From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: page-writeback: simplify memcg handling in test_clear_page_writeback()
Page writeback doesn't hold a page reference, which allows truncate to
free a page the second PageWriteback is cleared. This used to require
special attention in test_clear_page_writeback(), where we had to be
careful not to rely on the unstable page->memcg binding and look up all
the necessary information before clearing the writeback flag.
Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and
BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an
explicit reference on the page, and this dance is no longer needed.
Use unlock_page_memcg() and dec_lruvec_page_state() directly.
This removes the last user of the lock_page_memcg() return value, change
it to void. Touch up the comments in there as well. This also removes
the last extern user of __unlock_page_memcg(), make it static. Further,
it removes the last user of dec_lruvec_state(), delete it, along with a
few other unused helpers.
Link: https://lkml.kernel.org/r/YCQbYAWg4nvBFL6h@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 10 +--------
include/linux/vmstat.h | 24 ++---------------------
mm/memcontrol.c | 36 ++++++++++-------------------------
mm/page-writeback.c | 9 ++------
4 files changed, 19 insertions(+), 60 deletions(-)
--- a/include/linux/memcontrol.h~mm-page-writeback-simplify-memcg-handling-in-test_clear_page_writeback
+++ a/include/linux/memcontrol.h
@@ -867,8 +867,7 @@ void mem_cgroup_print_oom_group(struct m
extern bool cgroup_memory_noswap;
#endif
-struct mem_cgroup *lock_page_memcg(struct page *page);
-void __unlock_page_memcg(struct mem_cgroup *memcg);
+void lock_page_memcg(struct page *page);
void unlock_page_memcg(struct page *page);
/*
@@ -1289,12 +1288,7 @@ mem_cgroup_print_oom_meminfo(struct mem_
{
}
-static inline struct mem_cgroup *lock_page_memcg(struct page *page)
-{
- return NULL;
-}
-
-static inline void __unlock_page_memcg(struct mem_cgroup *memcg)
+static inline void lock_page_memcg(struct page *page)
{
}
--- a/include/linux/vmstat.h~mm-page-writeback-simplify-memcg-handling-in-test_clear_page_writeback
+++ a/include/linux/vmstat.h
@@ -512,16 +512,10 @@ static inline void mod_lruvec_page_state
#endif /* CONFIG_MEMCG */
-static inline void __inc_lruvec_state(struct lruvec *lruvec,
- enum node_stat_item idx)
-{
- __mod_lruvec_state(lruvec, idx, 1);
-}
-
-static inline void __dec_lruvec_state(struct lruvec *lruvec,
- enum node_stat_item idx)
+static inline void inc_lruvec_state(struct lruvec *lruvec,
+ enum node_stat_item idx)
{
- __mod_lruvec_state(lruvec, idx, -1);
+ mod_lruvec_state(lruvec, idx, 1);
}
static inline void __inc_lruvec_page_state(struct page *page,
@@ -536,18 +530,6 @@ static inline void __dec_lruvec_page_sta
__mod_lruvec_page_state(page, idx, -1);
}
-static inline void inc_lruvec_state(struct lruvec *lruvec,
- enum node_stat_item idx)
-{
- mod_lruvec_state(lruvec, idx, 1);
-}
-
-static inline void dec_lruvec_state(struct lruvec *lruvec,
- enum node_stat_item idx)
-{
- mod_lruvec_state(lruvec, idx, -1);
-}
-
static inline void inc_lruvec_page_state(struct page *page,
enum node_stat_item idx)
{
--- a/mm/memcontrol.c~mm-page-writeback-simplify-memcg-handling-in-test_clear_page_writeback
+++ a/mm/memcontrol.c
@@ -2118,11 +2118,10 @@ void mem_cgroup_print_oom_group(struct m
* This function protects unlocked LRU pages from being moved to
* another cgroup.
*
- * It ensures lifetime of the returned memcg. Caller is responsible
- * for the lifetime of the page; __unlock_page_memcg() is available
- * when @page might get freed inside the locked section.
+ * It ensures lifetime of the locked memcg. Caller is responsible
+ * for the lifetime of the page.
*/
-struct mem_cgroup *lock_page_memcg(struct page *page)
+void lock_page_memcg(struct page *page)
{
struct page *head = compound_head(page); /* rmap on tail pages */
struct mem_cgroup *memcg;
@@ -2132,21 +2131,15 @@ struct mem_cgroup *lock_page_memcg(struc
* The RCU lock is held throughout the transaction. The fast
* path can get away without acquiring the memcg->move_lock
* because page moving starts with an RCU grace period.
- *
- * The RCU lock also protects the memcg from being freed when
- * the page state that is going to change is the only thing
- * preventing the page itself from being freed. E.g. writeback
- * doesn't hold a page reference and relies on PG_writeback to
- * keep off truncation, migration and so forth.
*/
rcu_read_lock();
if (mem_cgroup_disabled())
- return NULL;
+ return;
again:
memcg = page_memcg(head);
if (unlikely(!memcg))
- return NULL;
+ return;
#ifdef CONFIG_PROVE_LOCKING
local_irq_save(flags);
@@ -2155,7 +2148,7 @@ again:
#endif
if (atomic_read(&memcg->moving_account) <= 0)
- return memcg;
+ return;
spin_lock_irqsave(&memcg->move_lock, flags);
if (memcg != page_memcg(head)) {
@@ -2164,24 +2157,17 @@ again:
}
/*
- * When charge migration first begins, we can have locked and
- * unlocked page stat updates happening concurrently. Track
- * the task who has the lock for unlock_page_memcg().
+ * When charge migration first begins, we can have multiple
+ * critical sections holding the fast-path RCU lock and one
+ * holding the slowpath move_lock. Track the task who has the
+ * move_lock for unlock_page_memcg().
*/
memcg->move_lock_task = current;
memcg->move_lock_flags = flags;
-
- return memcg;
}
EXPORT_SYMBOL(lock_page_memcg);
-/**
- * __unlock_page_memcg - unlock and unpin a memcg
- * @memcg: the memcg
- *
- * Unlock and unpin a memcg returned by lock_page_memcg().
- */
-void __unlock_page_memcg(struct mem_cgroup *memcg)
+static void __unlock_page_memcg(struct mem_cgroup *memcg)
{
if (memcg && memcg->move_lock_task == current) {
unsigned long flags = memcg->move_lock_flags;
--- a/mm/page-writeback.c~mm-page-writeback-simplify-memcg-handling-in-test_clear_page_writeback
+++ a/mm/page-writeback.c
@@ -2722,12 +2722,9 @@ EXPORT_SYMBOL(clear_page_dirty_for_io);
int test_clear_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
- struct mem_cgroup *memcg;
- struct lruvec *lruvec;
int ret;
- memcg = lock_page_memcg(page);
- lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
+ lock_page_memcg(page);
if (mapping && mapping_use_writeback_tags(mapping)) {
struct inode *inode = mapping->host;
struct backing_dev_info *bdi = inode_to_bdi(inode);
@@ -2755,11 +2752,11 @@ int test_clear_page_writeback(struct pag
ret = TestClearPageWriteback(page);
}
if (ret) {
- dec_lruvec_state(lruvec, NR_WRITEBACK);
+ dec_lruvec_page_state(page, NR_WRITEBACK);
dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
inc_node_page_state(page, NR_WRITTEN);
}
- __unlock_page_memcg(memcg);
+ unlock_page_memcg(page);
return ret;
}
_
