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authorHugh Dickins <hugh.dickins@tiscali.co.uk>2009-12-14 17:58:47 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-15 08:53:16 -0800
commitaaa468653b4a0d11c603c48d716f765177a5a9e4 (patch)
tree3cb8c9232dd405001fa38d5519937c5e6c6f32ab /mm
parent570a335b8e22579e2a51a68136d2b1f907a20eec (diff)
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: Hugh Dickins <hugh.dickins@tiscali.co.uk> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/shmem.c11
-rw-r--r--mm/swapfile.c47
2 files changed, 36 insertions, 22 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 356dd99566e..4fb41c83dac 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -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);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index cc5e7ebf2d2..58bec660016 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -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);
@@ -2127,6 +2125,15 @@ bad_file:
}
/*
+ * 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.
*/
int swap_duplicate(swp_entry_t entry)