Commit 4f89849d authored by Minchan Kim's avatar Minchan Kim Committed by Linus Torvalds
Browse files

frontswap: get rid of swap_lock dependency 



Frontswap initialization routine depends on swap_lock, which want to be
atomic about frontswap's first appearance.  IOW, frontswap is not present
and will fail all calls OR frontswap is fully functional but if new
swap_info_struct isn't registered by enable_swap_info, swap subsystem
doesn't start I/O so there is no race between init procedure and page I/O
working on frontswap.

So let's remove unnecessary swap_lock dependency.

Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
[v1: Rebased on my branch, reworked to work with backends loading late]
[v2: Added a check for !map]
[v3: Made the invalidate path follow the init path]
[v4: Address comments by Wanpeng Li <liwanp@linux.vnet.ibm.com>]
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad@darnok.org>
Signed-off-by: default avatarBob Liu <lliubbo@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andor Daam <andor.daam@googlemail.com>
Cc: Florian Schmaus <fschmaus@gmail.com>
Cc: Stefan Hengelein <ilendir@googlemail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f066ea23

include/linux/frontswap.h

+3 −3
Original line number Diff line number Diff line
@@ -23,7 +23,7 @@ extern void frontswap_writethrough(bool); 
extern void frontswap_tmem_exclusive_gets(bool);



extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);

extern void __frontswap_init(unsigned type);

extern void __frontswap_init(unsigned type, unsigned long *map);

extern int __frontswap_store(struct page *page);

extern int __frontswap_load(struct page *page);

extern void __frontswap_invalidate_page(unsigned, pgoff_t);
@@ -98,10 +98,10 @@ static inline void frontswap_invalidate_area(unsigned type) 
		__frontswap_invalidate_area(type);

}



static inline void frontswap_init(unsigned type)

static inline void frontswap_init(unsigned type, unsigned long *map)

{

	if (frontswap_enabled)

		__frontswap_init(type);

		__frontswap_init(type, map);

}



#endif /* _LINUX_FRONTSWAP_H */

mm/frontswap.c

+23 −8
Original line number Diff line number Diff line
@@ -121,9 +121,14 @@ struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops) 
	int i;



	for (i = 0; i < MAX_SWAPFILES; i++) {

		if (test_and_clear_bit(i, need_init))

		if (test_and_clear_bit(i, need_init)) {

			struct swap_info_struct *sis = swap_info[i];

			/* __frontswap_init _should_ have set it! */

			if (!sis->frontswap_map)

				return ERR_PTR(-EINVAL);

			ops->init(i);

		}

	}

	/*

	 * We MUST have frontswap_ops set _after_ the frontswap_init's

	 * have been called. Otherwise __frontswap_store might fail. Hence
@@ -156,20 +161,30 @@ EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); 
/*

 * Called when a swap device is swapon'd.

 */

void __frontswap_init(unsigned type)

void __frontswap_init(unsigned type, unsigned long *map)

{

	struct swap_info_struct *sis = swap_info[type];



	if (frontswap_ops) {

	BUG_ON(sis == NULL);

		if (sis->frontswap_map == NULL)



	/*

	 * p->frontswap is a bitmap that we MUST have to figure out which page

	 * has gone in frontswap. Without it there is no point of continuing.

	 */

	if (WARN_ON(!map))

		return;

	/*

	 * Irregardless of whether the frontswap backend has been loaded

	 * before this function or it will be later, we _MUST_ have the

	 * p->frontswap set to something valid to work properly.

	 */

	frontswap_map_set(sis, map);

	if (frontswap_ops)

		frontswap_ops->init(type);

	} else {

	else {

		BUG_ON(type > MAX_SWAPFILES);

		set_bit(type, need_init);

	}



}

EXPORT_SYMBOL(__frontswap_init);

mm/swapfile.c

+9 −8
Original line number Diff line number Diff line
@@ -1509,8 +1509,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) 
}



static void _enable_swap_info(struct swap_info_struct *p, int prio,

				unsigned char *swap_map,

				unsigned long *frontswap_map)

				unsigned char *swap_map)

{

	int i, prev;
@@ -1519,7 +1518,6 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio, 
	else

		p->prio = --least_priority;

	p->swap_map = swap_map;

	frontswap_map_set(p, frontswap_map);

	p->flags |= SWP_WRITEOK;

	atomic_long_add(p->pages, &nr_swap_pages);

	total_swap_pages += p->pages;
@@ -1542,10 +1540,10 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, 
				unsigned char *swap_map,

				unsigned long *frontswap_map)

{

	frontswap_init(p->type, frontswap_map);

	spin_lock(&swap_lock);

	spin_lock(&p->lock);

	_enable_swap_info(p, prio, swap_map, frontswap_map);

	frontswap_init(p->type);

	 _enable_swap_info(p, prio, swap_map);

	spin_unlock(&p->lock);

	spin_unlock(&swap_lock);

}
@@ -1554,7 +1552,7 @@ static void reinsert_swap_info(struct swap_info_struct *p) 
{

	spin_lock(&swap_lock);

	spin_lock(&p->lock);

	_enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));

	_enable_swap_info(p, p->prio, p->swap_map);

	spin_unlock(&p->lock);

	spin_unlock(&swap_lock);

}
@@ -1563,6 +1561,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) 
{

	struct swap_info_struct *p = NULL;

	unsigned char *swap_map;

	unsigned long *frontswap_map;

	struct file *swap_file, *victim;

	struct address_space *mapping;

	struct inode *inode;
@@ -1662,12 +1661,14 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) 
	swap_map = p->swap_map;

	p->swap_map = NULL;

	p->flags = 0;

	frontswap_invalidate_area(type);

	frontswap_map = frontswap_map_get(p);

	frontswap_map_set(p, NULL);

	spin_unlock(&p->lock);

	spin_unlock(&swap_lock);

	frontswap_invalidate_area(type);

	mutex_unlock(&swapon_mutex);

	vfree(swap_map);

	vfree(frontswap_map_get(p));

	vfree(frontswap_map);

	/* Destroy swap account informatin */

	swap_cgroup_swapoff(type);

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