> From: Avi Kivity [mailto:avi@xxxxxxxxxx] > Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window) > > On 11/02/2011 06:02 PM, Andrea Arcangeli wrote: > > Hi Avi, > > > > On Wed, Nov 02, 2011 at 05:44:50PM +0200, Avi Kivity wrote: > > > If you look at cleancache, then it addresses this concern - it extends > > > pagecache through host memory. When dropping a page from the tail of > > > the LRU it first goes into tmem, and when reading in a page from disk > > > you first try to read it from tmem. However in many workloads, > > > cleancache is actually detrimental. If you have a lot of cache misses, > > > then every one of them causes a pointless vmexit; considering that > > > servers today can chew hundreds of megabytes per second, this adds up. > > > On the other side, if you have a use-once workload, then every page that > > > falls of the tail of the LRU causes a vmexit and a pointless page copy. > > > > I also think it's bad design for Virt usage, but hey, without this > > they can't even run with cache=writeback/writethrough and they're > > forced to cache=off, and then they claim specvirt is marketing, so for > > Xen it's better than nothing I guess. > > Surely Xen can use the pagecache, it uses Linux for I/O just like kvm. > > > I'm trying right now to evaluate it as a pure zcache host side > > optimization. > > zcache style usage is fine. It's purely internal so no ABI constraints, > and no hypercalls either. It's still synchronous though so RAMster like > approaches will not work well. Still experimental, but only the initial local put must be synchronous. RAMster uses a separate thread to "remotify" pre-compressed pages. The "get" still needs to be synchronous, but (if I ever have time to get back to coding it) I've got some ideas on how to fix that. If I manage to get that working, perhaps it could be used for Andrea's write-precompressed-zcache-pages-to-disk. Dan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href