On Wed, 2011-09-07 at 08:56 +0200, Christoph Hellwig wrote: > On Wed, Sep 07, 2011 at 02:22:22AM +0200, Jan Kara wrote: > > > So wtf is ext4 doing? Shouldn't a page stay dirty until its written out? > > > > > > That is, should we really frob around this behaviour or fix ext4 because > > > its on crack? > > Fengguang, could you please verify your findings with recent kernel? I > > believe ext4 got fixed in this regard some time ago already (and yes, old > > delalloc writeback code in ext4 was terrible). > > The pattern we do in writeback is: > > in pageout / write_cache_pages: > lock_page(); > clear_page_dirty_for_io(); > > in ->writepage: > set_page_writeback(); > unlock_page(); > end_page_writeback(); > > So whenever ->writepage decides it doesn't want to write things back > we have to redirty pages. We have this happen quite a bit in every > filesystem, but ext4 hits it a lot more than usual because it refuses > to write out delalloc pages from plain ->writepage and only allows > ->writepages to do it. Ah, right, so it is a fairly common thing and not something easily fixed in filesystems. Ok so I guess the patch is good. Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
