/*
 * Copyright 2005-2008, Axel Dörfler, axeld@pinc-software.de.
 * Distributed under the terms of the MIT License.
 */


#include <vm_low_memory.h>

#include <new>
#include <signal.h>
#include <stdlib.h>

#include <KernelExport.h>

#include <elf.h>
#include <lock.h>
#include <sem.h>
#include <util/AutoLock.h>
#include <util/DoublyLinkedList.h>
#include <vm_page.h>
#include <vm_priv.h>


//#define TRACE_LOW_MEMORY
#ifdef TRACE_LOW_MEMORY
#	define TRACE(x)	dprintf x
#else
#	define TRACE(x) ;
#endif


struct low_memory_handler : public DoublyLinkedListLinkImpl<low_memory_handler> {
	low_memory_func	function;
	void			*data;
	int32			priority;
};

typedef DoublyLinkedList<low_memory_handler> HandlerList;


static const bigtime_t kLowMemoryInterval = 3000000;	// 3 secs
static const bigtime_t kWarnMemoryInterval = 500000;	// 0.5 secs

// page limits
static const size_t kNoteLimit = 2048;
static const size_t kWarnLimit = 256;
static const size_t kCriticalLimit = 32;


static int32 sLowMemoryState = B_NO_LOW_MEMORY;
static bigtime_t sLastMeasurement;

static mutex sLowMemoryMutex;
static sem_id sLowMemoryWaitSem;
static HandlerList sLowMemoryHandlers;


static void
call_handlers(int32 level)
{
	MutexLocker locker(&sLowMemoryMutex);
	HandlerList::Iterator iterator = sLowMemoryHandlers.GetIterator();

	while (iterator.HasNext()) {
		low_memory_handler *handler = iterator.Next();

		handler->function(handler->data, level);
	}
}


static int32
compute_state(void)
{
	sLastMeasurement = system_time();

	uint32 freePages = vm_page_num_free_pages();

	if (freePages > kNoteLimit) {
		// TODO: work-around for a missing general low resource handler
		if (sem_used_sems() * 6 > sem_max_sems() * 5)
			return B_LOW_MEMORY_WARNING;
		if (sem_used_sems() * 3 > sem_max_sems() * 2)
			return B_LOW_MEMORY_NOTE;
	}

	if (freePages >= kNoteLimit)
		return B_NO_LOW_MEMORY;

	// specify low memory level
	if (freePages < kCriticalLimit)
		return B_LOW_MEMORY_CRITICAL;
	if (freePages < kWarnLimit)
		return B_LOW_MEMORY_WARNING;

	return B_LOW_MEMORY_NOTE;
}


static int32
low_memory(void *)
{
	bigtime_t timeout = kLowMemoryInterval;
	while (true) {
		if (sLowMemoryState != B_LOW_MEMORY_CRITICAL) {
			acquire_sem_etc(sLowMemoryWaitSem, 1, B_RELATIVE_TIMEOUT,
				timeout);
		}

		sLowMemoryState = compute_state();

		TRACE(("vm_low_memory: state = %ld, %ld free pages\n",
			sLowMemoryState, vm_page_num_free_pages()));

		if (sLowMemoryState < B_LOW_MEMORY_NOTE)
			continue;

		call_handlers(sLowMemoryState);
		
		if (sLowMemoryState == B_LOW_MEMORY_WARNING)
			timeout = kWarnMemoryInterval;
		else
			timeout = kLowMemoryInterval;
	}
	return 0;
}


static int
dump_handlers(int argc, char **argv)
{
	HandlerList::Iterator iterator = sLowMemoryHandlers.GetIterator();
	kprintf("function    data       prio  function-name\n");

	while (iterator.HasNext()) {
		low_memory_handler *handler = iterator.Next();

		const char* symbol = NULL;
		elf_debug_lookup_symbol_address((addr_t)handler->function, NULL,
			&symbol, NULL, NULL);

		kprintf("%p  %p  %3ld  %s\n", handler->function, handler->data,
			handler->priority, symbol);
	}

	return 0;
}


//	#pragma mark - private kernel API


void
vm_low_memory(size_t requirements)
{
	// TODO: take requirements into account

	vm_schedule_page_scanner(requirements);
	release_sem(sLowMemoryWaitSem);
}


int32
vm_low_memory_state(void)
{
	if (system_time() - sLastMeasurement > 500000)
		sLowMemoryState = compute_state();

	return sLowMemoryState;
}


status_t
vm_low_memory_init(void)
{
	new(&sLowMemoryHandlers) HandlerList;
		// static initializers do not work in the kernel,
		// so we have to do it here, manually

	return B_OK;
}


status_t
vm_low_memory_init_post_thread(void)
{
	if (mutex_init(&sLowMemoryMutex, "low memory") < B_OK)
		return B_ERROR;
	
	sLowMemoryWaitSem = create_sem(0, "low memory wait");
	if (sLowMemoryWaitSem < B_OK)
		return sLowMemoryWaitSem;

	thread_id thread = spawn_kernel_thread(&low_memory, "low memory handler",
		B_LOW_PRIORITY, NULL);
	send_signal_etc(thread, SIGCONT, B_DO_NOT_RESCHEDULE);

	add_debugger_command("low_memory", &dump_handlers, "Dump list of low memory handlers");
	return B_OK;
}


status_t
unregister_low_memory_handler(low_memory_func function, void *data)
{
	TRACE(("unregister_low_memory_handler(function = %p, data = %p)\n",
		function, data));

	MutexLocker locker(&sLowMemoryMutex);
	HandlerList::Iterator iterator = sLowMemoryHandlers.GetIterator();

	while (iterator.HasNext()) {
		low_memory_handler *handler = iterator.Next();

		if (handler->function == function && handler->data == data) {
			sLowMemoryHandlers.Remove(handler);
			free(handler);
			return B_OK;
		}
	}

	return B_ENTRY_NOT_FOUND;
}


/*! Registers a low memory handler. The higher the \a priority, the earlier
	the handler will be called in low memory situations.
*/
status_t
register_low_memory_handler(low_memory_func function, void *data,
	int32 priority)
{
	TRACE(("register_low_memory_handler(function = %p, data = %p)\n",
		function, data));

	low_memory_handler *newHandler = (low_memory_handler *)malloc(
		sizeof(low_memory_handler));
	if (newHandler == NULL)
		return B_NO_MEMORY;

	newHandler->function = function;
	newHandler->data = data;
	newHandler->priority = priority;

	MutexLocker locker(&sLowMemoryMutex);

	// sort it in after priority (higher priority comes first)

	HandlerList::ReverseIterator iterator
		= sLowMemoryHandlers.GetReverseIterator();
	low_memory_handler *last = NULL;
	while (iterator.HasNext()) {
		low_memory_handler *handler = iterator.Next();

		if (handler->priority >= priority) {
			sLowMemoryHandlers.Insert(last, newHandler);
			return B_OK;
		}
		last = handler;
	}

	sLowMemoryHandlers.Add(newHandler, false);
	return B_OK;
}