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

[Jan Kara <jack@suse.cz>]

  Hi Andres,

On Wed 28-10-15 10:30:40, Andres Freund wrote:
> 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.

If you could run it, it would be nice. Thanks!

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR