> Eventually you'll have to swap frontswap pages, or kill uncooperative > guests. At which point all of the simplicity is gone. OK, now I think I see the crux of the disagreement. NO! Frontswap on Xen+tmem never *never* _never_ NEVER results in host swapping. Host swapping is evil. Host swapping is the root of most of the bad reputation that memory overcommit has gotten from VMware customers. Host swapping can't be avoided with some memory overcommit technologies (such as page sharing), but frontswap on Xen+tmem CAN and DOES avoid it. So, to summarize: 1) You agreed that a synchronous interface for frontswap makes sense for swap-to-in-kernel-compressed-RAM because it is truly swapping to RAM. 2) You have pointed out that an asynchronous interface for frontswap makes more sense for KVM than a synchronous interface, because KVM does host swapping. Then you said if you have an asynchronous interface anyway, the existing swap code works just fine with no changes so frontswap is not needed at all... for KVM. 3) You have suggested that if Xen were more like KVM and required host-swapping, then Xen doesn't need frontswap either. BUT frontswap on Xen+tmem always truly swaps to RAM. So there are two users of frontswap for which the synchronous interface makes sense. I believe there may be more in the future and you disagree but, as Jeremy said, "a general Linux principle is not to overdesign interfaces for hypothetical users, only for real needs." We have demonstrated there is a need with at least two users so the debate is only whether the number of users is two or more than two. Frontswap is a very non-invasive patch and is very cleanly layered so that if it is not in the presence of either of the intended "users", it can be turned off in many different ways with zero overhead (CONFIG'ed off) or extremely small overhead (frontswap_ops is never set; or frontswap_ops is set but the underlying hypervisor doesn't support it so frontswap_poolid never gets set). So... KVM doesn't need it and won't use it. Do you, Avi, have any other objections as to why the frontswap patch shouldn't be accepted as is for the users that DO need it and WILL use it? -- 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