Re: [PATCH v3 2/4] ovl: use vfs_clone_file_range() for copy up if possible

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Sep 21, 2016 at 6:09 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Wed, Sep 14, 2016 at 2:43 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>> When copying up within the same fs, try to use vfs_clone_file_range().
>> This is very efficient when lower and upper are on the same fs
>> with file reflink support. If vfs_clone_file_range() fails because
>> lower and upper are not on the same fs or if fs has no reflink support,
>> copy up falls back to the regular data copy code.
>>
>> Tested correct behavior when lower and upper are on:
>> 1. same ext4 (copy)
>> 2. same xfs + reflink patches + mkfs.xfs (copy)
>> 3. same xfs + reflink patches + mkfs.xfs -m reflink=1 (reflink)
>> 4. different xfs + reflink patches + mkfs.xfs -m reflink=1 (copy)
>>
>> For comparison, on my laptop, xfstest overlay/001 (copy up of large
>> sparse files) takes less than 1 second in the xfs reflink setup vs.
>> 25 seconds on the rest of the setups.
>>
>> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>> ---
>>  fs/overlayfs/copy_up.c | 12 +++++++++++-
>>  1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
>> index 43fdc27..ba039f8 100644
>> --- a/fs/overlayfs/copy_up.c
>> +++ b/fs/overlayfs/copy_up.c
>> @@ -136,6 +136,16 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
>>                 goto out_fput;
>>         }
>>
>> +       /* Try to use clone_file_range to clone up within the same fs */
>> +       error = vfs_clone_file_range(old_file, 0, new_file, 0, len);
>> +       if (!error)
>> +               goto out;
>> +       /* If we can clone but clone failed - abort */
>> +       if (error != -EXDEV && error != -EOPNOTSUPP)
>> +               goto out;
>
> Would be safer to fall back on any error.
>

Agreed. Dave, since you suggested the 'softer' fall back, do you have
any objections?

> Otherwise ACK.
>

Will you be taking this to your tree?

Please note that this patch depends on patch v3 1/4,
because vfs_clone_file_range() in current mainline
fails to clone from lower to upper due to upper and lower being
private mount clones
and therefore not the same f_path.mnt.

Thanks,
Amir.