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Keir Fraser
78c4e40239
and monitor tool This patch adds tmem support to the largely unknown/unused xenballoond scripts that implement both self-ballooning and a foundation for directed-ballooning. Tmem and automated ballooning are highly complementary in that, when ballooning is over-aggressive, paging and swapping can increase noticably. Precache preserves evicted pages that may be needed again soon (thus eliminating disk reads) and preswap provides memory-based swapping that occurs if ballooning is insufficiently responsive to a sudden increase in activity and memory demand (thus eliminating disk writes and reads). There are two changes in this patch: 1) The xenballoond service is a convenient place to implement userland "preswap shrinking".** 2) The xenballoon-monitor script is a convenient place to report (and view with "watch -d") the frequent memory rebalancing that results from tmem usage on a busy system. Note that for best results (and for the monitor script to work), the xenstore-* tools should be installed on each guest. (** In a disk-based swap device, stale pages are often left on-disk even after they are no longer needed or valid; they are simply overwritten if/when the disk blocks are needed again, which may be a very long time. Preswap behaves much like a disk, but uses precious pages of memory that count against a guest's memory allocation; thus stale pages are very undesirable. Preswap shrinking periodically attempts to remove stale pages from preswap by using a sysfs interface created by the linux-side tmem patch.) Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>