On Wed, Sep 07, 2011 at 06:42:16PM +0200, Jan Kara wrote:

  Well, it depends on what you call common - usually, ->writepage is called
from kswapd which shouldn't be common compared to writeback from a flusher
thread. But now I've realized that JBD2 also calls ->writepage to fulfill
data=ordered mode guarantees and that's what causes most of redirtying of
pages on ext4. That's going away eventually but it will take some time. So
for now writeback has to handle redirtying...

Under the "right" loads it may also happen for xfs because we can't
take lock non-blockingly in the fluser thread for example.

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