On Wed, 18 Jun 2008 16:42:37 +1000 Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote: > > (This fix is not related to lock_page() problem.) > > > > If I read your advice correctly, we shouldn't use lock_page() here. > > > > Before speculative page cache, page_table_entry of a page under migration > > has a pte entry which encodes pfn as special pte entry. and wait for the > > end of page migration by lock_page(). > > What I don't think I understand, is how we can have a page in the > page tables (and with the ptl held) but with a zero refcount... Oh, > it's not actually a page but a migration entry! I'm not quite so > familiar with that code. > > Hmm, so we might possibly see a page there that has a zero refcount > due to page_freeze_refs? In which case, I think the direction of you > fix is good. Sorry for my misunderstanding the problem, and thank > you for fixing up my code! > > I would ask you to use get_page_unless_zero rather than > page_cache_get_speculative(), because it's not exactly a speculative > reference -- a speculative reference is one where we elevate _count > and then must recheck that the page we have is correct. > ok. > Also, please add a comment. It would really be nicer to hide this > transiently-frozen state away from migration_entry_wait, but I can't > see any lock that would easily solve it. > ok, will adds comments. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
