Messages in this thread | | | Date | Fri, 14 Sep 2012 15:19:52 +0200 | From | Jan Kara <> | Subject | Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty() |
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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
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