Re: [PATCH v2 10/12] btrfs: make balance_dirty_pages nowait compatible

[Stefan Roesch <shr@fb.com>]

On 9/8/22 3:16 AM, Filipe Manana wrote:
> > 
> On Thu, Sep 8, 2022 at 1:26 AM Stefan Roesch <shr@fb.com> wrote:
>>
>> This replaces the call to function balance_dirty_pages_ratelimited() in
>> the function btrfs_buffered_write() with a call to
>> balance_dirty_pages_ratelimited_flags().
>>
>> It also moves the function after the again label. This can cause the
>> function to be called a bit later, but this should have no impact in the
>> real world.
>>
>> Signed-off-by: Stefan Roesch <shr@fb.com>
>> ---
>>  fs/btrfs/file.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index 6e191e353b22..fd42ba9de7a7 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -1654,6 +1654,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>>         loff_t old_isize = i_size_read(inode);
>>         unsigned int ilock_flags = 0;
>>         bool nowait = iocb->ki_flags & IOCB_NOWAIT;
>> +       unsigned int bdp_flags = nowait ? BDP_ASYNC : 0;
>>
>>         if (nowait)
>>                 ilock_flags |= BTRFS_ILOCK_TRY;
>> @@ -1756,6 +1757,10 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>>
>>                 release_bytes = reserve_bytes;
>>  again:
>> +               ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags);
>> +               if (unlikely(ret))
> 
> We normally only use likely or unlikely in contextes where we observe
> that it makes a significant difference.
> What's the motivation here, have you verified that in this case it has
> a significant impact?
> 

I removed it.

> Thanks.
> 
>> +                       break;
>> +
>>                 /*
>>                  * This is going to setup the pages array with the number of
>>                  * pages we want, so we don't really need to worry about the
>> @@ -1860,8 +1865,6 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>>
>>                 cond_resched();
>>
>> -               balance_dirty_pages_ratelimited(inode->i_mapping);
>> -
>>                 pos += copied;
>>                 num_written += copied;
>>         }
>> --
>> 2.30.2
>>