highmem.c revision 920c7a5d0c94b8ce740f1d76fa06422f2a95a757 
1/*
2 * High memory handling common code and variables.
3 *
4 * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
5 *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
6 *
7 *
8 * Redesigned the x86 32-bit VM architecture to deal with
9 * 64-bit physical space. With current x86 CPUs this
10 * means up to 64 Gigabytes physical RAM.
11 *
12 * Rewrote high memory support to move the page cache into
13 * high memory. Implemented permanent (schedulable) kmaps
14 * based on Linus' idea.
15 *
16 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
17 */
18
19#include <linux/mm.h>
20#include <linux/module.h>
21#include <linux/swap.h>
22#include <linux/bio.h>
23#include <linux/pagemap.h>
24#include <linux/mempool.h>
25#include <linux/blkdev.h>
26#include <linux/init.h>
27#include <linux/hash.h>
28#include <linux/highmem.h>
29#include <linux/blktrace_api.h>
30#include <asm/tlbflush.h>
31
32/*
33 * Virtual_count is not a pure "count".
34 *  0 means that it is not mapped, and has not been mapped
35 *    since a TLB flush - it is usable.
36 *  1 means that there are no users, but it has been mapped
37 *    since the last TLB flush - so we can't use it.
38 *  n means that there are (n-1) current users of it.
39 */
40#ifdef CONFIG_HIGHMEM
41
42unsigned long totalhigh_pages __read_mostly;
43
44unsigned int nr_free_highpages (void)
45{
46	pg_data_t *pgdat;
47	unsigned int pages = 0;
48
49	for_each_online_pgdat(pgdat) {
50		pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
51			NR_FREE_PAGES);
52		if (zone_movable_is_highmem())
53			pages += zone_page_state(
54					&pgdat->node_zones[ZONE_MOVABLE],
55					NR_FREE_PAGES);
56	}
57
58	return pages;
59}
60
61static int pkmap_count[LAST_PKMAP];
62static unsigned int last_pkmap_nr;
63static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
64
65pte_t * pkmap_page_table;
66
67static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
68
69static void flush_all_zero_pkmaps(void)
70{
71	int i;
72
73	flush_cache_kmaps();
74
75	for (i = 0; i < LAST_PKMAP; i++) {
76		struct page *page;
77
78		/*
79		 * zero means we don't have anything to do,
80		 * >1 means that it is still in use. Only
81		 * a count of 1 means that it is free but
82		 * needs to be unmapped
83		 */
84		if (pkmap_count[i] != 1)
85			continue;
86		pkmap_count[i] = 0;
87
88		/* sanity check */
89		BUG_ON(pte_none(pkmap_page_table[i]));
90
91		/*
92		 * Don't need an atomic fetch-and-clear op here;
93		 * no-one has the page mapped, and cannot get at
94		 * its virtual address (and hence PTE) without first
95		 * getting the kmap_lock (which is held here).
96		 * So no dangers, even with speculative execution.
97		 */
98		page = pte_page(pkmap_page_table[i]);
99		pte_clear(&init_mm, (unsigned long)page_address(page),
100			  &pkmap_page_table[i]);
101
102		set_page_address(page, NULL);
103	}
104	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
105}
106
107/* Flush all unused kmap mappings in order to remove stray
108   mappings. */
109void kmap_flush_unused(void)
110{
111	spin_lock(&kmap_lock);
112	flush_all_zero_pkmaps();
113	spin_unlock(&kmap_lock);
114}
115
116static inline unsigned long map_new_virtual(struct page *page)
117{
118	unsigned long vaddr;
119	int count;
120
121start:
122	count = LAST_PKMAP;
123	/* Find an empty entry */
124	for (;;) {
125		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
126		if (!last_pkmap_nr) {
127			flush_all_zero_pkmaps();
128			count = LAST_PKMAP;
129		}
130		if (!pkmap_count[last_pkmap_nr])
131			break;	/* Found a usable entry */
132		if (--count)
133			continue;
134
135		/*
136		 * Sleep for somebody else to unmap their entries
137		 */
138		{
139			DECLARE_WAITQUEUE(wait, current);
140
141			__set_current_state(TASK_UNINTERRUPTIBLE);
142			add_wait_queue(&pkmap_map_wait, &wait);
143			spin_unlock(&kmap_lock);
144			schedule();
145			remove_wait_queue(&pkmap_map_wait, &wait);
146			spin_lock(&kmap_lock);
147
148			/* Somebody else might have mapped it while we slept */
149			if (page_address(page))
150				return (unsigned long)page_address(page);
151
152			/* Re-start */
153			goto start;
154		}
155	}
156	vaddr = PKMAP_ADDR(last_pkmap_nr);
157	set_pte_at(&init_mm, vaddr,
158		   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
159
160	pkmap_count[last_pkmap_nr] = 1;
161	set_page_address(page, (void *)vaddr);
162
163	return vaddr;
164}
165
166void *kmap_high(struct page *page)
167{
168	unsigned long vaddr;
169
170	/*
171	 * For highmem pages, we can't trust "virtual" until
172	 * after we have the lock.
173	 *
174	 * We cannot call this from interrupts, as it may block
175	 */
176	spin_lock(&kmap_lock);
177	vaddr = (unsigned long)page_address(page);
178	if (!vaddr)
179		vaddr = map_new_virtual(page);
180	pkmap_count[PKMAP_NR(vaddr)]++;
181	BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
182	spin_unlock(&kmap_lock);
183	return (void*) vaddr;
184}
185
186EXPORT_SYMBOL(kmap_high);
187
188void kunmap_high(struct page *page)
189{
190	unsigned long vaddr;
191	unsigned long nr;
192	int need_wakeup;
193
194	spin_lock(&kmap_lock);
195	vaddr = (unsigned long)page_address(page);
196	BUG_ON(!vaddr);
197	nr = PKMAP_NR(vaddr);
198
199	/*
200	 * A count must never go down to zero
201	 * without a TLB flush!
202	 */
203	need_wakeup = 0;
204	switch (--pkmap_count[nr]) {
205	case 0:
206		BUG();
207	case 1:
208		/*
209		 * Avoid an unnecessary wake_up() function call.
210		 * The common case is pkmap_count[] == 1, but
211		 * no waiters.
212		 * The tasks queued in the wait-queue are guarded
213		 * by both the lock in the wait-queue-head and by
214		 * the kmap_lock.  As the kmap_lock is held here,
215		 * no need for the wait-queue-head's lock.  Simply
216		 * test if the queue is empty.
217		 */
218		need_wakeup = waitqueue_active(&pkmap_map_wait);
219	}
220	spin_unlock(&kmap_lock);
221
222	/* do wake-up, if needed, race-free outside of the spin lock */
223	if (need_wakeup)
224		wake_up(&pkmap_map_wait);
225}
226
227EXPORT_SYMBOL(kunmap_high);
228#endif
229
230#if defined(HASHED_PAGE_VIRTUAL)
231
232#define PA_HASH_ORDER	7
233
234/*
235 * Describes one page->virtual association
236 */
237struct page_address_map {
238	struct page *page;
239	void *virtual;
240	struct list_head list;
241};
242
243/*
244 * page_address_map freelist, allocated from page_address_maps.
245 */
246static struct list_head page_address_pool;	/* freelist */
247static spinlock_t pool_lock;			/* protects page_address_pool */
248
249/*
250 * Hash table bucket
251 */
252static struct page_address_slot {
253	struct list_head lh;			/* List of page_address_maps */
254	spinlock_t lock;			/* Protect this bucket's list */
255} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
256
257static struct page_address_slot *page_slot(struct page *page)
258{
259	return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
260}
261
262void *page_address(struct page *page)
263{
264	unsigned long flags;
265	void *ret;
266	struct page_address_slot *pas;
267
268	if (!PageHighMem(page))
269		return lowmem_page_address(page);
270
271	pas = page_slot(page);
272	ret = NULL;
273	spin_lock_irqsave(&pas->lock, flags);
274	if (!list_empty(&pas->lh)) {
275		struct page_address_map *pam;
276
277		list_for_each_entry(pam, &pas->lh, list) {
278			if (pam->page == page) {
279				ret = pam->virtual;
280				goto done;
281			}
282		}
283	}
284done:
285	spin_unlock_irqrestore(&pas->lock, flags);
286	return ret;
287}
288
289EXPORT_SYMBOL(page_address);
290
291void set_page_address(struct page *page, void *virtual)
292{
293	unsigned long flags;
294	struct page_address_slot *pas;
295	struct page_address_map *pam;
296
297	BUG_ON(!PageHighMem(page));
298
299	pas = page_slot(page);
300	if (virtual) {		/* Add */
301		BUG_ON(list_empty(&page_address_pool));
302
303		spin_lock_irqsave(&pool_lock, flags);
304		pam = list_entry(page_address_pool.next,
305				struct page_address_map, list);
306		list_del(&pam->list);
307		spin_unlock_irqrestore(&pool_lock, flags);
308
309		pam->page = page;
310		pam->virtual = virtual;
311
312		spin_lock_irqsave(&pas->lock, flags);
313		list_add_tail(&pam->list, &pas->lh);
314		spin_unlock_irqrestore(&pas->lock, flags);
315	} else {		/* Remove */
316		spin_lock_irqsave(&pas->lock, flags);
317		list_for_each_entry(pam, &pas->lh, list) {
318			if (pam->page == page) {
319				list_del(&pam->list);
320				spin_unlock_irqrestore(&pas->lock, flags);
321				spin_lock_irqsave(&pool_lock, flags);
322				list_add_tail(&pam->list, &page_address_pool);
323				spin_unlock_irqrestore(&pool_lock, flags);
324				goto done;
325			}
326		}
327		spin_unlock_irqrestore(&pas->lock, flags);
328	}
329done:
330	return;
331}
332
333static struct page_address_map page_address_maps[LAST_PKMAP];
334
335void __init page_address_init(void)
336{
337	int i;
338
339	INIT_LIST_HEAD(&page_address_pool);
340	for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
341		list_add(&page_address_maps[i].list, &page_address_pool);
342	for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
343		INIT_LIST_HEAD(&page_address_htable[i].lh);
344		spin_lock_init(&page_address_htable[i].lock);
345	}
346	spin_lock_init(&pool_lock);
347}
348
349#endif	/* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
350