1 /******************************************************************************
2 * Xen selfballoon driver (and optional frontswap self-shrinking driver)
4 * Copyright (c) 2009-2011, Dan Magenheimer, Oracle Corp.
6 * This code complements the cleancache and frontswap patchsets to optimize
7 * support for Xen Transcendent Memory ("tmem"). The policy it implements
8 * is rudimentary and will likely improve over time, but it does work well
11 * Two functionalities are implemented here which both use "control theory"
12 * (feedback) to optimize memory utilization. In a virtualized environment
13 * such as Xen, RAM is often a scarce resource and we would like to ensure
14 * that each of a possibly large number of virtual machines is using RAM
15 * efficiently, i.e. using as little as possible when under light load
16 * and obtaining as much as possible when memory demands are high.
17 * Since RAM needs vary highly dynamically and sometimes dramatically,
18 * "hysteresis" is used, that is, memory target is determined not just
19 * on current data but also on past data stored in the system.
21 * "Selfballooning" creates memory pressure by managing the Xen balloon
22 * driver to decrease and increase available kernel memory, driven
23 * largely by the target value of "Committed_AS" (see /proc/meminfo).
24 * Since Committed_AS does not account for clean mapped pages (i.e. pages
25 * in RAM that are identical to pages on disk), selfballooning has the
26 * affect of pushing less frequently used clean pagecache pages out of
27 * kernel RAM and, presumably using cleancache, into Xen tmem where
28 * Xen can more efficiently optimize RAM utilization for such pages.
30 * When kernel memory demand unexpectedly increases faster than Xen, via
31 * the selfballoon driver, is able to (or chooses to) provide usable RAM,
32 * the kernel may invoke swapping. In most cases, frontswap is able
33 * to absorb this swapping into Xen tmem. However, due to the fact
34 * that the kernel swap subsystem assumes swapping occurs to a disk,
35 * swapped pages may sit on the disk for a very long time; even if
36 * the kernel knows the page will never be used again. This is because
37 * the disk space costs very little and can be overwritten when
38 * necessary. When such stale pages are in frontswap, however, they
39 * are taking up valuable real estate. "Frontswap selfshrinking" works
40 * to resolve this: When frontswap activity is otherwise stable
41 * and the guest kernel is not under memory pressure, the "frontswap
42 * selfshrinking" accounts for this by providing pressure to remove some
43 * pages from frontswap and return them to kernel memory.
45 * For both "selfballooning" and "frontswap-selfshrinking", a worker
46 * thread is used and sysfs tunables are provided to adjust the frequency
47 * and rate of adjustments to achieve the goal, as well as to disable one
48 * or both functions independently.
50 * While some argue that this functionality can and should be implemented
51 * in userspace, it has been observed that bad things happen (e.g. OOMs).
53 * System configuration note: Selfballooning should not be enabled on
54 * systems without a sufficiently large swap device configured; for best
55 * results, it is recommended that total swap be increased by the size
56 * of the guest memory. Note, that selfballooning should be disabled by default
57 * if frontswap is not configured. Similarly selfballooning should be enabled
58 * by default if frontswap is configured and can be disabled with the
59 * "tmem.selfballooning=0" kernel boot option. Finally, when frontswap is
60 * configured, frontswap-selfshrinking can be disabled with the
61 * "tmem.selfshrink=0" kernel boot option.
63 * Selfballooning is disallowed in domain0 and force-disabled.
67 #include <linux/kernel.h>
68 #include <linux/bootmem.h>
69 #include <linux/swap.h>
71 #include <linux/mman.h>
72 #include <linux/module.h>
73 #include <linux/workqueue.h>
74 #include <linux/device.h>
75 #include <xen/balloon.h>
79 /* Enable/disable with sysfs. */
80 static int xen_selfballooning_enabled __read_mostly
;
83 * Controls rate at which memory target (this iteration) approaches
84 * ultimate goal when memory need is increasing (up-hysteresis) or
85 * decreasing (down-hysteresis). Higher values of hysteresis cause
86 * slower increases/decreases. The default values for the various
87 * parameters were deemed reasonable by experimentation, may be
88 * workload-dependent, and can all be adjusted via sysfs.
90 static unsigned int selfballoon_downhysteresis __read_mostly
= 8;
91 static unsigned int selfballoon_uphysteresis __read_mostly
= 1;
93 /* In HZ, controls frequency of worker invocation. */
94 static unsigned int selfballoon_interval __read_mostly
= 5;
97 * Minimum usable RAM in MB for selfballooning target for balloon.
98 * If non-zero, it is added to totalreserve_pages and self-ballooning
99 * will not balloon below the sum. If zero, a piecewise linear function
100 * is calculated as a minimum and added to totalreserve_pages. Note that
101 * setting this value indiscriminately may cause OOMs and crashes.
103 static unsigned int selfballoon_min_usable_mb
;
106 * Amount of RAM in MB to add to the target number of pages.
107 * Can be used to reserve some more room for caches and the like.
109 static unsigned int selfballoon_reserved_mb
;
111 static void selfballoon_process(struct work_struct
*work
);
112 static DECLARE_DELAYED_WORK(selfballoon_worker
, selfballoon_process
);
114 #ifdef CONFIG_FRONTSWAP
115 #include <linux/frontswap.h>
117 /* Enable/disable with sysfs. */
118 static bool frontswap_selfshrinking __read_mostly
;
121 * The default values for the following parameters were deemed reasonable
122 * by experimentation, may be workload-dependent, and can all be
123 * adjusted via sysfs.
126 /* Control rate for frontswap shrinking. Higher hysteresis is slower. */
127 static unsigned int frontswap_hysteresis __read_mostly
= 20;
130 * Number of selfballoon worker invocations to wait before observing that
131 * frontswap selfshrinking should commence. Note that selfshrinking does
132 * not use a separate worker thread.
134 static unsigned int frontswap_inertia __read_mostly
= 3;
136 /* Countdown to next invocation of frontswap_shrink() */
137 static unsigned long frontswap_inertia_counter
;
140 * Invoked by the selfballoon worker thread, uses current number of pages
141 * in frontswap (frontswap_curr_pages()), previous status, and control
142 * values (hysteresis and inertia) to determine if frontswap should be
143 * shrunk and what the new frontswap size should be. Note that
144 * frontswap_shrink is essentially a partial swapoff that immediately
145 * transfers pages from the "swap device" (frontswap) back into kernel
146 * RAM; despite the name, frontswap "shrinking" is very different from
147 * the "shrinker" interface used by the kernel MM subsystem to reclaim
150 static void frontswap_selfshrink(void)
152 static unsigned long cur_frontswap_pages
;
153 static unsigned long last_frontswap_pages
;
154 static unsigned long tgt_frontswap_pages
;
156 last_frontswap_pages
= cur_frontswap_pages
;
157 cur_frontswap_pages
= frontswap_curr_pages();
158 if (!cur_frontswap_pages
||
159 (cur_frontswap_pages
> last_frontswap_pages
)) {
160 frontswap_inertia_counter
= frontswap_inertia
;
163 if (frontswap_inertia_counter
&& --frontswap_inertia_counter
)
165 if (cur_frontswap_pages
<= frontswap_hysteresis
)
166 tgt_frontswap_pages
= 0;
168 tgt_frontswap_pages
= cur_frontswap_pages
-
169 (cur_frontswap_pages
/ frontswap_hysteresis
);
170 frontswap_shrink(tgt_frontswap_pages
);
173 #endif /* CONFIG_FRONTSWAP */
175 #define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
178 * Use current balloon size, the goal (vm_committed_as), and hysteresis
179 * parameters to set a new target balloon size
181 static void selfballoon_process(struct work_struct
*work
)
183 unsigned long cur_pages
, goal_pages
, tgt_pages
, floor_pages
;
184 unsigned long useful_pages
;
185 bool reset_timer
= false;
187 if (xen_selfballooning_enabled
) {
188 cur_pages
= totalram_pages
;
189 tgt_pages
= cur_pages
; /* default is no change */
190 goal_pages
= vm_memory_committed() +
192 MB2PAGES(selfballoon_reserved_mb
);
193 #ifdef CONFIG_FRONTSWAP
194 /* allow space for frontswap pages to be repatriated */
195 if (frontswap_selfshrinking
&& frontswap_enabled
)
196 goal_pages
+= frontswap_curr_pages();
198 if (cur_pages
> goal_pages
)
199 tgt_pages
= cur_pages
-
200 ((cur_pages
- goal_pages
) /
201 selfballoon_downhysteresis
);
202 else if (cur_pages
< goal_pages
)
203 tgt_pages
= cur_pages
+
204 ((goal_pages
- cur_pages
) /
205 selfballoon_uphysteresis
);
206 /* else if cur_pages == goal_pages, no change */
207 useful_pages
= max_pfn
- totalreserve_pages
;
208 if (selfballoon_min_usable_mb
!= 0)
209 floor_pages
= totalreserve_pages
+
210 MB2PAGES(selfballoon_min_usable_mb
);
211 /* piecewise linear function ending in ~3% slope */
212 else if (useful_pages
< MB2PAGES(16))
213 floor_pages
= max_pfn
; /* not worth ballooning */
214 else if (useful_pages
< MB2PAGES(64))
215 floor_pages
= totalreserve_pages
+ MB2PAGES(16) +
216 ((useful_pages
- MB2PAGES(16)) >> 1);
217 else if (useful_pages
< MB2PAGES(512))
218 floor_pages
= totalreserve_pages
+ MB2PAGES(40) +
219 ((useful_pages
- MB2PAGES(40)) >> 3);
220 else /* useful_pages >= MB2PAGES(512) */
221 floor_pages
= totalreserve_pages
+ MB2PAGES(99) +
222 ((useful_pages
- MB2PAGES(99)) >> 5);
223 if (tgt_pages
< floor_pages
)
224 tgt_pages
= floor_pages
;
225 balloon_set_new_target(tgt_pages
+
226 balloon_stats
.current_pages
- totalram_pages
);
229 #ifdef CONFIG_FRONTSWAP
230 if (frontswap_selfshrinking
&& frontswap_enabled
) {
231 frontswap_selfshrink();
236 schedule_delayed_work(&selfballoon_worker
,
237 selfballoon_interval
* HZ
);
242 #include <linux/capability.h>
244 #define SELFBALLOON_SHOW(name, format, args...) \
245 static ssize_t show_##name(struct device *dev, \
246 struct device_attribute *attr, \
249 return sprintf(buf, format, ##args); \
252 SELFBALLOON_SHOW(selfballooning
, "%d\n", xen_selfballooning_enabled
);
254 static ssize_t
store_selfballooning(struct device
*dev
,
255 struct device_attribute
*attr
,
259 bool was_enabled
= xen_selfballooning_enabled
;
263 if (!capable(CAP_SYS_ADMIN
))
266 err
= strict_strtoul(buf
, 10, &tmp
);
267 if (err
|| ((tmp
!= 0) && (tmp
!= 1)))
270 xen_selfballooning_enabled
= !!tmp
;
271 if (!was_enabled
&& xen_selfballooning_enabled
)
272 schedule_delayed_work(&selfballoon_worker
,
273 selfballoon_interval
* HZ
);
278 static DEVICE_ATTR(selfballooning
, S_IRUGO
| S_IWUSR
,
279 show_selfballooning
, store_selfballooning
);
281 SELFBALLOON_SHOW(selfballoon_interval
, "%d\n", selfballoon_interval
);
283 static ssize_t
store_selfballoon_interval(struct device
*dev
,
284 struct device_attribute
*attr
,
291 if (!capable(CAP_SYS_ADMIN
))
293 err
= strict_strtoul(buf
, 10, &val
);
296 selfballoon_interval
= val
;
300 static DEVICE_ATTR(selfballoon_interval
, S_IRUGO
| S_IWUSR
,
301 show_selfballoon_interval
, store_selfballoon_interval
);
303 SELFBALLOON_SHOW(selfballoon_downhys
, "%d\n", selfballoon_downhysteresis
);
305 static ssize_t
store_selfballoon_downhys(struct device
*dev
,
306 struct device_attribute
*attr
,
313 if (!capable(CAP_SYS_ADMIN
))
315 err
= strict_strtoul(buf
, 10, &val
);
318 selfballoon_downhysteresis
= val
;
322 static DEVICE_ATTR(selfballoon_downhysteresis
, S_IRUGO
| S_IWUSR
,
323 show_selfballoon_downhys
, store_selfballoon_downhys
);
326 SELFBALLOON_SHOW(selfballoon_uphys
, "%d\n", selfballoon_uphysteresis
);
328 static ssize_t
store_selfballoon_uphys(struct device
*dev
,
329 struct device_attribute
*attr
,
336 if (!capable(CAP_SYS_ADMIN
))
338 err
= strict_strtoul(buf
, 10, &val
);
341 selfballoon_uphysteresis
= val
;
345 static DEVICE_ATTR(selfballoon_uphysteresis
, S_IRUGO
| S_IWUSR
,
346 show_selfballoon_uphys
, store_selfballoon_uphys
);
348 SELFBALLOON_SHOW(selfballoon_min_usable_mb
, "%d\n",
349 selfballoon_min_usable_mb
);
351 static ssize_t
store_selfballoon_min_usable_mb(struct device
*dev
,
352 struct device_attribute
*attr
,
359 if (!capable(CAP_SYS_ADMIN
))
361 err
= strict_strtoul(buf
, 10, &val
);
364 selfballoon_min_usable_mb
= val
;
368 static DEVICE_ATTR(selfballoon_min_usable_mb
, S_IRUGO
| S_IWUSR
,
369 show_selfballoon_min_usable_mb
,
370 store_selfballoon_min_usable_mb
);
372 SELFBALLOON_SHOW(selfballoon_reserved_mb
, "%d\n",
373 selfballoon_reserved_mb
);
375 static ssize_t
store_selfballoon_reserved_mb(struct device
*dev
,
376 struct device_attribute
*attr
,
383 if (!capable(CAP_SYS_ADMIN
))
385 err
= strict_strtoul(buf
, 10, &val
);
388 selfballoon_reserved_mb
= val
;
392 static DEVICE_ATTR(selfballoon_reserved_mb
, S_IRUGO
| S_IWUSR
,
393 show_selfballoon_reserved_mb
,
394 store_selfballoon_reserved_mb
);
397 #ifdef CONFIG_FRONTSWAP
398 SELFBALLOON_SHOW(frontswap_selfshrinking
, "%d\n", frontswap_selfshrinking
);
400 static ssize_t
store_frontswap_selfshrinking(struct device
*dev
,
401 struct device_attribute
*attr
,
405 bool was_enabled
= frontswap_selfshrinking
;
409 if (!capable(CAP_SYS_ADMIN
))
411 err
= strict_strtoul(buf
, 10, &tmp
);
412 if (err
|| ((tmp
!= 0) && (tmp
!= 1)))
414 frontswap_selfshrinking
= !!tmp
;
415 if (!was_enabled
&& !xen_selfballooning_enabled
&&
416 frontswap_selfshrinking
)
417 schedule_delayed_work(&selfballoon_worker
,
418 selfballoon_interval
* HZ
);
423 static DEVICE_ATTR(frontswap_selfshrinking
, S_IRUGO
| S_IWUSR
,
424 show_frontswap_selfshrinking
, store_frontswap_selfshrinking
);
426 SELFBALLOON_SHOW(frontswap_inertia
, "%d\n", frontswap_inertia
);
428 static ssize_t
store_frontswap_inertia(struct device
*dev
,
429 struct device_attribute
*attr
,
436 if (!capable(CAP_SYS_ADMIN
))
438 err
= strict_strtoul(buf
, 10, &val
);
441 frontswap_inertia
= val
;
442 frontswap_inertia_counter
= val
;
446 static DEVICE_ATTR(frontswap_inertia
, S_IRUGO
| S_IWUSR
,
447 show_frontswap_inertia
, store_frontswap_inertia
);
449 SELFBALLOON_SHOW(frontswap_hysteresis
, "%d\n", frontswap_hysteresis
);
451 static ssize_t
store_frontswap_hysteresis(struct device
*dev
,
452 struct device_attribute
*attr
,
459 if (!capable(CAP_SYS_ADMIN
))
461 err
= strict_strtoul(buf
, 10, &val
);
464 frontswap_hysteresis
= val
;
468 static DEVICE_ATTR(frontswap_hysteresis
, S_IRUGO
| S_IWUSR
,
469 show_frontswap_hysteresis
, store_frontswap_hysteresis
);
471 #endif /* CONFIG_FRONTSWAP */
473 static struct attribute
*selfballoon_attrs
[] = {
474 &dev_attr_selfballooning
.attr
,
475 &dev_attr_selfballoon_interval
.attr
,
476 &dev_attr_selfballoon_downhysteresis
.attr
,
477 &dev_attr_selfballoon_uphysteresis
.attr
,
478 &dev_attr_selfballoon_min_usable_mb
.attr
,
479 &dev_attr_selfballoon_reserved_mb
.attr
,
480 #ifdef CONFIG_FRONTSWAP
481 &dev_attr_frontswap_selfshrinking
.attr
,
482 &dev_attr_frontswap_hysteresis
.attr
,
483 &dev_attr_frontswap_inertia
.attr
,
488 static const struct attribute_group selfballoon_group
= {
489 .name
= "selfballoon",
490 .attrs
= selfballoon_attrs
494 int register_xen_selfballooning(struct device
*dev
)
499 error
= sysfs_create_group(&dev
->kobj
, &selfballoon_group
);
503 EXPORT_SYMBOL(register_xen_selfballooning
);
505 int xen_selfballoon_init(bool use_selfballooning
, bool use_frontswap_selfshrink
)
512 if (xen_initial_domain()) {
513 pr_info("xen/balloon: Xen selfballooning driver "
514 "disabled for domain0.\n");
518 xen_selfballooning_enabled
= tmem_enabled
&& use_selfballooning
;
519 if (xen_selfballooning_enabled
) {
520 pr_info("xen/balloon: Initializing Xen "
521 "selfballooning driver.\n");
524 #ifdef CONFIG_FRONTSWAP
525 frontswap_selfshrinking
= tmem_enabled
&& use_frontswap_selfshrink
;
526 if (frontswap_selfshrinking
) {
527 pr_info("xen/balloon: Initializing frontswap "
528 "selfshrinking driver.\n");
535 schedule_delayed_work(&selfballoon_worker
, selfballoon_interval
* HZ
);
539 EXPORT_SYMBOL(xen_selfballoon_init
);