Write drop behind logic with used-once patch

[Marcelo Tosatti]

Hi Daniel,

As far as I can see, the write drop behind logic with the used-once patch
is partly "gone" now: "check_used_once()" at generic_file_write() will set
all "write()n" pages to have age == PAGE_AGE_START (in case those pages
were not in cache before), which means they will be moved to the active
list later by page_launder(), effectively causing excessive pressure on
the current "active" pages since we have exponential page aging.

I'm I overlooking some here or my thinking is correct ?