Messages in this thread | | | Date | Thu, 10 Sep 2009 08:57:42 -0400 | From | Chris Mason <> | Subject | Re: [RFC][PATCH 7/7] writeback: balance_dirty_pages() shall write more than dirtied pages |
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On Thu, Sep 10, 2009 at 09:42:01AM +0800, Wu Fengguang wrote: > On Wed, Sep 09, 2009 at 11:44:13PM +0800, Jan Kara wrote: > > On Wed 09-09-09 22:51:48, Wu Fengguang wrote: > > > Some filesystem may choose to write much more than ratelimit_pages > > > before calling balance_dirty_pages_ratelimited_nr(). So it is safer to > > > determine number to write based on real number of dirtied pages. > > > > > > The increased write_chunk may make the dirtier more bumpy. This is > > > filesystem writers' duty not to dirty too much at a time without > > > checking the ratelimit. > > I don't get this. balance_dirty_pages_ratelimited_nr() is called when we > > dirty the page, not when we write it out. So a problem would only happen if > > filesystem dirties pages by set_page_dirty() and won't call > > balance_dirty_pages_ratelimited_nr(). But e.g. generic_perform_write() > > and do_wp_page() takes care of that. So where's the problem? > > It seems that btrfs_file_write() is writing in chunks of up to 1024-pages > (1024 is the computed nrptrs value in a 32bit kernel). And it calls > balance_dirty_pages_ratelimited_nr() each time it dirtied such a chunk.
I can easily change this to call more often, but we do always call balance_dirty_pages to reflect how much ram we've really sent down.
-chris
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