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xen/balloon: use a kernel thread instead a workqueue

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Today the Xen ballooning is done via delayed work in a workqueue. This
might result in workqueue hangups being reported in case of large
amounts of memory are being ballooned in one go (here 16GB):

BUG: workqueue lockup - pool cpus=6 node=0 flags=0x0 nice=0 stuck for 64s!
Showing busy workqueues and worker pools:
workqueue events: flags=0x0
  pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=2/256 refcnt=3
    in-flight: 229:balloon_process
    pending: cache_reap
workqueue events_freezable_power_: flags=0x84
  pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    pending: disk_events_workfn
workqueue mm_percpu_wq: flags=0x8
  pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
    pending: vmstat_update
pool 12: cpus=6 node=0 flags=0x0 nice=0 hung=64s workers=3 idle: 2222 43

This can easily be avoided by using a dedicated kernel thread for doing
the ballooning work.

Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210827123206.15429-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2021-08-27 14:32:06 +02:00
parent 58e636039b
commit 8480ed9c2b
1 changed files with 45 additions and 17 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

62
drivers/xen/balloon.c
View file

@ -43,6 +43,8 @@
#include <linux/sched.h>
#include <linux/cred.h>
#include <linux/errno.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/mm.h>
#include <linux/memblock.h>
#include <linux/pagemap.h>
@ -115,7 +117,7 @@ static struct ctl_table xen_root[] = {
#define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
/*
* balloon_process() state:
* balloon_thread() state:
*
* BP_DONE: done or nothing to do,
* BP_WAIT: wait to be rescheduled,
@ -130,6 +132,8 @@ enum bp_state {
BP_ECANCELED
};
/* Main waiting point for xen-balloon thread. */
static DECLARE_WAIT_QUEUE_HEAD(balloon_thread_wq);
static DEFINE_MUTEX(balloon_mutex);
@ -144,10 +148,6 @@ static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
static LIST_HEAD(ballooned_pages);
static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
/* Main work function, always executed in process context. */
static void balloon_process(struct work_struct *work);
static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
/* When ballooning out (allocating memory to return to Xen) we don't really
want the kernel to try too hard since that can trigger the oom killer. */
#define GFP_BALLOON \
@ -366,7 +366,7 @@ static void xen_online_page(struct page *page, unsigned int order)
static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
{
if (val == MEM_ONLINE)
schedule_delayed_work(&balloon_worker, 0);
wake_up(&balloon_thread_wq);
return NOTIFY_OK;
}
@ -491,18 +491,43 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
}
/*
* As this is a work item it is guaranteed to run as a single instance only.
* Stop waiting if either state is not BP_EAGAIN and ballooning action is
* needed, or if the credit has changed while state is BP_EAGAIN.
*/
static bool balloon_thread_cond(enum bp_state state, long credit)
{
if (state != BP_EAGAIN)
credit = 0;
return current_credit() != credit || kthread_should_stop();
}
/*
* As this is a kthread it is guaranteed to run as a single instance only.
* We may of course race updates of the target counts (which are protected
* by the balloon lock), or with changes to the Xen hard limit, but we will
* recover from these in time.
*/
static void balloon_process(struct work_struct *work)
static int balloon_thread(void *unused)
{
enum bp_state state = BP_DONE;
long credit;
unsigned long timeout;
set_freezable();
for (;;) {
if (state == BP_EAGAIN)
timeout = balloon_stats.schedule_delay * HZ;
else
timeout = 3600 * HZ;
credit = current_credit();
wait_event_interruptible_timeout(balloon_thread_wq,
balloon_thread_cond(state, credit), timeout);
if (kthread_should_stop())
return 0;
do {
mutex_lock(&balloon_mutex);
credit = current_credit();
@ -529,12 +554,7 @@ static void balloon_process(struct work_struct *work)
mutex_unlock(&balloon_mutex);
cond_resched();
} while (credit && state == BP_DONE);
/* Schedule more work if there is some still to be done. */
if (state == BP_EAGAIN)
schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
}
}
/* Resets the Xen limit, sets new target, and kicks off processing. */
@ -542,7 +562,7 @@ void balloon_set_new_target(unsigned long target)
{
/* No need for lock. Not read-modify-write updates. */
balloon_stats.target_pages = target;
schedule_delayed_work(&balloon_worker, 0);
wake_up(&balloon_thread_wq);
}
EXPORT_SYMBOL_GPL(balloon_set_new_target);
@ -647,7 +667,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
/* The balloon may be too large now. Shrink it if needed. */
if (current_credit())
schedule_delayed_work(&balloon_worker, 0);
wake_up(&balloon_thread_wq);
mutex_unlock(&balloon_mutex);
}
@ -679,6 +699,8 @@ static void __init balloon_add_region(unsigned long start_pfn,
static int __init balloon_init(void)
{
struct task_struct *task;
if (!xen_domain())
return -ENODEV;
@ -722,6 +744,12 @@ static int __init balloon_init(void)
}
#endif
task = kthread_run(balloon_thread, NULL, "xen-balloon");
if (IS_ERR(task)) {
pr_err("xen-balloon thread could not be started, ballooning will not work!\n");
return PTR_ERR(task);
}
/* Init the xen-balloon driver. */
xen_balloon_init();