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