--- /dev/null
+/******************************************************************************
+ * Xen selfballoon driver (and optional frontswap self-shrinking driver)
+ *
+ * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
+ *
+ * This code complements the cleancache and frontswap patchsets to optimize
+ * support for Xen Transcendent Memory ("tmem"). The policy it implements
+ * is rudimentary and will likely improve over time, but it does work well
+ * enough today.
+ *
+ * Two functionalities are implemented here which both use "control theory"
+ * (feedback) to optimize memory utilization. In a virtualized environment
+ * such as Xen, RAM is often a scarce resource and we would like to ensure
+ * that each of a possibly large number of virtual machines is using RAM
+ * efficiently, i.e. using as little as possible when under light load
+ * and obtaining as much as possible when memory demands are high.
+ * Since RAM needs vary highly dynamically and sometimes dramatically,
+ * "hysteresis" is used, that is, memory target is determined not just
+ * on current data but also on past data stored in the system.
+ *
+ * "Selfballooning" creates memory pressure by managing the Xen balloon
+ * driver to decrease and increase available kernel memory, driven
+ * largely by the target value of "Committed_AS" (see /proc/meminfo).
+ * Since Committed_AS does not account for clean mapped pages (i.e. pages
+ * in RAM that are identical to pages on disk), selfballooning has the
+ * affect of pushing less frequently used clean pagecache pages out of
+ * kernel RAM and, presumably using cleancache, into Xen tmem where
+ * Xen can more efficiently optimize RAM utilization for such pages.
+ *
+ * When kernel memory demand unexpectedly increases faster than Xen, via
+ * the selfballoon driver, is able to (or chooses to) provide usable RAM,
+ * the kernel may invoke swapping. In most cases, frontswap is able
+ * to absorb this swapping into Xen tmem. However, due to the fact
+ * that the kernel swap subsystem assumes swapping occurs to a disk,
+ * swapped pages may sit on the disk for a very long time; even if
+ * the kernel knows the page will never be used again. This is because
+ * the disk space costs very little and can be overwritten when
+ * necessary. When such stale pages are in frontswap, however, they
+ * are taking up valuable real estate. "Frontswap selfshrinking" works
+ * to resolve this: When frontswap activity is otherwise stable
+ * and the guest kernel is not under memory pressure, the "frontswap
+ * selfshrinking" accounts for this by providing pressure to remove some
+ * pages from frontswap and return them to kernel memory.
+ *
+ * For both "selfballooning" and "frontswap-selfshrinking", a worker
+ * thread is used and sysfs tunables are provided to adjust the frequency
+ * and rate of adjustments to achieve the goal, as well as to disable one
+ * or both functions independently.
+ *
+ * While some argue that this functionality can and should be implemented
+ * in userspace, it has been observed that bad things happen (e.g. OOMs).
+ *
+ * System configuration note: Selfballooning should not be enabled on
+ * systems without a sufficiently large swap device configured; for best
+ * results, it is recommended that total swap be increased by the size
+ * of the guest memory. Note, that selfballooning should be disabled by default
+ * if frontswap is not configured. Similarly selfballooning should be enabled
+ * by default if frontswap is configured and can be disabled with the
+ * "tmem.selfballooning=0" kernel boot option. Finally, when frontswap is
+ * configured, frontswap-selfshrinking can be disabled with the
+ * "tmem.selfshrink=0" kernel boot option.
+ *
+ * Selfballooning is disallowed in domain0 and force-disabled.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/bootmem.h>
+#include <linux/swap.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/module.h>
+#include <linux/workqueue.h>
+#include <linux/device.h>
+#include <xen/balloon.h>
+#include <xen/tmem.h>
+#include <xen/xen.h>
+
+/* Enable/disable with sysfs. */
+static int xen_selfballooning_enabled __read_mostly;
+
+/*
+ * Controls rate at which memory target (this iteration) approaches
+ * ultimate goal when memory need is increasing (up-hysteresis) or
+ * decreasing (down-hysteresis). Higher values of hysteresis cause
+ * slower increases/decreases. The default values for the various
+ * parameters were deemed reasonable by experimentation, may be
+ * workload-dependent, and can all be adjusted via sysfs.
+ */
+static unsigned int selfballoon_downhysteresis __read_mostly = 8;
+static unsigned int selfballoon_uphysteresis __read_mostly = 1;
+
+/* In HZ, controls frequency of worker invocation. */
+static unsigned int selfballoon_interval __read_mostly = 5;
+
+/*
+ * Minimum usable RAM in MB for selfballooning target for balloon.
+ * If non-zero, it is added to totalreserve_pages and self-ballooning
+ * will not balloon below the sum. If zero, a piecewise linear function
+ * is calculated as a minimum and added to totalreserve_pages. Note that
+ * setting this value indiscriminately may cause OOMs and crashes.
+ */
+static unsigned int selfballoon_min_usable_mb;
+
+/*
+ * Amount of RAM in MB to add to the target number of pages.
+ * Can be used to reserve some more room for caches and the like.
+ */
+static unsigned int selfballoon_reserved_mb;
+
+static void selfballoon_process(struct work_struct *work);
+static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
+
+#ifdef CONFIG_FRONTSWAP
+#include <linux/frontswap.h>
+
+/* Enable/disable with sysfs. */
+static bool frontswap_selfshrinking __read_mostly;
+
+/*
+ * The default values for the following parameters were deemed reasonable
+ * by experimentation, may be workload-dependent, and can all be
+ * adjusted via sysfs.
+ */
+
+/* Control rate for frontswap shrinking. Higher hysteresis is slower. */
+static unsigned int frontswap_hysteresis __read_mostly = 20;
+
+/*
+ * Number of selfballoon worker invocations to wait before observing that
+ * frontswap selfshrinking should commence. Note that selfshrinking does
+ * not use a separate worker thread.
+ */
+static unsigned int frontswap_inertia __read_mostly = 3;
+
+/* Countdown to next invocation of frontswap_shrink() */
+static unsigned long frontswap_inertia_counter;
+
+/*
+ * Invoked by the selfballoon worker thread, uses current number of pages
+ * in frontswap (frontswap_curr_pages()), previous status, and control
+ * values (hysteresis and inertia) to determine if frontswap should be
+ * shrunk and what the new frontswap size should be. Note that
+ * frontswap_shrink is essentially a partial swapoff that immediately
+ * transfers pages from the "swap device" (frontswap) back into kernel
+ * RAM; despite the name, frontswap "shrinking" is very different from
+ * the "shrinker" interface used by the kernel MM subsystem to reclaim
+ * memory.
+ */
+static void frontswap_selfshrink(void)
+{
+ static unsigned long cur_frontswap_pages;
+ static unsigned long last_frontswap_pages;
+ static unsigned long tgt_frontswap_pages;
+
+ last_frontswap_pages = cur_frontswap_pages;
+ cur_frontswap_pages = frontswap_curr_pages();
+ if (!cur_frontswap_pages ||
+ (cur_frontswap_pages > last_frontswap_pages)) {
+ frontswap_inertia_counter = frontswap_inertia;
+ return;
+ }
+ if (frontswap_inertia_counter && --frontswap_inertia_counter)
+ return;
+ if (cur_frontswap_pages <= frontswap_hysteresis)
+ tgt_frontswap_pages = 0;
+ else
+ tgt_frontswap_pages = cur_frontswap_pages -
+ (cur_frontswap_pages / frontswap_hysteresis);
+ frontswap_shrink(tgt_frontswap_pages);
+ frontswap_inertia_counter = frontswap_inertia;
+}
+
+#endif /* CONFIG_FRONTSWAP */
+
+#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
+#define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
+
+/*
+ * Use current balloon size, the goal (vm_committed_as), and hysteresis
+ * parameters to set a new target balloon size
+ */
+static void selfballoon_process(struct work_struct *work)
+{
+ unsigned long cur_pages, goal_pages, tgt_pages, floor_pages;
+ unsigned long useful_pages;
+ bool reset_timer = false;
+
+ if (xen_selfballooning_enabled) {
+ cur_pages = totalram_pages;
+ tgt_pages = cur_pages; /* default is no change */
+ goal_pages = vm_memory_committed() +
+ totalreserve_pages +
+ MB2PAGES(selfballoon_reserved_mb);
+#ifdef CONFIG_FRONTSWAP
+ /* allow space for frontswap pages to be repatriated */
+ if (frontswap_selfshrinking && frontswap_enabled)
+ goal_pages += frontswap_curr_pages();
+#endif
+ if (cur_pages > goal_pages)
+ tgt_pages = cur_pages -
+ ((cur_pages - goal_pages) /
+ selfballoon_downhysteresis);
+ else if (cur_pages < goal_pages)
+ tgt_pages = cur_pages +
+ ((goal_pages - cur_pages) /
+ selfballoon_uphysteresis);
+ /* else if cur_pages == goal_pages, no change */
+ useful_pages = max_pfn - totalreserve_pages;
+ if (selfballoon_min_usable_mb != 0)
+ floor_pages = totalreserve_pages +
+ MB2PAGES(selfballoon_min_usable_mb);
+ /* piecewise linear function ending in ~3% slope */
+ else if (useful_pages < MB2PAGES(16))
+ floor_pages = max_pfn; /* not worth ballooning */
+ else if (useful_pages < MB2PAGES(64))
+ floor_pages = totalreserve_pages + MB2PAGES(16) +
+ ((useful_pages - MB2PAGES(16)) >> 1);
+ else if (useful_pages < MB2PAGES(512))
+ floor_pages = totalreserve_pages + MB2PAGES(40) +
+ ((useful_pages - MB2PAGES(40)) >> 3);
+ else /* useful_pages >= MB2PAGES(512) */
+ floor_pages = totalreserve_pages + MB2PAGES(99) +
+ ((useful_pages - MB2PAGES(99)) >> 5);
+ if (tgt_pages < floor_pages)
+ tgt_pages = floor_pages;
+ balloon_set_new_target(tgt_pages +
+ balloon_stats.current_pages - totalram_pages);
+ reset_timer = true;
+ }
+#ifdef CONFIG_FRONTSWAP
+ if (frontswap_selfshrinking && frontswap_enabled) {
+ frontswap_selfshrink();
+ reset_timer = true;
+ }
+#endif
+ if (reset_timer)
+ schedule_delayed_work(&selfballoon_worker,
+ selfballoon_interval * HZ);
+}
+
+#ifdef CONFIG_SYSFS
+
+#include <linux/capability.h>
+
+#define SELFBALLOON_SHOW(name, format, args...) \
+ static ssize_t show_##name(struct device *dev, \
+ struct device_attribute *attr, \
+ char *buf) \
+ { \
+ return sprintf(buf, format, ##args); \
+ }
+
+SELFBALLOON_SHOW(selfballooning, "%d\n", xen_selfballooning_enabled);
+
+static ssize_t store_selfballooning(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ bool was_enabled = xen_selfballooning_enabled;
+ unsigned long tmp;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ err = kstrtoul(buf, 10, &tmp);
+ if (err)
+ return err;
+ if ((tmp != 0) && (tmp != 1))
+ return -EINVAL;
+
+ xen_selfballooning_enabled = !!tmp;
+ if (!was_enabled && xen_selfballooning_enabled)
+ schedule_delayed_work(&selfballoon_worker,
+ selfballoon_interval * HZ);
+
+ return count;
+}
+
+static DEVICE_ATTR(selfballooning, S_IRUGO | S_IWUSR,
+ show_selfballooning, store_selfballooning);
+
+SELFBALLOON_SHOW(selfballoon_interval, "%d\n", selfballoon_interval);
+
+static ssize_t store_selfballoon_interval(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ selfballoon_interval = val;
+ return count;
+}
+
+static DEVICE_ATTR(selfballoon_interval, S_IRUGO | S_IWUSR,
+ show_selfballoon_interval, store_selfballoon_interval);
+
+SELFBALLOON_SHOW(selfballoon_downhys, "%d\n", selfballoon_downhysteresis);
+
+static ssize_t store_selfballoon_downhys(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ selfballoon_downhysteresis = val;
+ return count;
+}
+
+static DEVICE_ATTR(selfballoon_downhysteresis, S_IRUGO | S_IWUSR,
+ show_selfballoon_downhys, store_selfballoon_downhys);
+
+
+SELFBALLOON_SHOW(selfballoon_uphys, "%d\n", selfballoon_uphysteresis);
+
+static ssize_t store_selfballoon_uphys(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ selfballoon_uphysteresis = val;
+ return count;
+}
+
+static DEVICE_ATTR(selfballoon_uphysteresis, S_IRUGO | S_IWUSR,
+ show_selfballoon_uphys, store_selfballoon_uphys);
+
+SELFBALLOON_SHOW(selfballoon_min_usable_mb, "%d\n",
+ selfballoon_min_usable_mb);
+
+static ssize_t store_selfballoon_min_usable_mb(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ selfballoon_min_usable_mb = val;
+ return count;
+}
+
+static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
+ show_selfballoon_min_usable_mb,
+ store_selfballoon_min_usable_mb);
+
+SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
+ selfballoon_reserved_mb);
+
+static ssize_t store_selfballoon_reserved_mb(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ selfballoon_reserved_mb = val;
+ return count;
+}
+
+static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
+ show_selfballoon_reserved_mb,
+ store_selfballoon_reserved_mb);
+
+
+#ifdef CONFIG_FRONTSWAP
+SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
+
+static ssize_t store_frontswap_selfshrinking(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ bool was_enabled = frontswap_selfshrinking;
+ unsigned long tmp;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &tmp);
+ if (err)
+ return err;
+ if ((tmp != 0) && (tmp != 1))
+ return -EINVAL;
+ frontswap_selfshrinking = !!tmp;
+ if (!was_enabled && !xen_selfballooning_enabled &&
+ frontswap_selfshrinking)
+ schedule_delayed_work(&selfballoon_worker,
+ selfballoon_interval * HZ);
+
+ return count;
+}
+
+static DEVICE_ATTR(frontswap_selfshrinking, S_IRUGO | S_IWUSR,
+ show_frontswap_selfshrinking, store_frontswap_selfshrinking);
+
+SELFBALLOON_SHOW(frontswap_inertia, "%d\n", frontswap_inertia);
+
+static ssize_t store_frontswap_inertia(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ frontswap_inertia = val;
+ frontswap_inertia_counter = val;
+ return count;
+}
+
+static DEVICE_ATTR(frontswap_inertia, S_IRUGO | S_IWUSR,
+ show_frontswap_inertia, store_frontswap_inertia);
+
+SELFBALLOON_SHOW(frontswap_hysteresis, "%d\n", frontswap_hysteresis);
+
+static ssize_t store_frontswap_hysteresis(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ unsigned long val;
+ int err;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return err;
+ if (val == 0)
+ return -EINVAL;
+ frontswap_hysteresis = val;
+ return count;
+}
+
+static DEVICE_ATTR(frontswap_hysteresis, S_IRUGO | S_IWUSR,
+ show_frontswap_hysteresis, store_frontswap_hysteresis);
+
+#endif /* CONFIG_FRONTSWAP */
+
+static struct attribute *selfballoon_attrs[] = {
+ &dev_attr_selfballooning.attr,
+ &dev_attr_selfballoon_interval.attr,
+ &dev_attr_selfballoon_downhysteresis.attr,
+ &dev_attr_selfballoon_uphysteresis.attr,
+ &dev_attr_selfballoon_min_usable_mb.attr,
+ &dev_attr_selfballoon_reserved_mb.attr,
+#ifdef CONFIG_FRONTSWAP
+ &dev_attr_frontswap_selfshrinking.attr,
+ &dev_attr_frontswap_hysteresis.attr,
+ &dev_attr_frontswap_inertia.attr,
+#endif
+ NULL
+};
+
+static const struct attribute_group selfballoon_group = {
+ .name = "selfballoon",
+ .attrs = selfballoon_attrs
+};
+#endif
+
+int register_xen_selfballooning(struct device *dev)
+{
+ int error = -1;
+
+#ifdef CONFIG_SYSFS
+ error = sysfs_create_group(&dev->kobj, &selfballoon_group);
+#endif
+ return error;
+}
+EXPORT_SYMBOL(register_xen_selfballooning);
+
+int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
+{
+ bool enable = false;
+ unsigned long reserve_pages;
+
+ if (!xen_domain())
+ return -ENODEV;
+
+ if (xen_initial_domain()) {
+ pr_info("Xen selfballooning driver disabled for domain0\n");
+ return -ENODEV;
+ }
+
+ xen_selfballooning_enabled = tmem_enabled && use_selfballooning;
+ if (xen_selfballooning_enabled) {
+ pr_info("Initializing Xen selfballooning driver\n");
+ enable = true;
+ }
+#ifdef CONFIG_FRONTSWAP
+ frontswap_selfshrinking = tmem_enabled && use_frontswap_selfshrink;
+ if (frontswap_selfshrinking) {
+ pr_info("Initializing frontswap selfshrinking driver\n");
+ enable = true;
+ }
+#endif
+ if (!enable)
+ return -ENODEV;
+
+ /*
+ * Give selfballoon_reserved_mb a default value(10% of total ram pages)
+ * to make selfballoon not so aggressive.
+ *
+ * There are mainly two reasons:
+ * 1) The original goal_page didn't consider some pages used by kernel
+ * space, like slab pages and memory used by device drivers.
+ *
+ * 2) The balloon driver may not give back memory to guest OS fast
+ * enough when the workload suddenly aquries a lot of physical memory.
+ *
+ * In both cases, the guest OS will suffer from memory pressure and
+ * OOM killer may be triggered.
+ * By reserving extra 10% of total ram pages, we can keep the system
+ * much more reliably and response faster in some cases.
+ */
+ if (!selfballoon_reserved_mb) {
+ reserve_pages = totalram_pages / 10;
+ selfballoon_reserved_mb = PAGES2MB(reserve_pages);
+ }
+ schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
+
+ return 0;
+}
+EXPORT_SYMBOL(xen_selfballoon_init);
Code Review / kvmfornfv.git / blobdiff