From: Jamie Liu <jamie...@google.com>
swap_list is used by get_swap_page() to find public swap files to swap
to; in the case that there are many private swap files and few public
swap files, get_swap_page() may waste time iterating through private
swap files it can't swap to. Change _enable_swap_info() to not insert
private swap files onto swap_list; this improves the performance of
get_swap_page() in such cases, at the cost of making
swap_store_swap_device() and swapoff() minutely slower (both of which
are non-critical).
Signed-off-by: Jamie Liu <jamie...@google.com>
Signed-off-by: Yu Zhao <yuz...@google.com>
---
mm/swapfile.c | 84 +++++++++++++++++++++++++++++++++--------------------------
1 file changed, 47 insertions(+), 37 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 18a8eee..27e147b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -712,14 +712,14 @@ int swap_store_swap_device(const char *buf, int *_type)
mapping = victim->f_mapping;
spin_lock(&swap_lock);
- for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
+ for (type = 0; type < nr_swapfiles; type++) {
si = swap_info[type];
if ((si->flags & SWP_WRITEOK) == SWP_WRITEOK) {
if (si->swap_file->f_mapping == mapping)
break;
}
}
- if (type < 0) {
+ if (type == nr_swapfiles) {
err = -EINVAL;
} else {
err = 0;
@@ -803,10 +803,7 @@ swp_entry_t get_swap_page(struct page *page)
spin_unlock(&si->lock);
continue;
}
- if (si->flags & SWP_PRIVATE) {
- spin_unlock(&si->lock);
- continue;
- }
+ BUG_ON(si->flags & SWP_PRIVATE);
swap_list.next = next;
@@ -957,11 +954,12 @@ static unsigned char swap_entry_free(struct
swap_info_struct *p,
p->lowest_bit = offset;
if (offset > p->highest_bit)
p->highest_bit = offset;
- set_highest_priority_index(p->type);
if (p->flags & SWP_PRIVATE)
atomic_long_inc(&nr_private_swap_pages);
- else
+ else {
atomic_long_inc(&nr_public_swap_pages);
+ set_highest_priority_index(p->type);
+ }
p->inuse_pages--;
frontswap_invalidate_page(p->type, offset);
if (p->flags & SWP_BLKDEV) {
@@ -1899,6 +1897,8 @@ static void _enable_swap_info(struct swap_info_struct *p,
int prio,
if (prio >= 0)
p->prio = prio;
+ else if (p->flags & SWP_PRIVATE)
+ p->prio = 0;
else
p->prio = --least_priority;
p->swap_map = swap_map;
@@ -1910,19 +1910,19 @@ static void _enable_swap_info(struct swap_info_struct
*p, int prio,
} else {
atomic_long_add(p->pages, &nr_public_swap_pages);
total_public_swap_pages += p->pages;
+ /* insert swap space into swap_list: */
+ prev = -1;
+ for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+ if (p->prio >= swap_info[i]->prio)
+ break;
+ prev = i;
+ }
+ p->next = i;
+ if (prev < 0)
+ swap_list.head = swap_list.next = p->type;
+ else
+ swap_info[prev]->next = p->type;
}
- /* insert swap space into swap_list: */
- prev = -1;
- for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
- if (p->prio >= swap_info[i]->prio)
- break;
- prev = i;
- }
- p->next = i;
- if (prev < 0)
- swap_list.head = swap_list.next = p->type;
- else
- swap_info[prev]->next = p->type;
}
static void enable_swap_info(struct swap_info_struct *p, int prio,
@@ -1978,15 +1978,25 @@ SYSCALL_DEFINE1(swapoff, const char __user *,
specialfile)
mapping = victim->f_mapping;
prev = -1;
spin_lock(&swap_lock);
- for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
+ for (type = 0; type < nr_swapfiles; type++) {
p = swap_info[type];
if (p->flags & SWP_WRITEOK) {
- if (p->swap_file->f_mapping == mapping)
+ if (p->swap_file->f_mapping == mapping) {
+ /* Private swapfiles aren't in swap_list */
+ if (p->flags & SWP_PRIVATE)
+ break;
+ /* Find type's predecessor in swap_list */
+ for (i = swap_list.head; i >= 0;
+ i = swap_info[i]->next) {
+ if (type == i)
+ break;
+ prev = i;
+ }
break;
+ }
}
- prev = type;
}
- if (type < 0) {
+ if (type == nr_swapfiles) {
err = -EINVAL;
spin_unlock(&swap_lock);
goto out_dput;
@@ -1998,24 +2008,24 @@ SYSCALL_DEFINE1(swapoff, const char __user *,
specialfile)
spin_unlock(&swap_lock);
goto out_dput;
}
- if (prev < 0)
- swap_list.head = p->next;
- else
- swap_info[prev]->next = p->next;
- if (type == swap_list.next) {
- /* just pick something that's safe... */
- swap_list.next = swap_list.head;
- }
spin_lock(&p->lock);
- if (p->prio < 0) {
- for (i = p->next; i >= 0; i = swap_info[i]->next)
- swap_info[i]->prio = p->prio--;
- least_priority++;
- }
if (p->flags & SWP_PRIVATE) {
atomic_long_sub(p->pages, &nr_private_swap_pages);
total_private_swap_pages -= p->pages;
} else {
+ if (prev < 0)
+ swap_list.head = p->next;
+ else
+ swap_info[prev]->next = p->next;
+ if (type == swap_list.next) {
+ /* just pick something that's safe... */
+ swap_list.next = swap_list.head;
+ }
+ if (p->prio < 0) {
+ for (i = p->next; i >= 0; i = swap_info[i]->next)
+ swap_info[i]->prio = p->prio--;
+ least_priority++;
+ }
atomic_long_sub(p->pages, &nr_public_swap_pages);
total_public_swap_pages -= p->pages;
}
--
1.9.1.423.g4596e3a
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