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SubjectRe: [PATCH 03/17] writeback: introduce writeback_control.inodes_cleaned
On Mon, May 16, 2011 at 06:40:16PM +0800, Christoph Hellwig wrote:
> On Mon, May 16, 2011 at 09:50:21AM +1000, Dave Chinner wrote:
> > > - nr_to_write has always been "# of pages written" and writeback_sb_inodes()
> > > is actually making use of it to do page accounting in work->nr_pages.
> >
> > Do we really care whether it's inodes or pages that are written? As
> > far as i can tell it doesn't, because writing inodes generally
> > requires more IO and so needs to be limited anyway.
>
> We do care, but the current infrastructure already is bad enough to
> not make it work. E.g. when calling from balance_dirty_pages we
> couldn't care less if the inode is written back, we just want pages
> on stable storage, similar for wakeups from the VM code. Sooner or
> later there's no way around splitting page and inode writeback
> completely.

Agreed.

> > So put the accounting in the post-write code in
> > writeback_single_inode() where we already check if the inode is
> > still dirty or not. Splitting per-inode post-write processing
> > between writeback_single_inode and the higher level code is cludgy -
> > I'd much prefer it done in only one place.
>
> I'd tend to agree. Especially as cleaner separation was the main
> goal for getting rid of the writeback_control overload in the beginning.

I wonder if this is what you want, which puts page and inode
accounting together:

writeback_single_inode(inode, wb, &wbc);

work->nr_pages -= write_chunk - wbc.nr_to_write;
wrote += write_chunk - wbc.nr_to_write;
+ if (!(inode->i_state & I_DIRTY))
+ wrote++;
+
if (wbc.pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode, wb);
}

Thanks,
Fengguang


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