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Subject[patch] replace kupdate and bdflush with pdflush
Pretty simple.

- use a timer to kick off a pdflush thread every five seconds
to run the kupdate code.

- wakeup_bdflush() kicks off a pdflush thread to run the current
bdflush function.

There's some loss of functionality here - the ability to tune
the writeback periods. The numbers are hardwired at present.
But the intent is that buffer-based writeback disappears
altogether. New mechanisms for tuning the writeback will
need to be introduced.


Patch against 2.5.8-pre3+ratcache+readahead+pageprivate+pdflush+pdflush_inodes


--- 2.5.8-pre3/fs/buffer.c~dallocbase-50-pdflush_buffers Tue Apr 9 22:42:56 2002
+++ 2.5.8-pre3-akpm/fs/buffer.c Tue Apr 9 22:42:56 2002
@@ -46,7 +46,6 @@
#include <linux/iobuf.h>
#include <linux/highmem.h>
#include <linux/module.h>
-#include <linux/completion.h>
#include <linux/compiler.h>

#include <asm/uaccess.h>
@@ -2603,21 +2602,6 @@ void __init buffer_init(unsigned long me

}

-
-/* ====================== bdflush support =================== */
-
-/* This is a simple kernel daemon, whose job it is to provide a dynamic
- * response to dirty buffers. Once this process is activated, we write back
- * a limited number of buffers to the disks and then go back to sleep again.
- */
-
-DECLARE_WAIT_QUEUE_HEAD(bdflush_wait);
-
-void wakeup_bdflush(void)
-{
- wake_up_interruptible(&bdflush_wait);
-}
-
/*
* Here we attempt to write back old buffers. We also try to flush inodes
* and supers as well, since this function is essentially "update", and
@@ -2626,7 +2610,7 @@ void wakeup_bdflush(void)
* and superblocks so that we could write back only the old ones as well
*/

-static int sync_old_buffers(void)
+static void sync_old_buffers(unsigned long dummy)
{
lock_kernel();
sync_unlocked_inodes();
@@ -2642,10 +2626,9 @@ static int sync_old_buffers(void)
break;
if (write_some_buffers(NULL))
continue;
- return 0;
+ return;
}
spin_unlock(&lru_list_lock);
- return 0;
}

int block_sync_page(struct page *page)
@@ -2707,112 +2690,45 @@ asmlinkage long sys_bdflush(int func, lo
return 0;
}

-/*
- * This is the actual bdflush daemon itself. It used to be started from
- * the syscall above, but now we launch it ourselves internally with
- * kernel_thread(...) directly after the first thread in init/main.c
- */
-int bdflush(void *startup)
+static void bdflush(unsigned long pexclude)
{
- struct task_struct *tsk = current;
-
- /*
- * We have a bare-bones task_struct, and really should fill
- * in a few more things so "top" and /proc/2/{exe,root,cwd}
- * display semi-sane things. Not real crucial though...
- */
-
- tsk->session = 1;
- tsk->pgrp = 1;
- strcpy(tsk->comm, "bdflush");
-
- /* avoid getting signals */
- spin_lock_irq(&tsk->sigmask_lock);
- flush_signals(tsk);
- sigfillset(&tsk->blocked);
- recalc_sigpending();
- spin_unlock_irq(&tsk->sigmask_lock);
-
- complete((struct completion *)startup);
-
- for (;;) {
- CHECK_EMERGENCY_SYNC
-
+ while (balance_dirty_state() >= 0) {
spin_lock(&lru_list_lock);
- if (!write_some_buffers(NULL) || balance_dirty_state() < 0) {
- wait_for_some_buffers(NULL);
- interruptible_sleep_on(&bdflush_wait);
- }
+ if (write_some_buffers(NULL) == 0)
+ break;
}
+ clear_bit(0, (unsigned long *)pexclude);
}

-/*
- * This is the kernel update daemon. It was used to live in userspace
- * but since it's need to run safely we want it unkillable by mistake.
- * You don't need to change your userspace configuration since
- * the userspace `update` will do_exit(0) at the first sys_bdflush().
- */
-int kupdate(void *startup)
+void wakeup_bdflush(void)
{
- struct task_struct * tsk = current;
- int interval;
-
- tsk->session = 1;
- tsk->pgrp = 1;
- strcpy(tsk->comm, "kupdated");
-
- /* sigstop and sigcont will stop and wakeup kupdate */
- spin_lock_irq(&tsk->sigmask_lock);
- sigfillset(&tsk->blocked);
- siginitsetinv(&current->blocked, sigmask(SIGCONT) | sigmask(SIGSTOP));
- recalc_sigpending();
- spin_unlock_irq(&tsk->sigmask_lock);
+ static unsigned long exclude;

- complete((struct completion *)startup);
-
- for (;;) {
- wait_for_some_buffers(NULL);
-
- /* update interval */
- interval = bdf_prm.b_un.interval;
- if (interval) {
- tsk->state = TASK_INTERRUPTIBLE;
- schedule_timeout(interval);
- } else {
- stop_kupdate:
- tsk->state = TASK_STOPPED;
- schedule(); /* wait for SIGCONT */
- }
- /* check for sigstop */
- if (signal_pending(tsk)) {
- int stopped = 0;
- spin_lock_irq(&tsk->sigmask_lock);
- if (sigismember(&tsk->pending.signal, SIGSTOP)) {
- sigdelset(&tsk->pending.signal, SIGSTOP);
- stopped = 1;
- }
- recalc_sigpending();
- spin_unlock_irq(&tsk->sigmask_lock);
- if (stopped)
- goto stop_kupdate;
- }
-#ifdef DEBUG
- printk(KERN_DEBUG "kupdate() activated...\n");
-#endif
- sync_old_buffers();
+ if (!test_and_set_bit(0, &exclude)) {
+ if (pdflush_operation(bdflush, (unsigned long)&exclude))
+ clear_bit(0, &exclude);
}
}

-static int __init bdflush_init(void)
+/*
+ * kupdate
+ */
+static struct timer_list kupdate_timer;
+static void kupdate_handler(unsigned long dummy)
{
- static struct completion startup __initdata = COMPLETION_INITIALIZER(startup);
+ pdflush_operation(sync_old_buffers, 0);
+ mod_timer(&kupdate_timer, jiffies + bdf_prm.b_un.interval);
+}

- kernel_thread(bdflush, &startup, CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
- wait_for_completion(&startup);
- kernel_thread(kupdate, &startup, CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
- wait_for_completion(&startup);
+static int __init kupdate_init(void)
+{
+ init_timer(&kupdate_timer);
+ kupdate_timer.expires = jiffies + bdf_prm.b_un.interval;
+ kupdate_timer.data = 0;
+ kupdate_timer.function = kupdate_handler;
+ add_timer(&kupdate_timer);
return 0;
}

-module_init(bdflush_init)
+module_init(kupdate_init)

-
-
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