Beginning to add on-demand paging logic

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@2850 42af7a65-404d-4744-a932-0658087f49c3

7 files changed, 472 insertions, 28 deletions

diff --git a/nuttx/include/nuttx/page.h b/nuttx/include/nuttx/page.h
new file mode 100755
index 000000000..33d2daf94
--- /dev/null
+++ b/nuttx/include/nuttx/page.h
@@ -0,0 +1,150 @@
+/****************************************************************************
+ * include/nuttx/page.h
+ * This file defines interfaces used to support NuttX On-Demand Paging.
+ *
+ *   Copyright (C) 2010 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#ifndef __NUTTX_PAGE_H
+#define __NUTTX_PAGE_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <nuttx/wqueue.h>
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Pre-Processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+#ifndef __ASSEMBLY
+ 
+#undef EXTERN
+#if defined(__cplusplus)
+#define EXTERN extern "C"
+extern "C" {
+#else
+#define EXTERN extern
+#endif
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pg_miss
+ *
+ * Description:
+ *   This function is called from architecture-specific memory segmentaion
+ *   fault handling logic.  This function will perform the following
+ *   operations:
+ *
+ *   1) Sanity checking.
+ *      - ASSERT if the currently executing task is the page fill worker
+ *        thread.  The page fill worker thread is how the the page fault
+ *        is resolved and all logic associated with the page fill worker
+ *        must be "locked" and always present in memory.
+ *   2) Block the currently executing task.
+ *      - Call up_block_task() to block the task at the head of the ready-
+ *        to-run list.  This should cause an interrupt level context switch
+ *        to the next highest priority task.
+ *      - The blocked task will be marked with state TSTATE_WAIT_PAGEFILL
+ *        and will be retained in the g_waitingforfill prioritized task
+ *        list.
+ *   3) Boost the page fill worker thread priority.
+ *      - Check the priority of the task at the head of the g_waitingforfill
+ *        list.  If the priority of that task is higher than the current
+ *        priority of the page fill worker thread, then boost the priority
+ *        of the page fill worker thread to that priority.
+ *   4) Signal the page fill worker thread.
+ *      - Is there a page fill pending?  If not then signal the worker
+ *        thread to start working on the queued page fill requests.
+ *
+ * Input Parameters:
+ *   None - The head of the ready-to-run list is assumed to be task that
+ *   caused the exception.
+ *
+ * Returned Value:
+ *   None - Either this function function succeeds or an assertion occurs.
+ *
+ * Assumptions:
+ *   - It is assumed that this function is called from the level of an
+ *     exception handler and that all interrupts are disabled.
+ *   - It is assumed that currently executing task (the one at the head of
+ *     the ready-to-run list) is the one that cause the fault.  This will
+ *     always be true unless the page fault occurred in an interrupt handler.
+ *     Interrupt handling logic must always be present and "locked" into
+ *     memory.
+ *   - The chip-specific page fault exception handler has already verified
+ *     that the exception did not occur from interrupt/exception handling
+ *     logic.
+ *   - As mentioned above, the task causing the page fault must not be the
+ *     the page fill worker thread because that is the only way to complete
+ *     the page fill.
+ *
+ * NOTES:
+ *   1. One way to accomplish this would be a two pass link phase:
+ *      - In the first phase, create a partially linked objected containing
+ *        all interrupt/exception handling logic, the page fill worker thread
+ *        plus all parts of the IDLE thread (which must always be available
+ *        for execution).
+ *      - All of the .text and .rodata sections of this partial link should
+ *        be collected into a single section.
+ *      - The second link would link the partially linked object along with
+ *        the remaining object to produce the final binary.  The linker
+ *        script should position the "special" section so that it lies
+ *        in a reserved, "non-swappable" region.
+ *
+ ****************************************************************************/
+
+EXTERN void pg_miss(void);
+
+#undef EXTERN
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* __ASSEMBLY */
+#endif /* CONFIG_PAGING */
+#endif /* __NUTTX_PAGE_H */
diff --git a/nuttx/include/nuttx/sched.h b/nuttx/include/nuttx/sched.h
index 2667999d8..169072174 100644
--- a/nuttx/include/nuttx/sched.h
+++ b/nuttx/include/nuttx/sched.h
@@ -1,7 +1,7 @@
 /********************************************************************************
  * nuttx/sched.h
  *
- *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2010 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -87,21 +87,23 @@
 enum tstate_e
 {
   TSTATE_TASK_INVALID    = 0, /* INVALID      - The TCB is uninitialized */
-  TSTATE_TASK_PENDING    = 1, /* READY_TO_RUN - Pending preemption unlock */
-  TSTATE_TASK_READYTORUN = 2, /* READY-TO-RUN - But not running */
-  TSTATE_TASK_RUNNING    = 3, /* READY_TO_RUN - And running */
+  TSTATE_TASK_PENDING,        /* READY_TO_RUN - Pending preemption unlock */
+  TSTATE_TASK_READYTORUN,     /* READY-TO-RUN - But not running */
+  TSTATE_TASK_RUNNING,        /* READY_TO_RUN - And running */
 
-  TSTATE_TASK_INACTIVE   = 4, /* BLOCKED      - Initialized but not yet activated */
-  TSTATE_WAIT_SEM        = 5  /* BLOCKED      - Waiting for a semaphore */
+  TSTATE_TASK_INACTIVE,       /* BLOCKED      - Initialized but not yet activated */
+  TSTATE_WAIT_SEM,            /* BLOCKED      - Waiting for a semaphore */
 #ifndef CONFIG_DISABLE_SIGNALS
-  ,
-  TSTATE_WAIT_SIG        = 6  /* BLOCKED      - Waiting for a signal */
+  TSTATE_WAIT_SIG,            /* BLOCKED      - Waiting for a signal */
 #endif
 #ifndef CONFIG_DISABLE_MQUEUE
-  ,
   TSTATE_WAIT_MQNOTEMPTY,     /* BLOCKED      - Waiting for a MQ to become not empty. */
-  TSTATE_WAIT_MQNOTFULL       /* BLOCKED      - Waiting for a MQ to become not full. */
+  TSTATE_WAIT_MQNOTFULL.      /* BLOCKED      - Waiting for a MQ to become not full. */
 #endif
+#ifdef CONFIG_PAGING
+  TSTATE_WAIT_PAGEFILL,       /* BLOCKED     - Waiting for page fill */
+#endif
+  NUM_TASK_STATES             /* Must be last */
 };
 typedef enum tstate_e tstate_t;
 
@@ -110,22 +112,7 @@ typedef enum tstate_e tstate_t;
 #define FIRST_READY_TO_RUN_STATE TSTATE_TASK_READYTORUN
 #define LAST_READY_TO_RUN_STATE  TSTATE_TASK_RUNNING
 #define FIRST_BLOCKED_STATE      TSTATE_TASK_INACTIVE
-#ifndef CONFIG_DISABLE_MQUEUE
-# define LAST_BLOCKED_STATE      TSTATE_WAIT_MQNOTFULL
-# ifndef CONFIG_DISABLE_SIGNALS
-#  define NUM_TASK_STATES        9
-# else
-#  define NUM_TASK_STATES        8
-# endif
-#else
-# ifndef CONFIG_DISABLE_SIGNALS
-#  define LAST_BLOCKED_STATE     TSTATE_WAIT_SIG
-#  define NUM_TASK_STATES        7
-# else
-#  define LAST_BLOCKED_STATE     TSTATE_WAIT_SEM
-#  define NUM_TASK_STATES        6
-# endif
-#endif
+#define LAST_BLOCKED_STATE       (NUM_TASK_STATES-1)
 
 /* The following is the form of a thread start-up function */
 
diff --git a/nuttx/include/signal.h b/nuttx/include/signal.h
index 40fb3cbf0..59bf891e8 100644
--- a/nuttx/include/signal.h
+++ b/nuttx/include/signal.h
@@ -96,7 +96,9 @@
 #endif
 #endif
 
-#ifdef CONFIG_SCHED_WORKQUEUE
+/* SIGWORK is used to wake up various internal, NuttX worker thread */
+
+#if defined(CONFIG_SCHED_WORKQUEUE) || defined(CONFIG_PAGING)
 #ifndef CONFIG_SIG_SIGWORK
 #define SIGWORK         4  /* Used to wake up the work queue */
 #else
diff --git a/nuttx/sched/Makefile b/nuttx/sched/Makefile
index ec9923e1c..40392504c 100644
--- a/nuttx/sched/Makefile
+++ b/nuttx/sched/Makefile
@@ -139,10 +139,15 @@ ifeq ($(CONFIG_SCHED_WORKQUEUE),y)
 WORK_SRCS	= work_thread.c work_queue.c work_cancel.c
 endif
 
+ifeq ($(CONFIG_PAGING),y)
+PGFILL_SRCS	= pg_miss.c
+endif
+
 IRQ_SRCS	= irq_initialize.c irq_attach.c irq_dispatch.c irq_unexpectedisr.c
 
 CSRCS		= $(MISC_SRCS) $(TSK_SRCS) $(SCHED_SRCS) $(WDOG_SRCS) $(TIME_SRCS) \
-		  $(SEM_SRCS) $(TIMER_SRCS) $(WORK_SRCS) $(IRQ_SRCS)
+		  $(SEM_SRCS) $(TIMER_SRCS) $(WORK_SRCS) $(PGFILL_SRCS) $(IRQ_SRCS)
+
 ifneq ($(CONFIG_DISABLE_CLOCK),y)
 CSRCS		+= $(CLOCK_SRCS)
 endif
diff --git a/nuttx/sched/os_start.c b/nuttx/sched/os_start.c
index 78b1c7997..ac52c4d66 100644
--- a/nuttx/sched/os_start.c
+++ b/nuttx/sched/os_start.c
@@ -130,6 +130,12 @@ volatile dq_queue_t g_waitingformqnotempty;
 volatile dq_queue_t g_waitingformqnotfull;
 #endif
 
+/* This is the list of all tasks that are blocking waiting for a page fill */
+
+#ifdef CONFIG_PAGING
+volatile dq_queue_t g_waitingforfill;
+#endif
+
 /* This the list of all tasks that have been initialized, but not yet
  * activated. NOTE:  This is the only list that is not prioritized.
  */
@@ -166,6 +172,12 @@ pidhash_t g_pidhash[CONFIG_MAX_TASKS];
 pid_t g_worker;
 #endif
 
+/* The task ID of the page fill worker thread */
+
+#ifdef CONFIG_PAGING
+pid_t g_pgworker;
+#endif
+
 /* This is a table of task lists.  This table is indexed by
  * the task state enumeration type (tstate_t) and provides
  * a pointer to the associated static task list (if there
@@ -188,6 +200,9 @@ const tasklist_t g_tasklisttable[NUM_TASK_STATES] =
   { &g_waitingformqnotempty, true  },  /* TSTATE_WAIT_MQNOTEMPTY */
   { &g_waitingformqnotfull,  true  }   /* TSTATE_WAIT_MQNOTFULL */
 #endif
+#ifdef CONFIG_PAGING
+  { &g_waitingforfill,       true  }   /* TSTATE_WAIT_PAGEFILL */
+#endif
 };
 
 /****************************************************************************
@@ -240,6 +255,9 @@ void os_start(void)
   dq_init(&g_waitingformqnotfull);
   dq_init(&g_waitingformqnotempty);
 #endif
+#ifdef CONFIG_PAGING
+  dq_init(&g_waitingforfill);
+#endif
   dq_init(&g_inactivetasks);
   sq_init(&g_delayeddeallocations);
 
diff --git a/nuttx/sched/pg_internal.h b/nuttx/sched/pg_internal.h
new file mode 100755
index 000000000..5a22daad1
--- /dev/null
+++ b/nuttx/sched/pg_internal.h
@@ -0,0 +1,107 @@
+/****************************************************************************
+ * sched/pg_internal.h
+ *
+ *   Copyright (C) 2010 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#ifndef __SCHED_PG_INTERNAL_H
+#define __SCHED_PG_INTERNAL_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+ 
+#include <nuttx/config.h>
+#include <queue.h>
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Pre-Processor Definitions
+ ****************************************************************************/
+
+/* Configuration ************************************************************/
+
+#ifndef CONFIG_PAGING_WORKPRIORITY
+#  define CONFIG_PAGING_WORKPRIORITY 50
+#endif
+
+#ifndef CONFIG_PAGING_WORKSTACKSIZE
+#  define CONFIG_PAGING_WORKSTACKSIZE CONFIG_IDLETHREAD_STACKSIZE
+#endif
+
+#ifdef CONFIG_DISABLE_SIGNALS
+#  warning "Page fill support requires signals"
+#endif
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+#ifndef __ASSEMBLY
+
+/* If is the PID of the page fill worker thread */
+
+extern pid_t g_pgworker;
+
+/* If non-NULL, this points to the TCB of the task currently being filled */
+
+extern FAR _TCB *g_filltcb;
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pg_worker
+ *
+ * Description:
+ *   This is the entry point of the worker thread that performs the actual
+ *   page file.
+ *
+ * Input parameters:
+ *   argc, argv (not used)
+ *
+ * Returned Value:
+ *   Does not return
+ *
+ ****************************************************************************/
+
+extern int pg_worker(int argc, char *argv[]);
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_PAGING */
+#endif /* __SCHED_PG_INTERNAL_H */
diff --git a/nuttx/sched/pg_miss.c b/nuttx/sched/pg_miss.c
new file mode 100644
index 000000000..54170f8c5
--- /dev/null
+++ b/nuttx/sched/pg_miss.c
@@ -0,0 +1,175 @@
+/****************************************************************************
+ * sched/pg_miss.c
+ *
+ *   Copyright (C) 2010 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <debug.h>
+#include <errno.h>
+
+#include <nuttx/arch.h>
+#include <nuttx/sched.h>
+#include <nuttx/page.h>
+
+#ifdef CONFIG_PAGING
+
+#include "os_internal.h"
+#include "pg_internal.h"
+
+/****************************************************************************
+ * Global Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pg_miss
+ *
+ * Description:
+ *   This function is called from architecture-specific memory segmentaion
+ *   fault handling logic.  This function will perform the following
+ *   operations:
+ *
+ *   1) Sanity checking.
+ *      - ASSERT if the currently executing task is the page fill worker
+ *        thread.  The page fill worker thread is how the the page fault
+ *        is resolved and all logic associated with the page fill worker
+ *        must be "locked" and always present in memory.
+ *      - ASSERT if an interrupt was executing at the time of the exception.
+ *   2) Block the currently executing task.
+ *      - Call up_block_task() to block the task at the head of the ready-
+ *        to-run list.  This should cause an interrupt level context switch
+ *        to the next highest priority task.
+ *      - The blocked task will be marked with state TSTATE_WAIT_PAGEFILL
+ *        and will be retained in the g_waitingforfill prioritized task
+ *        list.
+ *   3) Boost the page fill worker thread priority.
+ *      - Check the priority of the task at the head of the g_waitingforfill
+ *        list.  If the priority of that task is higher than the current
+ *        priority of the page fill worker thread, then boost the priority
+ *        of the page fill worker thread to that priority.
+ *   4) Signal the page fill worker thread.
+ *      - Is there a page fill pending?  If not then signal the worker
+ *        thread to start working on the queued page fill requests.
+ *
+ * Input Parameters:
+ *   None - The head of the ready-to-run list is assumed to be task that
+ *   caused the exception.
+ *
+ * Returned Value:
+ *   None - Either this function function succeeds or an assertion occurs.
+ *
+ * Assumptions:
+ *   - It is assumed that this function is called from the level of an
+ *     exception handler and that all interrupts are disabled.
+ *   - It is assumed that currently executing task (the one at the head of
+ *     the ready-to-run list) is the one that cause the fault.  This will
+ *     always be true unless the page fault occurred in an interrupt handler.
+ *     Interrupt handling logic must always be present and "locked" into
+ *     memory.
+ *   - As mentioned above, the task causing the page fault must not be the
+ *     the page fill worker thread because that is the only way to complete
+ *     the page fill.
+ *
+ * NOTES:
+ *   1. One way to accomplish this would be a two pass link phase:
+ *      - In the first phase, create a partially linked objected containing
+ *        all interrupt/exception handling logic, the page fill worker thread
+ *        plus all parts of the IDLE thread (which must always be available
+ *        for execution).
+ *      - All of the .text and .rodata sections of this partial link should
+ *        be collected into a single section.
+ *      - The second link would link the partially linked object along with
+ *        the remaining object to produce the final binary.  The linker
+ *        script should position the "special" section so that it lies
+ *        in a reserved, "non-swappable" region.
+ *
+ ****************************************************************************/
+
+void pg_miss(void)
+{
+  FAR _TCB *ftcb = (FAR _TCB*)g_readytorun.head;
+  FAR _TCB *wtcb;
+
+  /* Sanity checking
+   *
+   * ASSERT if the currently executing task is the page fill worker thread.
+   * The page fill worker thread is how the the page fault is resolved and
+   * all logic associated with the page fill worker must be "locked" and
+   * always present in memory.
+   */
+
+  DEBUGASSERT(g_pgworker != ftcb->pid);
+
+  /* Block the currently executing task
+   * - Call up_block_task() to block the task at the head of the ready-
+   *   to-run list.  This should cause an interrupt level context switch
+   *   to the next highest priority task.
+   * - The blocked task will be marked with state TSTATE_WAIT_PAGEFILL
+   *   and will be retained in the g_waitingforfill prioritized task list.
+   */
+
+  up_block_task(ftcb, TSTATE_WAIT_PAGEFILL);
+
+  /* Boost the page fill worker thread priority.
+   * - Check the priority of the task at the head of the g_waitingforfill
+   *   list.  If the priority of that task is higher than the current
+   *   priority of the page fill worker thread, then boost the priority
+   *   of the page fill worker thread to that priority.
+   */
+
+  wtcb = sched_gettcb(g_pgworker);
+  DEBUGASSERT(wtcb != NULL);
+
+  if (wtcb->sched_priority < ftcb->sched_priority)
+    {
+      /* Reprioritize the page fill worker thread */
+
+      sched_setpriority(wtcb, ftcb->sched_priority);
+    }
+
+  /* Signal the page fill worker thread.
+   * - Is there a page fill pending?  If not then signal the worker
+   *   thread to start working on the queued page fill requests.
+   */
+
+  if (!g_filltcb)
+    {
+      kill(g_pgworker, SIGWORK);
+    }
+}
+
+#endif /* CONFIG_PAGING */