On Thu, Aug 10, 2017 at 03:17:46PM -0400, Vivek Goyal wrote: > On Thu, Aug 10, 2017 at 09:11:59AM -0700, Matthew Wilcox wrote: > > On Thu, Aug 10, 2017 at 02:28:49PM +1000, Dave Chinner wrote: > > > If we scale this up to a container host which is using reflink trees > > > it's shared root images, there might be hundreds of copies of the > > > same data held in cache (i.e. one page per container). Given that > > > the filesystem knows that the underlying data extent is shared when > > > we go to read it, it's relatively easy to add mechanisms to the > > > filesystem to return the same page for all attempts to read the > > > from a shared extent from all inodes that share it. > > > > I agree the problem exists. Should we try to fix this problem, or > > should we steer people towards solutions which don't have this problem? > > The solutions I've been seeing use COW block devices instead of COW > > filesystems, and DAX to share the common pages between the host and > > each guest. > > Hi Matthew, > > This is in the context of clear containers? It would be good to have > a solution for those who are not launching virt guests. > > overlayfs helps mitigate this page cache sharing issue but xfs reflink > and dm thin pool continue to face this issue. Right, this is with clear containers. But there's no reason it couldn't be used with other virtualisation solutions. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
