFP_ATOMIC, and allow it to do be called inside a spinlock.
>>
>> Hi Qu,
>>
>> I really would prefer to avoid gfp_atomic allocations.
>> Instead of using them, how about changing the approach so that callers
>> allocate the ref structure (without using gfp_atomic), then take the
>> spinlock, and then pass the structure to the inc/dec ref functions?
>
> Yes, we also considered that method too.
>
> But since it's only used for dedup hit case which has no existing
> delayed ref head, it's on a uncommon routine.
>
> On the other hand, if using the method you mentioned, alloc memory first
> then pass it to add_delayed_data_ref(), we will always need to alloc
> memory for minority cases.
>
> It would be very nice if you can provide some extra disadvantage on
> using GFP_ATOMIC, maybe there is something important I missed.
>
> Thanks
> Qu
>

My previous comment is totally wrong.

Such ATOMIC allocation failure has happened twice, much much more 
possible than I expected.

So I'll use the method mentioned.

Thanks,
Qu

>>
>> thanks
>>
>>>
>>> This is used by later dedup patches.
>>>
>>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>>> ---
>>>   fs/btrfs/ctree.h       |  4 ++++
>>>   fs/btrfs/delayed-ref.c | 25 +++++++++++++++++--------
>>>   fs/btrfs/delayed-ref.h |  2 +-
>>>   fs/btrfs/extent-tree.c | 24 +++++++++++++++++++++---
>>>   4 files changed, 43 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 2132fa5..671be87 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -3539,6 +3539,10 @@ int btrfs_inc_extent_ref(struct
>>> btrfs_trans_handle *trans,
>>>                           struct btrfs_root *root,
>>>                           u64 bytenr, u64 num_bytes, u64 parent,
>>>                           u64 root_objectid, u64 owner, u64 offset);
>>> +int btrfs_inc_extent_ref_atomic(struct btrfs_trans_handle *trans,
>>> +                               struct btrfs_root *root, u64 bytenr,
>>> +                               u64 num_bytes, u64 parent,
>>> +                               u64 root_objectid, u64 owner, u64
>>> offset);
>>>
>>>   int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans,
>>>                                     struct btrfs_root *root);
>>> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
>>> index 914ac13..e869442 100644
>>> --- a/fs/btrfs/delayed-ref.c
>>> +++ b/fs/btrfs/delayed-ref.c
>>> @@ -812,26 +812,31 @@ int btrfs_add_delayed_data_ref(struct
>>> btrfs_fs_info *fs_info,
>>>                                 u64 bytenr, u64 num_bytes,
>>>                                 u64 parent, u64 ref_root,
>>>                                 u64 owner, u64 offset, u64 reserved,
>>> int action,
>>> -                              struct btrfs_delayed_extent_op
>>> *extent_op)
>>> +                              int atomic)
>>>   {
>>>          struct btrfs_delayed_data_ref *ref;
>>>          struct btrfs_delayed_ref_head *head_ref;
>>>          struct btrfs_delayed_ref_root *delayed_refs;
>>>          struct btrfs_qgroup_extent_record *record = NULL;
>>> +       gfp_t gfp_flags;
>>> +
>>> +       if (atomic)
>>> +               gfp_flags = GFP_ATOMIC;
>>> +       else
>>> +               gfp_flags = GFP_NOFS;
>>>
>>> -       BUG_ON(extent_op && !extent_op->is_data);
>>> -       ref = kmem_cache_alloc(btrfs_delayed_data_ref_cachep, GFP_NOFS);
>>> +       ref = kmem_cache_alloc(btrfs_delayed_data_ref_cachep,
>>> gfp_flags);
>>>          if (!ref)
>>>                  return -ENOMEM;
>>>
>>> -       head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep,
>>> GFP_NOFS);
>>> +       head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep,
>>> gfp_flags);
>>>          if (!head_ref) {
>>>                  kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
>>>                  return -ENOMEM;
>>>          }
>>>
>>>          if (fs_info->quota_enabled && is_fstree(ref_root)) {
>>> -               record = kmalloc(sizeof(*record), GFP_NOFS);
>>> +               record = kmalloc(sizeof(*record), gfp_flags);
>>>                  if (!record) {
>>>
>>> kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
>>>                          kmem_cache_free(btrfs_delayed_ref_head_cachep,
>>> @@ -840,10 +845,13 @@ int btrfs_add_delayed_data_ref(struct
>>> btrfs_fs_info *fs_info,
>>>                  }
>>>          }
>>>
>>> -       head_ref->extent_op = extent_op;
>>> +       head_ref->extent_op = NULL;
>>>
>>>          delayed_refs = &trans->transaction->delayed_refs;
>>> -       spin_lock(&delayed_refs->lock);
>>> +
>>> +       /* For atomic case, caller should already hold the
>>> delayed_refs lock */
>>> +       if (!atomic)
>>> +               spin_lock(&delayed_refs->lock);
>>>
>>>          /*
>>>           * insert both the head node and the new ref without dropping
>>> @@ -856,7 +864,8 @@ int btrfs_add_delayed_data_ref(struct
>>> btrfs_fs_info *fs_info,
>>>          add_delayed_data_ref(fs_info, trans, head_ref, &ref->node,
>>> bytenr,
>>>                                     num_bytes, parent, ref_root,
>>> owner, offset,
>>>                                     action);
>>> -       spin_unlock(&delayed_refs->lock);
>>> +       if (!atomic)
>>> +               spin_unlock(&delayed_refs->lock);
>>>
>>>          return 0;
>>>   }
>>> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
>>> index c24b653..e34f96a 100644
>>> --- a/fs/btrfs/delayed-ref.h
>>> +++ b/fs/btrfs/delayed-ref.h
>>> @@ -249,7 +249,7 @@ int btrfs_add_delayed_data_ref(struct
>>> btrfs_fs_info *fs_info,
>>>                                 u64 bytenr, u64 num_bytes,
>>>                                 u64 parent, u64 ref_root,
>>>                                 u64 owner, u64 offset, u64 reserved,
>>> int action,
>>> -                              struct btrfs_delayed_extent_op
>>> *extent_op);
>>> +                              int atomic);
>>>   int btrfs_add_delayed_qgroup_reserve(struct btrfs_fs_info *fs_info,
>>>                                       struct btrfs_trans_handle *trans,
>>>                                       u64 ref_root, u64 bytenr, u64
>>> num_bytes);
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>> index 60cc139..4a01ca9 100644
>>> --- a/fs/btrfs/extent-tree.c
>>> +++ b/fs/btrfs/extent-tree.c
>>> @@ -2105,11 +2105,29 @@ int btrfs_inc_extent_ref(struct
>>> btrfs_trans_handle *trans,
>>>                  ret = btrfs_add_delayed_data_ref(fs_info, trans,
>>> bytenr,
>>>                                          num_bytes, parent,
>>> root_objectid,
>>>                                          owner, offset, 0,
>>> -                                       BTRFS_ADD_DELAYED_REF, NULL);
>>> +                                       BTRFS_ADD_DELAYED_REF, 0);
>>>          }
>>>          return ret;
>>>   }
>>>
>>> +int btrfs_inc_extent_ref_atomic(struct btrfs_trans_handle *trans,
>>> +                               struct btrfs_root *root, u64 bytenr,
>>> +                               u64 num_bytes, u64 parent,
>>> +                               u64 root_objectid, u64 owner, u64
>>> offset)
>>> +{
>>> +       struct btrfs_fs_info *fs_info = root->fs_info;
>>> +
>>> +       BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID &&
>>> +              root_objectid == BTRFS_TREE_LOG_OBJECTID);
>>> +
>>> +       /* Only used by dedup, so only data is possible */
>>> +       if (WARN_ON(owner < BTRFS_FIRST_FREE_OBJECTID))
>>> +               return -EINVAL;
>>> +       return btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
>>> +                       num_bytes, parent, root_objectid,
>>> +                       owner, offset, 0, BTRFS_ADD_DELAYED_REF, 1);
>>> +}
>>> +
>>>   static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
>>>                                    struct btrfs_root *root,
>>>                                    struct btrfs_delayed_ref_node *node,
>>> @@ -6893,7 +6911,7 @@ int btrfs_free_extent(struct btrfs_trans_handle
>>> *trans, struct btrfs_root *root,
>>>                                                  num_bytes,
>>>                                                  parent,
>>> root_objectid, owner,
>>>                                                  offset, 0,
>>> -
>>> BTRFS_DROP_DELAYED_REF, NULL);
>>> +
>>> BTRFS_DROP_DELAYED_REF, 0);
>>>          }
>>>          return ret;
>>>   }
>>> @@ -7845,7 +7863,7 @@ int btrfs_alloc_reserved_file_extent(struct
>>> btrfs_trans_handle *trans,
>>>                                           ins->offset, 0,
>>>                                           root_objectid, owner, offset,
>>>                                           ram_bytes,
>>> BTRFS_ADD_DELAYED_EXTENT,
>>> -                                        NULL);
>>> +                                        0);
>>>          return ret;
>>>   }
>>>
>>> --
>>> 2.7.0
>>>
>>>
>>>
>>> --
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>>
>>
>>