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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /mm/pdflush.c
downloadlinux-sh-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'mm/pdflush.c')
-rw-r--r--mm/pdflush.c228
1 files changed, 228 insertions, 0 deletions
diff --git a/mm/pdflush.c b/mm/pdflush.c
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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>
+
+
+/*
+ * 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;
+ 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();
+ if (try_to_freeze(PF_FREEZE)) {
+ spin_lock_irq(&pdflush_lock);
+ continue;
+ }
+
+ spin_lock_irq(&pdflush_lock);
+ if (!list_empty(&my_work->list)) {
+ printk("pdflush: bogus wakeup!\n");
+ my_work->fn = NULL;
+ continue;
+ }
+ if (my_work->fn == NULL) {
+ printk("pdflush: NULL work function\n");
+ continue;
+ }
+ spin_unlock_irq(&pdflush_lock);
+
+ (*my_work->fn)(my_work->arg0);
+
+ /*
+ * Thread creation: For how long have there been zero
+ * available threads?
+ */
+ if (jiffies - last_empty_jifs > 1 * HZ) {
+ /* unlocked list_empty() test is OK here */
+ if (list_empty(&pdflush_list)) {
+ /* unlocked test is OK here */
+ if (nr_pdflush_threads < MAX_PDFLUSH_THREADS)
+ start_one_pdflush_thread();
+ }
+ }
+
+ spin_lock_irq(&pdflush_lock);
+ my_work->fn = NULL;
+
+ /*
+ * Thread destruction: For how long has the sleepiest
+ * thread slept?
+ */
+ if (list_empty(&pdflush_list))
+ continue;
+ if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
+ continue;
+ pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
+ if (jiffies - pdf->when_i_went_to_sleep > 1 * HZ) {
+ /* Limit exit rate */
+ pdf->when_i_went_to_sleep = jiffies;
+ break; /* exeunt */
+ }
+ }
+ nr_pdflush_threads--;
+ spin_unlock_irq(&pdflush_lock);
+ return 0;
+}
+
+/*
+ * Of course, my_work wants to be just a local in __pdflush(). It is
+ * separated out in this manner to hopefully prevent the compiler from
+ * performing unfortunate optimisations against the auto variables. Because
+ * these are visible to other tasks and CPUs. (No problem has actually
+ * been observed. This is just paranoia).
+ */
+static int pdflush(void *dummy)
+{
+ struct pdflush_work my_work;
+
+ /*
+ * pdflush can spend a lot of time doing encryption via dm-crypt. We
+ * don't want to do that at keventd's priority.
+ */
+ set_user_nice(current, 0);
+ return __pdflush(&my_work);
+}
+
+/*
+ * Attempt to wake up a pdflush thread, and get it to do some work for you.
+ * Returns zero if it indeed managed to find a worker thread, and passed your
+ * payload to it.
+ */
+int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0)
+{
+ unsigned long flags;
+ int ret = 0;
+
+ if (fn == NULL)
+ BUG(); /* Hard to diagnose if it's deferred */
+
+ spin_lock_irqsave(&pdflush_lock, flags);
+ if (list_empty(&pdflush_list)) {
+ spin_unlock_irqrestore(&pdflush_lock, flags);
+ ret = -1;
+ } else {
+ struct pdflush_work *pdf;
+
+ pdf = list_entry(pdflush_list.next, struct pdflush_work, list);
+ list_del_init(&pdf->list);
+ if (list_empty(&pdflush_list))
+ last_empty_jifs = jiffies;
+ pdf->fn = fn;
+ pdf->arg0 = arg0;
+ wake_up_process(pdf->who);
+ spin_unlock_irqrestore(&pdflush_lock, flags);
+ }
+ return ret;
+}
+
+static void start_one_pdflush_thread(void)
+{
+ kthread_run(pdflush, NULL, "pdflush");
+}
+
+static int __init pdflush_init(void)
+{
+ int i;
+
+ for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
+ start_one_pdflush_thread();
+ return 0;
+}
+
+module_init(pdflush_init);