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Date: Mon, 27 Jan 2014 18:03:04 +0800
From: Weijie Yang <weijie.yang@...sung.com>
To: hughd@...gle.com, 'Seth Jennings' <sjennings@...iantweb.net>
Cc: 'Andrew Morton' <akpm@...ux-foundation.org>,
'Minchan Kim' <minchan@...nel.org>, shli@...nel.org,
'Bob Liu' <bob.liu@...cle.com>, weijie.yang.kh@...il.com,
'Heesub Shin' <heesub.shin@...sung.com>, mquzik@...hat.com,
'Linux-MM' <linux-mm@...ck.org>,
'linux-kernel' <linux-kernel@...r.kernel.org>,
stable@...r.kernel.org
Subject: [PATCH 5/8] mm/swap: drop useless and bug frontswap_shrink codes
The frontswap_shrink works as a "partial swapoff" by using try_to_unuse(),
but is has race condition with swapoff.
Of course we can fix this race issue, however, as this code is not used by
anyone and not efficient, I decide drop this code.
As to shrinker, a frontswap backend should implement its own shrinker if
there is a real-world need.
Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
---
include/linux/frontswap.h | 2 -
include/linux/swapfile.h | 3 --
mm/frontswap.c | 116 ---------------------------------------------
mm/swapfile.c | 19 ++------
4 files changed, 4 insertions(+), 136 deletions(-)
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 8293262..c00b429 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -16,8 +16,6 @@ struct frontswap_ops {
extern bool frontswap_enabled;
extern struct frontswap_ops *
frontswap_register_ops(struct frontswap_ops *ops);
-extern void frontswap_shrink(unsigned long);
-extern unsigned long frontswap_curr_pages(void);
extern void frontswap_writethrough(bool);
#define FRONTSWAP_HAS_EXCLUSIVE_GETS
extern void frontswap_tmem_exclusive_gets(bool);
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index 1fd5494..5dc7c81 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -5,10 +5,7 @@
* these were static in swapfile.c but frontswap.c needs them and we don't
* want to expose them to the dozens of source files that include swap.h
*/
-extern spinlock_t swap_lock;
extern struct mutex swapon_mutex;
-extern struct swap_list_t swap_list;
extern struct swap_info_struct *swap_info[];
-extern int try_to_unuse(unsigned int, bool, unsigned long);
#endif /* _LINUX_SWAPFILE_H */
diff --git a/mm/frontswap.c b/mm/frontswap.c
index a0c68db..df067f1 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -326,122 +326,6 @@ void __frontswap_invalidate_area(unsigned type)
}
EXPORT_SYMBOL(__frontswap_invalidate_area);
-static unsigned long __frontswap_curr_pages(void)
-{
- int type;
- unsigned long totalpages = 0;
- struct swap_info_struct *si = NULL;
-
- assert_spin_locked(&swap_lock);
- for (type = swap_list.head; type >= 0; type = si->next) {
- si = swap_info[type];
- totalpages += atomic_read(&si->frontswap_pages);
- }
- return totalpages;
-}
-
-static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
- int *swapid)
-{
- int ret = -EINVAL;
- struct swap_info_struct *si = NULL;
- int si_frontswap_pages;
- unsigned long total_pages_to_unuse = total;
- unsigned long pages = 0, pages_to_unuse = 0;
- int type;
-
- assert_spin_locked(&swap_lock);
- for (type = swap_list.head; type >= 0; type = si->next) {
- si = swap_info[type];
- si_frontswap_pages = atomic_read(&si->frontswap_pages);
- if (total_pages_to_unuse < si_frontswap_pages) {
- pages = pages_to_unuse = total_pages_to_unuse;
- } else {
- pages = si_frontswap_pages;
- pages_to_unuse = 0; /* unuse all */
- }
- /* ensure there is enough RAM to fetch pages from frontswap */
- if (security_vm_enough_memory_mm(current->mm, pages)) {
- ret = -ENOMEM;
- continue;
- }
- vm_unacct_memory(pages);
- *unused = pages_to_unuse;
- *swapid = type;
- ret = 0;
- break;
- }
-
- return ret;
-}
-
-/*
- * Used to check if it's necessory and feasible to unuse pages.
- * Return 1 when nothing to do, 0 when need to shink pages,
- * error code when there is an error.
- */
-static int __frontswap_shrink(unsigned long target_pages,
- unsigned long *pages_to_unuse,
- int *type)
-{
- unsigned long total_pages = 0, total_pages_to_unuse;
-
- assert_spin_locked(&swap_lock);
-
- total_pages = __frontswap_curr_pages();
- if (total_pages <= target_pages) {
- /* Nothing to do */
- *pages_to_unuse = 0;
- return 1;
- }
- total_pages_to_unuse = total_pages - target_pages;
- return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
-}
-
-/*
- * Frontswap, like a true swap device, may unnecessarily retain pages
- * under certain circumstances; "shrink" frontswap is essentially a
- * "partial swapoff" and works by calling try_to_unuse to attempt to
- * unuse enough frontswap pages to attempt to -- subject to memory
- * constraints -- reduce the number of pages in frontswap to the
- * number given in the parameter target_pages.
- */
-void frontswap_shrink(unsigned long target_pages)
-{
- unsigned long pages_to_unuse = 0;
- int uninitialized_var(type), ret;
-
- /*
- * we don't want to hold swap_lock while doing a very
- * lengthy try_to_unuse, but swap_list may change
- * so restart scan from swap_list.head each time
- */
- spin_lock(&swap_lock);
- ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
- spin_unlock(&swap_lock);
- if (ret == 0)
- try_to_unuse(type, true, pages_to_unuse);
- return;
-}
-EXPORT_SYMBOL(frontswap_shrink);
-
-/*
- * Count and return the number of frontswap pages across all
- * swap devices. This is exported so that backend drivers can
- * determine current usage without reading debugfs.
- */
-unsigned long frontswap_curr_pages(void)
-{
- unsigned long totalpages = 0;
-
- spin_lock(&swap_lock);
- totalpages = __frontswap_curr_pages();
- spin_unlock(&swap_lock);
-
- return totalpages;
-}
-EXPORT_SYMBOL(frontswap_curr_pages);
-
static int __init init_frontswap(void)
{
#ifdef CONFIG_DEBUG_FS
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5c8a086..3023172 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1353,7 +1353,7 @@ static int unuse_mm(struct mm_struct *mm,
* Recycle to start on reaching the end, returning 0 when empty.
*/
static unsigned int find_next_to_unuse(struct swap_info_struct *si,
- unsigned int prev, bool frontswap)
+ unsigned int prev)
{
unsigned int max = si->max;
unsigned int i = prev;
@@ -1379,12 +1379,6 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
prev = 0;
i = 1;
}
- if (frontswap) {
- if (frontswap_test(si, i))
- break;
- else
- continue;
- }
count = ACCESS_ONCE(si->swap_map[i]);
if (count && swap_count(count) != SWAP_MAP_BAD)
break;
@@ -1400,8 +1394,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
* if the boolean frontswap is true, only unuse pages_to_unuse pages;
* pages_to_unuse==0 means all pages; ignored if frontswap is false
*/
-int try_to_unuse(unsigned int type, bool frontswap,
- unsigned long pages_to_unuse)
+int try_to_unuse(unsigned int type)
{
struct swap_info_struct *si = swap_info[type];
struct mm_struct *start_mm;
@@ -1438,7 +1431,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
* 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, frontswap)) != 0) {
+ while ((i = find_next_to_unuse(si, i)) != 0) {
if (signal_pending(current)) {
retval = -EINTR;
break;
@@ -1613,10 +1606,6 @@ int try_to_unuse(unsigned int type, bool frontswap,
* interactive performance.
*/
cond_resched();
- if (frontswap && pages_to_unuse > 0) {
- if (!--pages_to_unuse)
- break;
- }
}
mmput(start_mm);
@@ -1939,7 +1928,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
spin_unlock(&swap_lock);
set_current_oom_origin();
- err = try_to_unuse(type, false, 0); /* force all pages to be unused */
+ err = try_to_unuse(type); /* force all pages to be unused */
clear_current_oom_origin();
if (err) {
--
1.7.10.4
--
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