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Commit aaa46865 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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swap_info: note SWAP_MAP_SHMEM 



While we're fiddling with the swap_map values, let's assign a particular
value to shmem/tmpfs swap pages: their swap counts are never incremented,
and it helps swapoff's try_to_unuse() a little if it can immediately
distinguish those pages from process pages.

Since we've no use for SWAP_MAP_BAD | COUNT_CONTINUED,
we might as well use that 0xbf value for SWAP_MAP_SHMEM.

Signed-off-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 570a335b

include/linux/swap.h

+6 −0
Original line number Diff line number Diff line
@@ -157,6 +157,7 @@ enum { 
#define SWAP_HAS_CACHE	0x40	/* Flag page is cached, in first swap_map */

#define SWAP_CONT_MAX	0x7f	/* Max count, in each swap_map continuation */

#define COUNT_CONTINUED	0x80	/* See swap_map continuation for full count */

#define SWAP_MAP_SHMEM	0xbf	/* Owned by shmem/tmpfs, in first swap_map */



/*

 * The in-memory structure used to track swap areas.
@@ -316,6 +317,7 @@ extern swp_entry_t get_swap_page(void); 
extern swp_entry_t get_swap_page_of_type(int);

extern int valid_swaphandles(swp_entry_t, unsigned long *);

extern int add_swap_count_continuation(swp_entry_t, gfp_t);

extern void swap_shmem_alloc(swp_entry_t);

extern int swap_duplicate(swp_entry_t);

extern int swapcache_prepare(swp_entry_t);

extern void swap_free(swp_entry_t);
@@ -394,6 +396,10 @@ static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask) 
	return 0;

}



static inline void swap_shmem_alloc(swp_entry_t swp)

{

}



static inline int swap_duplicate(swp_entry_t swp)

{

	return 0;

mm/shmem.c

+9 −2
Original line number Diff line number Diff line
@@ -1017,7 +1017,14 @@ int shmem_unuse(swp_entry_t entry, struct page *page) 
			goto out;

	}

	mutex_unlock(&shmem_swaplist_mutex);

out:	return found;	/* 0 or 1 or -ENOMEM */

	/*

	 * Can some race bring us here?  We've been holding page lock,

	 * so I think not; but would rather try again later than BUG()

	 */

	unlock_page(page);

	page_cache_release(page);

out:

	return (found < 0) ? found : 0;

}



/*
@@ -1080,7 +1087,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) 
		else

			inode = NULL;

		spin_unlock(&info->lock);

		swap_duplicate(swap);

		swap_shmem_alloc(swap);

		BUG_ON(page_mapped(page));

		page_cache_release(page);	/* pagecache ref */

		swap_writepage(page, wbc);

mm/swapfile.c

+27 −20
Original line number Diff line number Diff line
@@ -548,6 +548,12 @@ static unsigned char swap_entry_free(struct swap_info_struct *p, 
	if (usage == SWAP_HAS_CACHE) {

		VM_BUG_ON(!has_cache);

		has_cache = 0;

	} else if (count == SWAP_MAP_SHMEM) {

		/*

		 * Or we could insist on shmem.c using a special

		 * swap_shmem_free() and free_shmem_swap_and_cache()...

		 */

		count = 0;

	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {

		if (count == COUNT_CONTINUED) {

			if (swap_count_continued(p, offset, count))
@@ -1031,7 +1037,6 @@ static int try_to_unuse(unsigned int type) 
	swp_entry_t entry;

	unsigned int i = 0;

	int retval = 0;

	int shmem;



	/*

	 * When searching mms for an entry, a good strategy is to
@@ -1107,17 +1112,18 @@ static int try_to_unuse(unsigned int type) 


		/*

		 * 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 (swap_count(swcount)) {

			if (start_mm == &init_mm)

				shmem = shmem_unuse(entry, page);

			else

				retval = unuse_mm(start_mm, entry, page);

		if (swap_count(swcount) == SWAP_MAP_SHMEM) {

			retval = shmem_unuse(entry, page);

			/* page has already been unlocked and released */

			if (retval < 0)

				break;

			continue;

		}

		if (swap_count(swcount) && start_mm != &init_mm)

			retval = unuse_mm(start_mm, entry, page);



		if (swap_count(*swap_map)) {

			int set_start_mm = (*swap_map >= swcount);

			struct list_head *p = &start_mm->mmlist;
@@ -1128,7 +1134,7 @@ static int try_to_unuse(unsigned int type) 
			atomic_inc(&new_start_mm->mm_users);

			atomic_inc(&prev_mm->mm_users);

			spin_lock(&mmlist_lock);

			while (swap_count(*swap_map) && !retval && !shmem &&

			while (swap_count(*swap_map) && !retval &&

					(p = p->next) != &start_mm->mmlist) {

				mm = list_entry(p, struct mm_struct, mmlist);

				if (!atomic_inc_not_zero(&mm->mm_users))
@@ -1142,10 +1148,9 @@ static int try_to_unuse(unsigned int type) 
				swcount = *swap_map;

				if (!swap_count(swcount)) /* any usage ? */

					;

				else if (mm == &init_mm) {

				else if (mm == &init_mm)

					set_start_mm = 1;

					shmem = shmem_unuse(entry, page);

				} else

				else

					retval = unuse_mm(mm, entry, page);



				if (set_start_mm && *swap_map < swcount) {
@@ -1161,13 +1166,6 @@ static int try_to_unuse(unsigned int type) 
			mmput(start_mm);

			start_mm = new_start_mm;

		}

		if (shmem) {

			/* page has already been unlocked and released */

			if (shmem > 0)

				continue;

			retval = shmem;

			break;

		}

		if (retval) {

			unlock_page(page);

			page_cache_release(page);
@@ -2126,6 +2124,15 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage) 
	goto out;

}



/*

 * Help swapoff by noting that swap entry belongs to shmem/tmpfs

 * (in which case its reference count is never incremented).

 */

void swap_shmem_alloc(swp_entry_t entry)

{

	__swap_duplicate(entry, SWAP_MAP_SHMEM);

}



/*

 * increase reference count of swap entry by 1.

 */