mm/highmem.c - kernel/msm - Gitiles

 /*
  * High memory handling common code and variables.
  *
  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
  *
  *
  * Redesigned the x86 32-bit VM architecture to deal with
  * 64-bit physical space. With current x86 CPUs this
  * means up to 64 Gigabytes physical RAM.
  *
  * Rewrote high memory support to move the page cache into
  * high memory. Implemented permanent (schedulable) kmaps
  * based on Linus' idea.
  *
  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  */

 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/swap.h>
 #include <linux/bio.h>
 #include <linux/pagemap.h>
 #include <linux/mempool.h>
 #include <linux/blkdev.h>
 #include <linux/init.h>
 #include <linux/hash.h>
 #include <linux/highmem.h>
 #include <asm/tlbflush.h>

 static mempool_t *page_pool, *isa_page_pool;

 static void *page_pool_alloc(unsigned int __nocast gfp_mask, void *data)
 {
 	unsigned int gfp = gfp_mask | (unsigned int) (long) data;

 	return alloc_page(gfp);
 }

 static void page_pool_free(void *page, void *data)
 {
 	__free_page(page);
 }

 /*
  * Virtual_count is not a pure "count".
  *  0 means that it is not mapped, and has not been mapped
  *    since a TLB flush - it is usable.
  *  1 means that there are no users, but it has been mapped
  *    since the last TLB flush - so we can't use it.
  *  n means that there are (n-1) current users of it.
  */
 #ifdef CONFIG_HIGHMEM
 static int pkmap_count[LAST_PKMAP];
 static unsigned int last_pkmap_nr;
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);

 pte_t * pkmap_page_table;

 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);

 static void flush_all_zero_pkmaps(void)
 {
 	int i;

 	flush_cache_kmaps();

 	for (i = 0; i < LAST_PKMAP; i++) {
 		struct page *page;

 		/*
 		 * zero means we don't have anything to do,
 		 * >1 means that it is still in use. Only
 		 * a count of 1 means that it is free but
 		 * needs to be unmapped
 		 */
 		if (pkmap_count[i] != 1)
 			continue;
 		pkmap_count[i] = 0;

 		/* sanity check */
 		if (pte_none(pkmap_page_table[i]))
 			BUG();

 		/*
 		 * Don't need an atomic fetch-and-clear op here;
 		 * no-one has the page mapped, and cannot get at
 		 * its virtual address (and hence PTE) without first
 		 * getting the kmap_lock (which is held here).
 		 * So no dangers, even with speculative execution.
 		 */
 		page = pte_page(pkmap_page_table[i]);
 		pte_clear(&init_mm, (unsigned long)page_address(page),
 			  &pkmap_page_table[i]);

 		set_page_address(page, NULL);
 	}
 	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 }

 static inline unsigned long map_new_virtual(struct page *page)
 {
 	unsigned long vaddr;
 	int count;

 start:
 	count = LAST_PKMAP;
 	/* Find an empty entry */
 	for (;;) {
 		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
 		if (!last_pkmap_nr) {
 			flush_all_zero_pkmaps();
 			count = LAST_PKMAP;
 		}
 		if (!pkmap_count[last_pkmap_nr])
 			break;	/* Found a usable entry */
 		if (--count)
 			continue;

 		/*
 		 * Sleep for somebody else to unmap their entries
 		 */
 		{
 			DECLARE_WAITQUEUE(wait, current);

 			__set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&pkmap_map_wait, &wait);
 			spin_unlock(&kmap_lock);
 			schedule();
 			remove_wait_queue(&pkmap_map_wait, &wait);
 			spin_lock(&kmap_lock);

 			/* Somebody else might have mapped it while we slept */
 			if (page_address(page))
 				return (unsigned long)page_address(page);

 			/* Re-start */
 			goto start;
 		}
 	}
 	vaddr = PKMAP_ADDR(last_pkmap_nr);
 	set_pte_at(&init_mm, vaddr,
 		   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

 	pkmap_count[last_pkmap_nr] = 1;
 	set_page_address(page, (void *)vaddr);

 	return vaddr;
 }

 void fastcall *kmap_high(struct page *page)
 {
 	unsigned long vaddr;

 	/*
 	 * For highmem pages, we can't trust "virtual" until
 	 * after we have the lock.
 	 *
 	 * We cannot call this from interrupts, as it may block
 	 */
 	spin_lock(&kmap_lock);
 	vaddr = (unsigned long)page_address(page);
 	if (!vaddr)
 		vaddr = map_new_virtual(page);
 	pkmap_count[PKMAP_NR(vaddr)]++;
 	if (pkmap_count[PKMAP_NR(vaddr)] < 2)
 		BUG();
 	spin_unlock(&kmap_lock);
 	return (void*) vaddr;
 }

 EXPORT_SYMBOL(kmap_high);

 void fastcall kunmap_high(struct page *page)
 {
 	unsigned long vaddr;
 	unsigned long nr;
 	int need_wakeup;

 	spin_lock(&kmap_lock);
 	vaddr = (unsigned long)page_address(page);
 	if (!vaddr)
 		BUG();
 	nr = PKMAP_NR(vaddr);

 	/*
 	 * A count must never go down to zero
 	 * without a TLB flush!
 	 */
 	need_wakeup = 0;
 	switch (--pkmap_count[nr]) {
 	case 0:
 		BUG();
 	case 1:
 		/*
 		 * Avoid an unnecessary wake_up() function call.
 		 * The common case is pkmap_count[] == 1, but
 		 * no waiters.
 		 * The tasks queued in the wait-queue are guarded
 		 * by both the lock in the wait-queue-head and by
 		 * the kmap_lock.  As the kmap_lock is held here,
 		 * no need for the wait-queue-head's lock.  Simply
 		 * test if the queue is empty.
 		 */
 		need_wakeup = waitqueue_active(&pkmap_map_wait);
 	}
 	spin_unlock(&kmap_lock);

 	/* do wake-up, if needed, race-free outside of the spin lock */
 	if (need_wakeup)
 		wake_up(&pkmap_map_wait);
 }

 EXPORT_SYMBOL(kunmap_high);

 #define POOL_SIZE	64

 static __init int init_emergency_pool(void)
 {
 	struct sysinfo i;
 	si_meminfo(&i);
 	si_swapinfo(&i);

 	if (!i.totalhigh)
 		return 0;

 	page_pool = mempool_create(POOL_SIZE, page_pool_alloc, page_pool_free, NULL);
 	if (!page_pool)
 		BUG();
 	printk("highmem bounce pool size: %d pages\n", POOL_SIZE);

 	return 0;
 }

 __initcall(init_emergency_pool);

 /*
  * highmem version, map in to vec
  */
 static void bounce_copy_vec(struct bio_vec *to, unsigned char *vfrom)
 {
 	unsigned long flags;
 	unsigned char *vto;

 	local_irq_save(flags);
 	vto = kmap_atomic(to->bv_page, KM_BOUNCE_READ);
 	memcpy(vto + to->bv_offset, vfrom, to->bv_len);
 	kunmap_atomic(vto, KM_BOUNCE_READ);
 	local_irq_restore(flags);
 }

 #else /* CONFIG_HIGHMEM */

 #define bounce_copy_vec(to, vfrom)	\
 	memcpy(page_address((to)->bv_page) + (to)->bv_offset, vfrom, (to)->bv_len)

 #endif

 #define ISA_POOL_SIZE	16

 /*
  * gets called "every" time someone init's a queue with BLK_BOUNCE_ISA
  * as the max address, so check if the pool has already been created.
  */
 int init_emergency_isa_pool(void)
 {
 	if (isa_page_pool)
 		return 0;

 	isa_page_pool = mempool_create(ISA_POOL_SIZE, page_pool_alloc, page_pool_free, (void *) __GFP_DMA);
 	if (!isa_page_pool)
 		BUG();

 	printk("isa bounce pool size: %d pages\n", ISA_POOL_SIZE);
 	return 0;
 }

 /*
  * Simple bounce buffer support for highmem pages. Depending on the
  * queue gfp mask set, *to may or may not be a highmem page. kmap it
  * always, it will do the Right Thing
  */
 static void copy_to_high_bio_irq(struct bio *to, struct bio *from)
 {
 	unsigned char *vfrom;
 	struct bio_vec *tovec, *fromvec;
 	int i;

 	__bio_for_each_segment(tovec, to, i, 0) {
 		fromvec = from->bi_io_vec + i;

 		/*
 		 * not bounced
 		 */
 		if (tovec->bv_page == fromvec->bv_page)
 			continue;

 		/*
 		 * fromvec->bv_offset and fromvec->bv_len might have been
 		 * modified by the block layer, so use the original copy,
 		 * bounce_copy_vec already uses tovec->bv_len
 		 */
 		vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;

 		flush_dcache_page(tovec->bv_page);
 		bounce_copy_vec(tovec, vfrom);
 	}
 }

 static void bounce_end_io(struct bio *bio, mempool_t *pool, int err)
 {
 	struct bio *bio_orig = bio->bi_private;
 	struct bio_vec *bvec, *org_vec;
 	int i;

 	if (test_bit(BIO_EOPNOTSUPP, &bio->bi_flags))
 		set_bit(BIO_EOPNOTSUPP, &bio_orig->bi_flags);

 	/*
 	 * free up bounce indirect pages used
 	 */
 	__bio_for_each_segment(bvec, bio, i, 0) {
 		org_vec = bio_orig->bi_io_vec + i;
 		if (bvec->bv_page == org_vec->bv_page)
 			continue;

 		mempool_free(bvec->bv_page, pool);
 		dec_page_state(nr_bounce);
 	}

 	bio_endio(bio_orig, bio_orig->bi_size, err);
 	bio_put(bio);
 }

 static int bounce_end_io_write(struct bio *bio, unsigned int bytes_done,int err)
 {
 	if (bio->bi_size)
 		return 1;

 	bounce_end_io(bio, page_pool, err);
 	return 0;
 }

 static int bounce_end_io_write_isa(struct bio *bio, unsigned int bytes_done, int err)
 {
 	if (bio->bi_size)
 		return 1;

 	bounce_end_io(bio, isa_page_pool, err);
 	return 0;
 }

 static void __bounce_end_io_read(struct bio *bio, mempool_t *pool, int err)
 {
 	struct bio *bio_orig = bio->bi_private;

 	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
 		copy_to_high_bio_irq(bio_orig, bio);

 	bounce_end_io(bio, pool, err);
 }

 static int bounce_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
 {
 	if (bio->bi_size)
 		return 1;

 	__bounce_end_io_read(bio, page_pool, err);
 	return 0;
 }

 static int bounce_end_io_read_isa(struct bio *bio, unsigned int bytes_done, int err)
 {
 	if (bio->bi_size)
 		return 1;

 	__bounce_end_io_read(bio, isa_page_pool, err);
 	return 0;
 }

 static void __blk_queue_bounce(request_queue_t *q, struct bio **bio_orig,
 			mempool_t *pool)
 {
 	struct page *page;
 	struct bio *bio = NULL;
 	int i, rw = bio_data_dir(*bio_orig);
 	struct bio_vec *to, *from;

 	bio_for_each_segment(from, *bio_orig, i) {
 		page = from->bv_page;

 		/*
 		 * is destination page below bounce pfn?
 		 */
 		if (page_to_pfn(page) < q->bounce_pfn)
 			continue;

 		/*
 		 * irk, bounce it
 		 */
 		if (!bio)
 			bio = bio_alloc(GFP_NOIO, (*bio_orig)->bi_vcnt);

 		to = bio->bi_io_vec + i;

 		to->bv_page = mempool_alloc(pool, q->bounce_gfp);
 		to->bv_len = from->bv_len;
 		to->bv_offset = from->bv_offset;
 		inc_page_state(nr_bounce);

 		if (rw == WRITE) {
 			char *vto, *vfrom;

 			flush_dcache_page(from->bv_page);
 			vto = page_address(to->bv_page) + to->bv_offset;
 			vfrom = kmap(from->bv_page) + from->bv_offset;
 			memcpy(vto, vfrom, to->bv_len);
 			kunmap(from->bv_page);
 		}
 	}

 	/*
 	 * no pages bounced
 	 */
 	if (!bio)
 		return;

 	/*
 	 * at least one page was bounced, fill in possible non-highmem
 	 * pages
 	 */
 	__bio_for_each_segment(from, *bio_orig, i, 0) {
 		to = bio_iovec_idx(bio, i);
 		if (!to->bv_page) {
 			to->bv_page = from->bv_page;
 			to->bv_len = from->bv_len;
 			to->bv_offset = from->bv_offset;
 		}
 	}

 	bio->bi_bdev = (*bio_orig)->bi_bdev;
 	bio->bi_flags |= (1 << BIO_BOUNCED);
 	bio->bi_sector = (*bio_orig)->bi_sector;
 	bio->bi_rw = (*bio_orig)->bi_rw;

 	bio->bi_vcnt = (*bio_orig)->bi_vcnt;
 	bio->bi_idx = (*bio_orig)->bi_idx;
 	bio->bi_size = (*bio_orig)->bi_size;

 	if (pool == page_pool) {
 		bio->bi_end_io = bounce_end_io_write;
 		if (rw == READ)
 			bio->bi_end_io = bounce_end_io_read;
 	} else {
 		bio->bi_end_io = bounce_end_io_write_isa;
 		if (rw == READ)
 			bio->bi_end_io = bounce_end_io_read_isa;
 	}

 	bio->bi_private = *bio_orig;
 	*bio_orig = bio;
 }

 void blk_queue_bounce(request_queue_t *q, struct bio **bio_orig)
 {
 	mempool_t *pool;

 	/*
 	 * for non-isa bounce case, just check if the bounce pfn is equal
 	 * to or bigger than the highest pfn in the system -- in that case,
 	 * don't waste time iterating over bio segments
 	 */
 	if (!(q->bounce_gfp & GFP_DMA)) {
 		if (q->bounce_pfn >= blk_max_pfn)
 			return;
 		pool = page_pool;
 	} else {
 		BUG_ON(!isa_page_pool);
 		pool = isa_page_pool;
 	}

 	/*
 	 * slow path
 	 */
 	__blk_queue_bounce(q, bio_orig, pool);
 }

 EXPORT_SYMBOL(blk_queue_bounce);

 #if defined(HASHED_PAGE_VIRTUAL)

 #define PA_HASH_ORDER	7

 /*
  * Describes one page->virtual association
  */
 struct page_address_map {
 	struct page *page;
 	void *virtual;
 	struct list_head list;
 };

 /*
  * page_address_map freelist, allocated from page_address_maps.
  */
 static struct list_head page_address_pool;	/* freelist */
 static spinlock_t pool_lock;			/* protects page_address_pool */

 /*
  * Hash table bucket
  */
 static struct page_address_slot {
 	struct list_head lh;			/* List of page_address_maps */
 	spinlock_t lock;			/* Protect this bucket's list */
 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];

 static struct page_address_slot *page_slot(struct page *page)
 {
 	return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 }

 void *page_address(struct page *page)
 {
 	unsigned long flags;
 	void *ret;
 	struct page_address_slot *pas;

 	if (!PageHighMem(page))
 		return lowmem_page_address(page);

 	pas = page_slot(page);
 	ret = NULL;
 	spin_lock_irqsave(&pas->lock, flags);
 	if (!list_empty(&pas->lh)) {
 		struct page_address_map *pam;

 		list_for_each_entry(pam, &pas->lh, list) {
 			if (pam->page == page) {
 				ret = pam->virtual;
 				goto done;
 			}
 		}
 	}
 done:
 	spin_unlock_irqrestore(&pas->lock, flags);
 	return ret;
 }

 EXPORT_SYMBOL(page_address);

 void set_page_address(struct page *page, void *virtual)
 {
 	unsigned long flags;
 	struct page_address_slot *pas;
 	struct page_address_map *pam;

 	BUG_ON(!PageHighMem(page));

 	pas = page_slot(page);
 	if (virtual) {		/* Add */
 		BUG_ON(list_empty(&page_address_pool));

 		spin_lock_irqsave(&pool_lock, flags);
 		pam = list_entry(page_address_pool.next,
 				struct page_address_map, list);
 		list_del(&pam->list);
 		spin_unlock_irqrestore(&pool_lock, flags);

 		pam->page = page;
 		pam->virtual = virtual;

 		spin_lock_irqsave(&pas->lock, flags);
 		list_add_tail(&pam->list, &pas->lh);
 		spin_unlock_irqrestore(&pas->lock, flags);
 	} else {		/* Remove */
 		spin_lock_irqsave(&pas->lock, flags);
 		list_for_each_entry(pam, &pas->lh, list) {
 			if (pam->page == page) {
 				list_del(&pam->list);
 				spin_unlock_irqrestore(&pas->lock, flags);
 				spin_lock_irqsave(&pool_lock, flags);
 				list_add_tail(&pam->list, &page_address_pool);
 				spin_unlock_irqrestore(&pool_lock, flags);
 				goto done;
 			}
 		}
 		spin_unlock_irqrestore(&pas->lock, flags);
 	}
 done:
 	return;
 }

 static struct page_address_map page_address_maps[LAST_PKMAP];

 void __init page_address_init(void)
 {
 	int i;

 	INIT_LIST_HEAD(&page_address_pool);
 	for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
 		list_add(&page_address_maps[i].list, &page_address_pool);
 	for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 		INIT_LIST_HEAD(&page_address_htable[i].lh);
 		spin_lock_init(&page_address_htable[i].lock);
 	}
 	spin_lock_init(&pool_lock);
 }

 #endif	/* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
	/*
	* High memory handling common code and variables.
	*
	* (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
	* Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
	*
	*
	* Redesigned the x86 32-bit VM architecture to deal with
	* 64-bit physical space. With current x86 CPUs this
	* means up to 64 Gigabytes physical RAM.
	*
	* Rewrote high memory support to move the page cache into
	* high memory. Implemented permanent (schedulable) kmaps
	* based on Linus' idea.
	*
	* Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
	*/

	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/swap.h>
	#include <linux/bio.h>
	#include <linux/pagemap.h>
	#include <linux/mempool.h>
	#include <linux/blkdev.h>
	#include <linux/init.h>
	#include <linux/hash.h>
	#include <linux/highmem.h>
	#include <asm/tlbflush.h>

	static mempool_t page_pool, isa_page_pool;

	static void page_pool_alloc(unsigned int __nocast gfp_mask, void data)
	{
	unsigned int gfp = gfp_mask \| (unsigned int) (long) data;

	return alloc_page(gfp);
	}

	static void page_pool_free(void page, void data)
	{
	__free_page(page);
	}

	/*
	* Virtual_count is not a pure "count".
	* 0 means that it is not mapped, and has not been mapped
	* since a TLB flush - it is usable.
	* 1 means that there are no users, but it has been mapped
	* since the last TLB flush - so we can't use it.
	* n means that there are (n-1) current users of it.
	*/
	#ifdef CONFIG_HIGHMEM
	static int pkmap_count[LAST_PKMAP];
	static unsigned int last_pkmap_nr;
	static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);

	pte_t * pkmap_page_table;

	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);

	static void flush_all_zero_pkmaps(void)
	{
	int i;

	flush_cache_kmaps();

	for (i = 0; i < LAST_PKMAP; i++) {
	struct page *page;

	/*
	* zero means we don't have anything to do,
	* >1 means that it is still in use. Only
	* a count of 1 means that it is free but
	* needs to be unmapped
	*/
	if (pkmap_count[i] != 1)
	continue;
	pkmap_count[i] = 0;

	/* sanity check */
	if (pte_none(pkmap_page_table[i]))
	BUG();

	/*
	* Don't need an atomic fetch-and-clear op here;
	* no-one has the page mapped, and cannot get at
	* its virtual address (and hence PTE) without first
	* getting the kmap_lock (which is held here).
	* So no dangers, even with speculative execution.
	*/
	page = pte_page(pkmap_page_table[i]);
	pte_clear(&init_mm, (unsigned long)page_address(page),
	&pkmap_page_table[i]);

	set_page_address(page, NULL);
	}
	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
	}

	static inline unsigned long map_new_virtual(struct page *page)
	{
	unsigned long vaddr;
	int count;

	start:
	count = LAST_PKMAP;
	/* Find an empty entry */
	for (;;) {
	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
	if (!last_pkmap_nr) {
	flush_all_zero_pkmaps();
	count = LAST_PKMAP;
	}
	if (!pkmap_count[last_pkmap_nr])
	break; /* Found a usable entry */
	if (--count)
	continue;

	/*
	* Sleep for somebody else to unmap their entries
	*/
	{
	DECLARE_WAITQUEUE(wait, current);

	__set_current_state(TASK_UNINTERRUPTIBLE);
	add_wait_queue(&pkmap_map_wait, &wait);
	spin_unlock(&kmap_lock);
	schedule();
	remove_wait_queue(&pkmap_map_wait, &wait);
	spin_lock(&kmap_lock);

	/* Somebody else might have mapped it while we slept */
	if (page_address(page))
	return (unsigned long)page_address(page);

	/* Re-start */
	goto start;
	}
	}
	vaddr = PKMAP_ADDR(last_pkmap_nr);
	set_pte_at(&init_mm, vaddr,
	&(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

	pkmap_count[last_pkmap_nr] = 1;
	set_page_address(page, (void *)vaddr);

	return vaddr;
	}

	void fastcall kmap_high(struct page page)
	{
	unsigned long vaddr;

	/*
	* For highmem pages, we can't trust "virtual" until
	* after we have the lock.
	*
	* We cannot call this from interrupts, as it may block
	*/
	spin_lock(&kmap_lock);
	vaddr = (unsigned long)page_address(page);
	if (!vaddr)
	vaddr = map_new_virtual(page);
	pkmap_count[PKMAP_NR(vaddr)]++;
	if (pkmap_count[PKMAP_NR(vaddr)] < 2)
	BUG();
	spin_unlock(&kmap_lock);
	return (void*) vaddr;
	}

	EXPORT_SYMBOL(kmap_high);

	void fastcall kunmap_high(struct page *page)
	{
	unsigned long vaddr;
	unsigned long nr;
	int need_wakeup;

	spin_lock(&kmap_lock);
	vaddr = (unsigned long)page_address(page);
	if (!vaddr)
	BUG();
	nr = PKMAP_NR(vaddr);

	/*
	* A count must never go down to zero
	* without a TLB flush!
	*/
	need_wakeup = 0;
	switch (--pkmap_count[nr]) {
	case 0:
	BUG();
	case 1:
	/*
	* Avoid an unnecessary wake_up() function call.
	* The common case is pkmap_count[] == 1, but
	* no waiters.
	* The tasks queued in the wait-queue are guarded
	* by both the lock in the wait-queue-head and by
	* the kmap_lock. As the kmap_lock is held here,
	* no need for the wait-queue-head's lock. Simply
	* test if the queue is empty.
	*/
	need_wakeup = waitqueue_active(&pkmap_map_wait);
	}
	spin_unlock(&kmap_lock);

	/* do wake-up, if needed, race-free outside of the spin lock */
	if (need_wakeup)
	wake_up(&pkmap_map_wait);
	}

	EXPORT_SYMBOL(kunmap_high);

	#define POOL_SIZE 64

	static __init int init_emergency_pool(void)
	{
	struct sysinfo i;
	si_meminfo(&i);
	si_swapinfo(&i);

	if (!i.totalhigh)
	return 0;

	page_pool = mempool_create(POOL_SIZE, page_pool_alloc, page_pool_free, NULL);
	if (!page_pool)
	BUG();
	printk("highmem bounce pool size: %d pages\n", POOL_SIZE);

	return 0;
	}

	__initcall(init_emergency_pool);

	/*
	* highmem version, map in to vec
	*/
	static void bounce_copy_vec(struct bio_vec to, unsigned char vfrom)
	{
	unsigned long flags;
	unsigned char *vto;

	local_irq_save(flags);
	vto = kmap_atomic(to->bv_page, KM_BOUNCE_READ);
	memcpy(vto + to->bv_offset, vfrom, to->bv_len);
	kunmap_atomic(vto, KM_BOUNCE_READ);
	local_irq_restore(flags);
	}

	#else /* CONFIG_HIGHMEM */

	#define bounce_copy_vec(to, vfrom) \
	memcpy(page_address((to)->bv_page) + (to)->bv_offset, vfrom, (to)->bv_len)

	#endif

	#define ISA_POOL_SIZE 16

	/*
	* gets called "every" time someone init's a queue with BLK_BOUNCE_ISA
	* as the max address, so check if the pool has already been created.
	*/
	int init_emergency_isa_pool(void)
	{
	if (isa_page_pool)
	return 0;

	isa_page_pool = mempool_create(ISA_POOL_SIZE, page_pool_alloc, page_pool_free, (void *) __GFP_DMA);
	if (!isa_page_pool)
	BUG();

	printk("isa bounce pool size: %d pages\n", ISA_POOL_SIZE);
	return 0;
	}

	/*
	* Simple bounce buffer support for highmem pages. Depending on the
	* queue gfp mask set, *to may or may not be a highmem page. kmap it
	* always, it will do the Right Thing
	*/
	static void copy_to_high_bio_irq(struct bio to, struct bio from)
	{
	unsigned char *vfrom;
	struct bio_vec tovec, fromvec;
	int i;

	__bio_for_each_segment(tovec, to, i, 0) {
	fromvec = from->bi_io_vec + i;

	/*
	* not bounced
	*/
	if (tovec->bv_page == fromvec->bv_page)
	continue;

	/*
	* fromvec->bv_offset and fromvec->bv_len might have been
	* modified by the block layer, so use the original copy,
	* bounce_copy_vec already uses tovec->bv_len
	*/
	vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;

	flush_dcache_page(tovec->bv_page);
	bounce_copy_vec(tovec, vfrom);
	}
	}

	static void bounce_end_io(struct bio bio, mempool_t pool, int err)
	{
	struct bio *bio_orig = bio->bi_private;
	struct bio_vec bvec, org_vec;
	int i;

	if (test_bit(BIO_EOPNOTSUPP, &bio->bi_flags))
	set_bit(BIO_EOPNOTSUPP, &bio_orig->bi_flags);

	/*
	* free up bounce indirect pages used
	*/
	__bio_for_each_segment(bvec, bio, i, 0) {
	org_vec = bio_orig->bi_io_vec + i;
	if (bvec->bv_page == org_vec->bv_page)
	continue;

	mempool_free(bvec->bv_page, pool);
	dec_page_state(nr_bounce);
	}

	bio_endio(bio_orig, bio_orig->bi_size, err);
	bio_put(bio);
	}

	static int bounce_end_io_write(struct bio *bio, unsigned int bytes_done,int err)
	{
	if (bio->bi_size)
	return 1;

	bounce_end_io(bio, page_pool, err);
	return 0;
	}

	static int bounce_end_io_write_isa(struct bio *bio, unsigned int bytes_done, int err)
	{
	if (bio->bi_size)
	return 1;

	bounce_end_io(bio, isa_page_pool, err);
	return 0;
	}

	static void __bounce_end_io_read(struct bio bio, mempool_t pool, int err)
	{
	struct bio *bio_orig = bio->bi_private;

	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
	copy_to_high_bio_irq(bio_orig, bio);

	bounce_end_io(bio, pool, err);
	}

	static int bounce_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
	{
	if (bio->bi_size)
	return 1;

	__bounce_end_io_read(bio, page_pool, err);
	return 0;
	}

	static int bounce_end_io_read_isa(struct bio *bio, unsigned int bytes_done, int err)
	{
	if (bio->bi_size)
	return 1;

	__bounce_end_io_read(bio, isa_page_pool, err);
	return 0;
	}

	static void __blk_queue_bounce(request_queue_t q, struct bio *bio_orig,
	mempool_t *pool)
	{
	struct page *page;
	struct bio *bio = NULL;
	int i, rw = bio_data_dir(*bio_orig);
	struct bio_vec to, from;

	bio_for_each_segment(from, *bio_orig, i) {
	page = from->bv_page;

	/*
	* is destination page below bounce pfn?
	*/
	if (page_to_pfn(page) < q->bounce_pfn)
	continue;

	/*
	* irk, bounce it
	*/
	if (!bio)
	bio = bio_alloc(GFP_NOIO, (*bio_orig)->bi_vcnt);

	to = bio->bi_io_vec + i;

	to->bv_page = mempool_alloc(pool, q->bounce_gfp);
	to->bv_len = from->bv_len;
	to->bv_offset = from->bv_offset;
	inc_page_state(nr_bounce);

	if (rw == WRITE) {
	char vto, vfrom;

	flush_dcache_page(from->bv_page);
	vto = page_address(to->bv_page) + to->bv_offset;
	vfrom = kmap(from->bv_page) + from->bv_offset;
	memcpy(vto, vfrom, to->bv_len);
	kunmap(from->bv_page);
	}
	}

	/*
	* no pages bounced
	*/
	if (!bio)
	return;

	/*
	* at least one page was bounced, fill in possible non-highmem
	* pages
	*/
	__bio_for_each_segment(from, *bio_orig, i, 0) {
	to = bio_iovec_idx(bio, i);
	if (!to->bv_page) {
	to->bv_page = from->bv_page;
	to->bv_len = from->bv_len;
	to->bv_offset = from->bv_offset;
	}
	}

	bio->bi_bdev = (*bio_orig)->bi_bdev;
	bio->bi_flags \|= (1 << BIO_BOUNCED);
	bio->bi_sector = (*bio_orig)->bi_sector;
	bio->bi_rw = (*bio_orig)->bi_rw;

	bio->bi_vcnt = (*bio_orig)->bi_vcnt;
	bio->bi_idx = (*bio_orig)->bi_idx;
	bio->bi_size = (*bio_orig)->bi_size;

	if (pool == page_pool) {
	bio->bi_end_io = bounce_end_io_write;
	if (rw == READ)
	bio->bi_end_io = bounce_end_io_read;
	} else {
	bio->bi_end_io = bounce_end_io_write_isa;
	if (rw == READ)
	bio->bi_end_io = bounce_end_io_read_isa;
	}

	bio->bi_private = *bio_orig;
	*bio_orig = bio;
	}

	void blk_queue_bounce(request_queue_t q, struct bio *bio_orig)
	{
	mempool_t *pool;

	/*
	* for non-isa bounce case, just check if the bounce pfn is equal
	* to or bigger than the highest pfn in the system -- in that case,
	* don't waste time iterating over bio segments
	*/
	if (!(q->bounce_gfp & GFP_DMA)) {
	if (q->bounce_pfn >= blk_max_pfn)
	return;
	pool = page_pool;
	} else {
	BUG_ON(!isa_page_pool);
	pool = isa_page_pool;
	}

	/*
	* slow path
	*/
	__blk_queue_bounce(q, bio_orig, pool);
	}

	EXPORT_SYMBOL(blk_queue_bounce);

	#if defined(HASHED_PAGE_VIRTUAL)

	#define PA_HASH_ORDER 7

	/*
	* Describes one page->virtual association
	*/
	struct page_address_map {
	struct page *page;
	void *virtual;
	struct list_head list;
	};

	/*
	* page_address_map freelist, allocated from page_address_maps.
	*/
	static struct list_head page_address_pool; /* freelist */
	static spinlock_t pool_lock; /* protects page_address_pool */

	/*
	* Hash table bucket
	*/
	static struct page_address_slot {
	struct list_head lh; /* List of page_address_maps */
	spinlock_t lock; /* Protect this bucket's list */
	} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];

	static struct page_address_slot page_slot(struct page page)
	{
	return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
	}

	void page_address(struct page page)
	{
	unsigned long flags;
	void *ret;
	struct page_address_slot *pas;

	if (!PageHighMem(page))
	return lowmem_page_address(page);

	pas = page_slot(page);
	ret = NULL;
	spin_lock_irqsave(&pas->lock, flags);
	if (!list_empty(&pas->lh)) {
	struct page_address_map *pam;

	list_for_each_entry(pam, &pas->lh, list) {
	if (pam->page == page) {
	ret = pam->virtual;
	goto done;
	}
	}
	}
	done:
	spin_unlock_irqrestore(&pas->lock, flags);
	return ret;
	}

	EXPORT_SYMBOL(page_address);

	void set_page_address(struct page page, void virtual)
	{
	unsigned long flags;
	struct page_address_slot *pas;
	struct page_address_map *pam;

	BUG_ON(!PageHighMem(page));

	pas = page_slot(page);
	if (virtual) { /* Add */
	BUG_ON(list_empty(&page_address_pool));

	spin_lock_irqsave(&pool_lock, flags);
	pam = list_entry(page_address_pool.next,
	struct page_address_map, list);
	list_del(&pam->list);
	spin_unlock_irqrestore(&pool_lock, flags);

	pam->page = page;
	pam->virtual = virtual;

	spin_lock_irqsave(&pas->lock, flags);
	list_add_tail(&pam->list, &pas->lh);
	spin_unlock_irqrestore(&pas->lock, flags);
	} else { /* Remove */
	spin_lock_irqsave(&pas->lock, flags);
	list_for_each_entry(pam, &pas->lh, list) {
	if (pam->page == page) {
	list_del(&pam->list);
	spin_unlock_irqrestore(&pas->lock, flags);
	spin_lock_irqsave(&pool_lock, flags);
	list_add_tail(&pam->list, &page_address_pool);
	spin_unlock_irqrestore(&pool_lock, flags);
	goto done;
	}
	}
	spin_unlock_irqrestore(&pas->lock, flags);
	}
	done:
	return;
	}

	static struct page_address_map page_address_maps[LAST_PKMAP];

	void __init page_address_init(void)
	{
	int i;

	INIT_LIST_HEAD(&page_address_pool);
	for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
	list_add(&page_address_maps[i].list, &page_address_pool);
	for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
	INIT_LIST_HEAD(&page_address_htable[i].lh);
	spin_lock_init(&page_address_htable[i].lock);
	}
	spin_lock_init(&pool_lock);
	}

	#endif /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */