litmus-rt.git - The LITMUS^RT kernel.

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The LITMUS^RT kernel.

Bjoern Brandenburg

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er@sgi.com> 2006-01-08 04:00:47 -0500 committer Linus Torvalds <torvalds@g5.osdl.org> 2006-01-08 23:12:41 -0500 [PATCH] Swap Migration V5: PF_SWAPWRITE to allow writing to swap' href='/cgit/cgit.cgi/litmus-rt.git/commit/mm/pdflush.c?h=wip-nested-locking&id=930d915252edda7042c944ed3c30194a2f9fe163'>930d915252ed

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/*
 * mm/pdflush.c - worker threads for writing back filesystem data
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * 09Apr2002	akpm@zip.com.au
 *		Initial version
 * 29Feb2004	kaos@sgi.com
 *		Move worker thread creation to kthread to avoid chewing
 *		up stack space with nested calls to kernel_thread.
 */

#include <linux/sched.h>
#include <linux/list.h>
#include <linux/signal.h>
#include <linux/spinlock.h>
#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>		// Needed by writeback.h
#include <linux/writeback.h>	// Prototypes pdflush_operation()
#include <linux/kthread.h>
#include <linux/cpuset.h>
#include <linux/freezer.h>


/*
 * Minimum and maximum number of pdflush instances
 */
#define MIN_PDFLUSH_THREADS	2
#define MAX_PDFLUSH_THREADS	8

static void start_one_pdflush_thread(void);


/*
 * The pdflush threads are worker threads for writing back dirty data.
 * Ideally, we'd like one thread per active disk spindle.  But the disk
 * topology is very hard to divine at this level.   Instead, we take
 * care in various places to prevent more than one pdflush thread from
 * performing writeback against a single filesystem.  pdflush threads
 * have the PF_FLUSHER flag set in current->flags to aid in this.
 */

/*
 * All the pdflush threads.  Protected by pdflush_lock
 */
static LIST_HEAD(pdflush_list);
static DEFINE_SPINLOCK(pdflush_lock);

/*
 * The count of currently-running pdflush threads.  Protected
 * by pdflush_lock.
 *
 * Readable by sysctl, but not writable.  Published to userspace at
 * /proc/sys/vm/nr_pdflush_threads.
 */
int nr_pdflush_threads = 0;

/*
 * The time at which the pdflush thread pool last went empty
 */
static unsigned long last_empty_jifs;

/*
 * The pdflush thread.
 *
 * Thread pool management algorithm:
 * 
 * - The minimum and maximum number of pdflush instances are bound
 *   by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
 * 
 * - If there have been no idle pdflush instances for 1 second, create
 *   a new one.
 * 
 * - If the least-recently-went-to-sleep pdflush thread has been asleep
 *   for more than one second, terminate a thread.
 */

/*
 * A structure for passing work to a pdflush thread.  Also for passing
 * state information between pdflush threads.  Protected by pdflush_lock.
 */
struct pdflush_work {
	struct task_struct *who;	/* The thread */
	void (*fn)(unsigned long);	/* A callback function */
	unsigned long arg0;		/* An argument to the callback */
	struct list_head list;		/* On pdflush_list, when idle */
	unsigned long when_i_went_to_sleep;
};

static int __pdflush(struct pdflush_work *my_work)
{
	current->flags |= PF_FLUSHER | PF_SWAPWRITE;
	set_freezable();
	my_work->fn = NULL;
	my_work->who = current;
	INIT_LIST_HEAD(&my_work->list);

	spin_lock_irq(&pdflush_lock);
	nr_pdflush_threads++;
	for ( ; ; ) {
		struct pdflush_work *pdf;

		set_current_state(TASK_INTERRUPTIBLE);
		list_move(&my_work->list, &pdflush_list);
		my_work->when_i_went_to_sleep = jiffies;
		spin_unlock_irq(&pdflush_lock);
		schedule();
		try_to_freeze();
		spin_lock_irq(&pdflush_lock);
		if (!list_empty(&my_work->list)) {
			/*
			 * Someone woke us up, but without removing our control
			 * structure from the global list.  swsusp will do this
			 * in try_to_freeze()->refrigerator().  Handle it.
			 */
			my_work->fn = NULL;


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