lkml.org 
[lkml]   [2012]   [Sep]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty()
On Fri 14-09-12 21:12:02, OGAWA Hirofumi wrote:
> Fengguang Wu <fengguang.wu@intel.com> writes:
> >> >> @@ -120,6 +120,9 @@ __bdi_start_writeback(struct backing_dev
> >> >> {
> >> >> struct wb_writeback_work *work;
> >> >>
> >> >> + if (!bdi_cap_writeback_dirty(bdi))
> >> >> + return;
> >> >
> >> > Will someone in the current kernel actually call
> >> > __bdi_start_writeback() on a BDI_CAP_NO_WRITEBACK bdi?
> >> >
> >> > If the answer is no, VM_BUG_ON(!bdi_cap_writeback_dirty(bdi)) looks better.
> >>
> >> I guess nobody call it in current kernel though. Hmm.., but we also have
> >> check in __mark_inode_dirty(), nobody should be using it, right?
> >>
> >> If we defined it as the bug, I can't see what BDI_CAP_NO_WRITEBACK wants
> >> to do actually. We are not going to allow to disable the writeback task?
> >
> >> I was going to use this to disable writeback task on my developing FS...
> >
> > That sounds like an interesting use case. Can you elaborate a bit more?
> >
> > Note that even if you disable __bdi_start_writeback() here, the kernel
> > may also start writeback in the page reclaim path, the fsync() path,
> > and perhaps more.
>
> page reclaim and fsync path have FS handler. So, FS can control those.
>
> The modern FS have to control to flush carefully. Many FSes are already
> ignoring if wbc->sync_mode != WB_SYNC_ALL (e.g. ext3_write_inode,
> nilfs_writepages), and have own FS task to flush.
Out of curiosity, what exactly do you need to control in your filesystem
that makes flusher thread unusable for you? You still have a lot of
flexibility with ->write_inode() and ->writepages() callbacks...

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


\
 
 \ /
  Last update: 2012-09-14 16:01    [W:0.328 / U:0.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site