On Fri, 30 Apr 2010 09:08:00 -0700 Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, 2010-04-30 at 08:59 -0700, Dan Magenheimer wrote: > > Dave or others can correct me if I am wrong, but I think CMM2 also > > handles dirty pages that must be retained by the hypervisor. The > > difference between CMM2 (for dirty pages) and frontswap is that > > CMM2 sets hints that can be handled asynchronously while frontswap > > provides explicit hooks that synchronously succeed/fail. > > Once pages were dirtied (or I guess just slightly before), they became > volatile, and I don't think the hypervisor could do anything with them. > It could still swap them out like usual, but none of the CMM-specific > optimizations could be performed. Well, almost correct :-) A dirty page (or one that is about to become dirty) can be in one of two CMMA states: 1) stable This is the case for pages where the kernel is doing some operation on the page that will make it dirty, e.g. I/O. Before the kernel can allow the operation the page has to be made stable. If the state conversion to stable fails because the hypervisor removed the page the page needs to get deleted from page cache and recreated from scratch. 2) potentially-volatile This state is used for page cache pages for which a writable mapping exists. The page can be removed by the hypervisor as long as the physical per-page dirty bit is not set. As soon as the bit is set the page is considered stable although the CMMA state still is potentially- volatile. In both cases the only thing the hypervisor can do with a dirty page is to swap it as usual. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>