Re: [PATCH] fs: Make sync_file_range(2) use WB_SYNC_NONE writeback

[Andres Freund <andres@anarazel.de>]

Hi Jan,

Thanks for looking into this and promptly sending a patch.

On 2015-10-24 21:28:17 +0200, Jan Kara wrote:
> These days do_sync_mapping_range() went away and we can switch
> sync_file_range(2) back to issuing WB_SYNC_NONE writeback. That should
> help PostgreSQL avoid large latency spikes when flushing data in the
> background.
> 
> diff --git a/fs/sync.c b/fs/sync.c
> index fbc98ee62044..ef60e812d771 100644
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@ -343,7 +343,8 @@ SYSCALL_DEFINE4(sync_file_range, int, fd, loff_t, offset, loff_t, nbytes,
>  	}
>  
>  	if (flags & SYNC_FILE_RANGE_WRITE) {
> -		ret = filemap_fdatawrite_range(mapping, offset, endbyte);
> +		ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
> +						 WB_SYNC_NONE);
>  		if (ret < 0)
>  			goto out_put;
>  	}

Thanks. Would scheduling a comparative benchmark of this be helpful
pushing htis forward ? Would probably only be early next week, I'm at
the european postgresql conference right now.

Regards,

Andres