On Fri, 2006-09-01 at 10:16 -0700, Dave Hansen wrote: > This feels like something that can be done with RCU. The > __page_discard() is the write operation, right? So, take an rcu write > lock inside of the page discard function, and read locks over the > current places where PG_discarded is set. > > That should make sure that the discard operation itself can't be done > concurrently with one of the __remove_from*() operations. Once the > write lock has been acquired, you just check page->mapping to see if the > a __remove_from*() operation has occurred while you waited. The problem of page discard vs. normal page remove is that the page can be remove and discarded at the same time. Both sides are writers in the sense that they want to remove the page from page cache. RCU doesn't not help with that kind of race. -- blue skies, Martin. Martin Schwidefsky Linux for zSeries Development & Services IBM Deutschland Entwicklung GmbH "Reality continues to ruin my life." - Calvin.
