Beispiel #1
0
/*
 * Free the swap entry like above, but also try to
 * free the page cache entry if it is the last user.
 */
void free_swap_and_cache(swp_entry_t entry)
{
	struct swap_info_struct * p;
	struct page *page = NULL;

	if (is_migration_entry(entry))
		return;

	p = swap_info_get(entry);
	if (p) {
		if (swap_entry_free(p, swp_offset(entry)) == 1) {
			page = find_get_page(&swapper_space, entry.val);
			if (page && unlikely(TestSetPageLocked(page))) {
				page_cache_release(page);
				page = NULL;
			}
		}
		spin_unlock(&swap_lock);
	}
	if (page) {
		int one_user;

		BUG_ON(PagePrivate(page));
		one_user = (page_count(page) == 2);
		/* Only cache user (+us), or swap space full? Free it! */
		/* Also recheck PageSwapCache after page is locked (above) */
		if (PageSwapCache(page) && !PageWriteback(page) &&
					(one_user || vm_swap_full())) {
			delete_from_swap_cache(page);
			SetPageDirty(page);
		}
		unlock_page(page);
		page_cache_release(page);
	}
}
Beispiel #2
0
/*
 * Trying to stop swapping from a file is fraught with races, so
 * we repeat quite a bit here when we have to pause. swapoff()
 * isn't exactly timing-critical, so who cares (but this is /really/
 * inefficient, ugh).
 *
 * We return 1 after having slept, which makes the process start over
 * from the beginning for this process..
 */
static inline int unuse_pte(struct vm_area_struct * vma, unsigned long address,
	pte_t *dir, unsigned int type, unsigned long page)
{
	pte_t pte = *dir;

	if (pte_none(pte))
		return 0;
	if (pte_present(pte)) {
		unsigned long page_nr = MAP_NR(pte_page(pte));
		if (page_nr >= MAP_NR(high_memory))
			return 0;
		if (!in_swap_cache(page_nr))
			return 0;
		if (SWP_TYPE(in_swap_cache(page_nr)) != type)
			return 0;
		delete_from_swap_cache(page_nr);
		set_pte(dir, pte_mkdirty(pte));
		return 0;
	}
	if (SWP_TYPE(pte_val(pte)) != type)
		return 0;
	read_swap_page(pte_val(pte), (char *) page);
#if 0 /* Is this really needed here, hasn't it been solved elsewhere? */
	flush_page_to_ram(page);
#endif
	if (pte_val(*dir) != pte_val(pte)) {
		free_page(page);
		return 1;
	}
	set_pte(dir, pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot))));
	flush_tlb_page(vma, address);
	++vma->vm_mm->rss;
	swap_free(pte_val(pte));
	return 1;
}
Beispiel #3
0
static inline void copy_one_pte(pte_t * old_pte, pte_t * new_pte, int cow)
{
	pte_t pte = *old_pte;
	unsigned long page_nr;

	if (pte_none(pte))
		return;
	if (!pte_present(pte)) {
		swap_duplicate(pte_val(pte));
		set_pte(new_pte, pte);
		return;
	}
	page_nr = MAP_NR(pte_page(pte));
	if (page_nr >= MAP_NR(high_memory) || PageReserved(mem_map+page_nr)) {
		set_pte(new_pte, pte);
		return;
	}
	if (cow)
		pte = pte_wrprotect(pte);
	if (delete_from_swap_cache(page_nr))
		pte = pte_mkdirty(pte);
	set_pte(new_pte, pte_mkold(pte));
	set_pte(old_pte, pte);
	mem_map[page_nr].count++;
}
Beispiel #4
0
/*
 * Strange swizzling function for shmem_getpage (and shmem_unuse)
 */
int move_from_swap_cache(struct page *page, unsigned long index,
		struct address_space *mapping)
{
	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
	if (!err) {
		delete_from_swap_cache(page);
		/* shift page from clean_pages to dirty_pages list */
		ClearPageDirty(page);
		set_page_dirty(page);
	}
	return err;
}
Beispiel #5
0
void free_page_and_swap_cache(unsigned long addr)
{
	struct page *page = mem_map + MAP_NR(addr);

	/* 
	 * If we are the only user, then free up the swap cache. 
	 */
	if (PageSwapCache(page) && !is_page_shared(page)) {
		delete_from_swap_cache(page);
	}
	
	__free_page(page);
}
Beispiel #6
0
/*
 * Free the swap entry like above, but also try to
 * free the page cache entry if it is the last user.
 */
void free_swap_and_cache(swp_entry_t entry)
{
	struct swap_info_struct * p;
	struct page *page = NULL;

	p = swap_info_get(entry);
	if (p) {
		if (swap_entry_free(p, SWP_OFFSET(entry)) == 1)
			page = find_trylock_page(&swapper_space, entry.val);
		swap_info_put(p);
	}
	if (page) {
		page_cache_get(page);
		/* Only cache user (+us), or swap space full? Free it! */
		if (page_count(page) - !!page->buffers == 2 || vm_swap_full()) {
			delete_from_swap_cache(page);
			SetPageDirty(page);
		}
		UnlockPage(page);
		page_cache_release(page);
	}
}
Beispiel #7
0
/*
 * We completely avoid races by reading each swap page in advance,
 * and then search for the process using it.  All the necessary
 * page table adjustments can then be made atomically.
 */
static int try_to_unuse(unsigned int type)
{
	struct swap_info_struct * si = &swap_info[type];
	struct mm_struct *start_mm;
	unsigned short *swap_map;
	unsigned short swcount;
	struct page *page;
	swp_entry_t entry;
	int i = 0;
	int retval = 0;
	int reset_overflow = 0;

	/*
	 * When searching mms for an entry, a good strategy is to
	 * start at the first mm we freed the previous entry from
	 * (though actually we don't notice whether we or coincidence
	 * freed the entry).  Initialize this start_mm with a hold.
	 *
	 * A simpler strategy would be to start at the last mm we
	 * freed the previous entry from; but that would take less
	 * advantage of mmlist ordering (now preserved by swap_out()),
	 * which clusters forked address spaces together, most recent
	 * child immediately after parent.  If we race with dup_mmap(),
	 * we very much want to resolve parent before child, otherwise
	 * we may miss some entries: using last mm would invert that.
	 */
	start_mm = &init_mm;
	atomic_inc(&init_mm.mm_users);

	/*
	 * Keep on scanning until all entries have gone.  Usually,
	 * one pass through swap_map is enough, but not necessarily:
	 * mmput() removes mm from mmlist before exit_mmap() and its
	 * zap_page_range().  That's not too bad, those entries are
	 * on their way out, and handled faster there than here.
	 * do_munmap() behaves similarly, taking the range out of mm's
	 * vma list before zap_page_range().  But unfortunately, when
	 * unmapping a part of a vma, it takes the whole out first,
	 * then reinserts what's left after (might even reschedule if
	 * open() method called) - so swap entries may be invisible
	 * to swapoff for a while, then reappear - but that is rare.
	 */
	while ((i = find_next_to_unuse(si, i))) {
		/* 
		 * Get a page for the entry, using the existing swap
		 * cache page if there is one.  Otherwise, get a clean
		 * page and read the swap into it. 
		 */
		swap_map = &si->swap_map[i];
		entry = SWP_ENTRY(type, i);
		page = read_swap_cache_async(entry);
		if (!page) {
			/*
			 * Either swap_duplicate() failed because entry
			 * has been freed independently, and will not be
			 * reused since sys_swapoff() already disabled
			 * allocation from here, or alloc_page() failed.
			 */
			if (!*swap_map)
				continue;
			retval = -ENOMEM;
			break;
		}

		/*
		 * Don't hold on to start_mm if it looks like exiting.
		 */
		if (atomic_read(&start_mm->mm_users) == 1) {
			mmput(start_mm);
			start_mm = &init_mm;
			atomic_inc(&init_mm.mm_users);
		}

		/*
		 * Wait for and lock page.  When do_swap_page races with
		 * try_to_unuse, do_swap_page can handle the fault much
		 * faster than try_to_unuse can locate the entry.  This
		 * apparently redundant "wait_on_page" lets try_to_unuse
		 * defer to do_swap_page in such a case - in some tests,
		 * do_swap_page and try_to_unuse repeatedly compete.
		 */
		wait_on_page(page);
		lock_page(page);

		/*
		 * Remove all references to entry, without blocking.
		 * Whenever we reach init_mm, there's no address space
		 * to search, but use it as a reminder to search shmem.
		 */
		swcount = *swap_map;
		if (swcount > 1) {
			flush_page_to_ram(page);
			if (start_mm == &init_mm)
				shmem_unuse(entry, page);
			else
				unuse_process(start_mm, entry, page);
		}
		if (*swap_map > 1) {
			int set_start_mm = (*swap_map >= swcount);
			struct list_head *p = &start_mm->mmlist;
			struct mm_struct *new_start_mm = start_mm;
			struct mm_struct *mm;

			spin_lock(&mmlist_lock);
			while (*swap_map > 1 &&
					(p = p->next) != &start_mm->mmlist) {
				mm = list_entry(p, struct mm_struct, mmlist);
				swcount = *swap_map;
				if (mm == &init_mm) {
					set_start_mm = 1;
					shmem_unuse(entry, page);
				} else
					unuse_process(mm, entry, page);
				if (set_start_mm && *swap_map < swcount) {
					new_start_mm = mm;
					set_start_mm = 0;
				}
			}
			atomic_inc(&new_start_mm->mm_users);
			spin_unlock(&mmlist_lock);
			mmput(start_mm);
			start_mm = new_start_mm;
		}

		/*
		 * How could swap count reach 0x7fff when the maximum
		 * pid is 0x7fff, and there's no way to repeat a swap
		 * page within an mm (except in shmem, where it's the
		 * shared object which takes the reference count)?
		 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
		 *
		 * If that's wrong, then we should worry more about
		 * exit_mmap() and do_munmap() cases described above:
		 * we might be resetting SWAP_MAP_MAX too early here.
		 * We know "Undead"s can happen, they're okay, so don't
		 * report them; but do report if we reset SWAP_MAP_MAX.
		 */
		if (*swap_map == SWAP_MAP_MAX) {
			swap_list_lock();
			swap_device_lock(si);
			nr_swap_pages++;
			*swap_map = 1;
			swap_device_unlock(si);
			swap_list_unlock();
			reset_overflow = 1;
		}

		/*
		 * If a reference remains (rare), we would like to leave
		 * the page in the swap cache; but try_to_swap_out could
		 * then re-duplicate the entry once we drop page lock,
		 * so we might loop indefinitely; also, that page could
		 * not be swapped out to other storage meanwhile.  So:
		 * delete from cache even if there's another reference,
		 * after ensuring that the data has been saved to disk -
		 * since if the reference remains (rarer), it will be
		 * read from disk into another page.  Splitting into two
		 * pages would be incorrect if swap supported "shared
		 * private" pages, but they are handled by tmpfs files.
		 * Note shmem_unuse already deleted its from swap cache.
		 */
		if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
			rw_swap_page(WRITE, page);
			lock_page(page);
		}
		if (PageSwapCache(page))
			delete_from_swap_cache(page);

		/*
		 * So we could skip searching mms once swap count went
		 * to 1, we did not mark any present ptes as dirty: must
		 * mark page dirty so try_to_swap_out will preserve it.
		 */
		SetPageDirty(page);
		UnlockPage(page);
		page_cache_release(page);

		/*
		 * Make sure that we aren't completely killing
		 * interactive performance.  Interruptible check on
		 * signal_pending() would be nice, but changes the spec?
		 */
		if (current->need_resched)
			schedule();
	}
Beispiel #8
0
/*
 * We completely avoid races by reading each swap page in advance,
 * and then search for the process using it.  All the necessary
 * page table adjustments can then be made atomically.
 */
static int try_to_unuse(unsigned int type)
{
	struct swap_info_struct * si = &swap_info[type];
	struct mm_struct *start_mm;
	unsigned short *swap_map;
	unsigned short swcount;
	struct page *page;
	swp_entry_t entry;
	unsigned int i = 0;
	int retval = 0;
	int reset_overflow = 0;
	int shmem;

	/*
	 * When searching mms for an entry, a good strategy is to
	 * start at the first mm we freed the previous entry from
	 * (though actually we don't notice whether we or coincidence
	 * freed the entry).  Initialize this start_mm with a hold.
	 *
	 * A simpler strategy would be to start at the last mm we
	 * freed the previous entry from; but that would take less
	 * advantage of mmlist ordering, which clusters forked mms
	 * together, child after parent.  If we race with dup_mmap(), we
	 * prefer to resolve parent before child, lest we miss entries
	 * duplicated after we scanned child: using last mm would invert
	 * that.  Though it's only a serious concern when an overflowed
	 * swap count is reset from SWAP_MAP_MAX, preventing a rescan.
	 */
	start_mm = &init_mm;
	atomic_inc(&init_mm.mm_users);

	/*
	 * Keep on scanning until all entries have gone.  Usually,
	 * one pass through swap_map is enough, but not necessarily:
	 * there are races when an instance of an entry might be missed.
	 */
	while ((i = find_next_to_unuse(si, i)) != 0) {
		if (signal_pending(current)) {
			retval = -EINTR;
			break;
		}

		/* 
		 * Get a page for the entry, using the existing swap
		 * cache page if there is one.  Otherwise, get a clean
		 * page and read the swap into it. 
		 */
		swap_map = &si->swap_map[i];
		entry = swp_entry(type, i);
		page = read_swap_cache_async(entry, NULL, 0);
		if (!page) {
			/*
			 * Either swap_duplicate() failed because entry
			 * has been freed independently, and will not be
			 * reused since sys_swapoff() already disabled
			 * allocation from here, or alloc_page() failed.
			 */
			if (!*swap_map)
				continue;
			retval = -ENOMEM;
			break;
		}

		/*
		 * Don't hold on to start_mm if it looks like exiting.
		 */
		if (atomic_read(&start_mm->mm_users) == 1) {
			mmput(start_mm);
			start_mm = &init_mm;
			atomic_inc(&init_mm.mm_users);
		}

		/*
		 * Wait for and lock page.  When do_swap_page races with
		 * try_to_unuse, do_swap_page can handle the fault much
		 * faster than try_to_unuse can locate the entry.  This
		 * apparently redundant "wait_on_page_locked" lets try_to_unuse
		 * defer to do_swap_page in such a case - in some tests,
		 * do_swap_page and try_to_unuse repeatedly compete.
		 */
		wait_on_page_locked(page);
		wait_on_page_writeback(page);
		lock_page(page);
		wait_on_page_writeback(page);

		/*
		 * Remove all references to entry.
		 * Whenever we reach init_mm, there's no address space
		 * to search, but use it as a reminder to search shmem.
		 */
		shmem = 0;
		swcount = *swap_map;
		if (swcount > 1) {
			if (start_mm == &init_mm)
				shmem = shmem_unuse(entry, page);
			else
				retval = unuse_mm(start_mm, entry, page);
		}
		if (*swap_map > 1) {
			int set_start_mm = (*swap_map >= swcount);
			struct list_head *p = &start_mm->mmlist;
			struct mm_struct *new_start_mm = start_mm;
			struct mm_struct *prev_mm = start_mm;
			struct mm_struct *mm;

			atomic_inc(&new_start_mm->mm_users);
			atomic_inc(&prev_mm->mm_users);
			spin_lock(&mmlist_lock);
			while (*swap_map > 1 && !retval &&
					(p = p->next) != &start_mm->mmlist) {
				mm = list_entry(p, struct mm_struct, mmlist);
				if (!atomic_inc_not_zero(&mm->mm_users))
					continue;
				spin_unlock(&mmlist_lock);
				mmput(prev_mm);
				prev_mm = mm;

				cond_resched();

				swcount = *swap_map;
				if (swcount <= 1)
					;
				else if (mm == &init_mm) {
					set_start_mm = 1;
					shmem = shmem_unuse(entry, page);
				} else
					retval = unuse_mm(mm, entry, page);
				if (set_start_mm && *swap_map < swcount) {
					mmput(new_start_mm);
					atomic_inc(&mm->mm_users);
					new_start_mm = mm;
					set_start_mm = 0;
				}
				spin_lock(&mmlist_lock);
			}
			spin_unlock(&mmlist_lock);
			mmput(prev_mm);
			mmput(start_mm);
			start_mm = new_start_mm;
		}
		if (retval) {
			unlock_page(page);
			page_cache_release(page);
			break;
		}

		/*
		 * How could swap count reach 0x7fff when the maximum
		 * pid is 0x7fff, and there's no way to repeat a swap
		 * page within an mm (except in shmem, where it's the
		 * shared object which takes the reference count)?
		 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
		 *
		 * If that's wrong, then we should worry more about
		 * exit_mmap() and do_munmap() cases described above:
		 * we might be resetting SWAP_MAP_MAX too early here.
		 * We know "Undead"s can happen, they're okay, so don't
		 * report them; but do report if we reset SWAP_MAP_MAX.
		 */
		if (*swap_map == SWAP_MAP_MAX) {
			spin_lock(&swap_lock);
			*swap_map = 1;
			spin_unlock(&swap_lock);
			reset_overflow = 1;
		}

		/*
		 * If a reference remains (rare), we would like to leave
		 * the page in the swap cache; but try_to_unmap could
		 * then re-duplicate the entry once we drop page lock,
		 * so we might loop indefinitely; also, that page could
		 * not be swapped out to other storage meanwhile.  So:
		 * delete from cache even if there's another reference,
		 * after ensuring that the data has been saved to disk -
		 * since if the reference remains (rarer), it will be
		 * read from disk into another page.  Splitting into two
		 * pages would be incorrect if swap supported "shared
		 * private" pages, but they are handled by tmpfs files.
		 *
		 * Note shmem_unuse already deleted a swappage from
		 * the swap cache, unless the move to filepage failed:
		 * in which case it left swappage in cache, lowered its
		 * swap count to pass quickly through the loops above,
		 * and now we must reincrement count to try again later.
		 */
		if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
			struct writeback_control wbc = {
				.sync_mode = WB_SYNC_NONE,
			};

			swap_writepage(page, &wbc);
			lock_page(page);
			wait_on_page_writeback(page);
		}
		if (PageSwapCache(page)) {
			if (shmem)
				swap_duplicate(entry);
			else
				delete_from_swap_cache(page);
		}

		/*
		 * So we could skip searching mms once swap count went
		 * to 1, we did not mark any present ptes as dirty: must
		 * mark page dirty so shrink_page_list will preserve it.
		 */
		SetPageDirty(page);
		unlock_page(page);
		page_cache_release(page);

		/*
		 * Make sure that we aren't completely killing
		 * interactive performance.
		 */
		cond_resched();
	}
Beispiel #9
0
static int unswap_by_move(unsigned short *map, unsigned long max,
			  unsigned long start, unsigned long n_pages)
{
	struct task_struct *p;
	unsigned long entry, rover = (start == 1) ? n_pages+1 : 1;
	unsigned long i, j;

	DPRINTK( "unswapping %lu..%lu by moving in swap\n",
			 start, start+n_pages-1 );
	
	/* can free the allocated pages by moving them to other swap pages */
	for( i = start; i < start+n_pages; ++i ) {
		if (!map[i]) {
			map[i] = SWAP_MAP_BAD;
			DPRINTK( "unswap: page %lu was free\n", i );
			continue;
		}
		else if (map[i] == SWAP_MAP_BAD) {
			printk( KERN_ERR "get_stram_region: page %lu already "
					"reserved??\n", i );
		}
		DPRINTK( "unswap: page %lu is alloced, count=%u\n", i, map[i] );

		/* find a free page not in our region */
		for( j = rover; j != rover-1; j = (j == max-1) ? 1 : j+1 ) {
			if (j >= start && j < start+n_pages)
				continue;
			if (!map[j]) {
				rover = j+1;
				break;
			}
		}
		if (j == rover-1) {
			printk( KERN_ERR "get_stram_region: not enough free swap "
					"pages now??\n" );
			return( -ENOMEM );
		}
		DPRINTK( "unswap: map[i=%lu]=%u map[j=%lu]=%u nr_swap=%u\n",
				 i, map[i], j, map[j], nr_swap_pages );
		
		--nr_swap_pages;
		entry = SWP_ENTRY( stram_swap_type, j );
		if (stram_swap_info->lowest_bit == j)
			stram_swap_info->lowest_bit++;
		if (stram_swap_info->highest_bit == j)
			stram_swap_info->highest_bit--;
		
		memcpy( SWAP_ADDR(j), SWAP_ADDR(i), PAGE_SIZE );
#ifdef DO_PROC
		stat_swap_move++;
#endif

		while( map[i] ) {
			read_lock(&tasklist_lock);
			for_each_task(p) {
				if (unswap_process( p->mm, SWP_ENTRY( stram_swap_type, i ),
									entry, 1 )) {
					read_unlock(&tasklist_lock);
					map[j]++;
					goto repeat;
				}
			}
			read_unlock(&tasklist_lock);
			if (map[i] && map[i] != SWAP_MAP_MAX) {
				printk( KERN_ERR "get_stram_region: ST-RAM swap page %lu "
						"not used by any process\n", i );
				/* quit while loop and overwrite bad map entry */
				break;
			}
			else if (!map[i]) {
				/* somebody else must have swapped in that page, so free the
				 * new one (we're moving to) */
				DPRINTK( "unswap: map[i] became 0, also clearing map[j]\n" );
				map[j] = 0;
			}
		  repeat:
		}

		DPRINTK( "unswap: map[i=%lu]=%u map[j=%lu]=%u nr_swap=%u\n",
				 i, map[i], j, map[j], nr_swap_pages );
		map[i] = SWAP_MAP_BAD;
		if (stram_swap_info->lowest_bit == i)
			stram_swap_info->lowest_bit++;
		if (stram_swap_info->highest_bit == i)
			stram_swap_info->highest_bit--;
		--nr_swap_pages;
	}
	return( 0 );
}
#endif

static int unswap_by_read(unsigned short *map, unsigned long max,
			  unsigned long start, unsigned long n_pages)
{
	struct task_struct *p;
	unsigned long entry, page;
	unsigned long i;
	struct page *page_map;

	DPRINTK( "unswapping %lu..%lu by reading in\n",
			 start, start+n_pages-1 );

	for( i = start; i < start+n_pages; ++i ) {
		if (map[i] == SWAP_MAP_BAD) {
			printk( KERN_ERR "get_stram_region: page %lu already "
					"reserved??\n", i );
			continue;
		}

		if (map[i]) {
			entry = SWP_ENTRY(stram_swap_type, i);
			DPRINTK("unswap: map[i=%lu]=%u nr_swap=%u\n",
				i, map[i], nr_swap_pages);

			/* Get a page for the entry, using the existing
			   swap cache page if there is one.  Otherwise,
			   get a clean page and read the swap into it. */
			page_map = read_swap_cache(entry);
			if (page_map) {
				page = page_address(page_map);
				read_lock(&tasklist_lock);
				for_each_task(p)
					unswap_process(p->mm, entry, page
						       /* , 0 */);
				read_unlock(&tasklist_lock);
				shm_unuse(entry, page);
				/* Now get rid of the extra reference to
				   the temporary page we've been using. */
				if (PageSwapCache(page_map))
					delete_from_swap_cache(page_map);
				__free_page(page_map);
	#ifdef DO_PROC
				stat_swap_force++;
	#endif
			}
			else if (map[i])
				return -ENOMEM;
		}

		DPRINTK( "unswap: map[i=%lu]=%u nr_swap=%u\n",
				 i, map[i], nr_swap_pages );
		map[i] = SWAP_MAP_BAD;
		if (stram_swap_info->lowest_bit == i)
			stram_swap_info->lowest_bit++;
		if (stram_swap_info->highest_bit == i)
			stram_swap_info->highest_bit--;
		--nr_swap_pages;
	}

	return 0;
}

/*
 * reserve a region in ST-RAM swap space for an allocation
 */
static void *get_stram_region( unsigned long n_pages )
{
	unsigned short *map = stram_swap_info->swap_map;
	unsigned long max = stram_swap_info->max;
	unsigned long start, total_free, region_free;
	int err;
	void *ret = NULL;
	
	DPRINTK( "get_stram_region(n_pages=%lu)\n", n_pages );

	down(&stram_swap_sem);

	/* disallow writing to the swap device now */
	stram_swap_info->flags = SWP_USED;

	/* find a region of n_pages pages in the swap space including as much free
	 * pages as possible (and excluding any already-reserved pages). */
	if (!(start = find_free_region( n_pages, &total_free, &region_free )))
		goto end;
	DPRINTK( "get_stram_region: region starts at %lu, has %lu free pages\n",
			 start, region_free );

#if 0
	err = ((total_free-region_free >= n_pages-region_free) ?
		   unswap_by_move( map, max, start, n_pages ) :
		   unswap_by_read( map, max, start, n_pages ));
#else
	err = unswap_by_read(map, max, start, n_pages);
#endif

	if (err)
		goto end;

	ret = SWAP_ADDR(start);
  end:
	/* allow using swap device again */
	stram_swap_info->flags = SWP_WRITEOK;
	up(&stram_swap_sem);
	DPRINTK( "get_stram_region: returning %p\n", ret );
	return( ret );
}