On 07/10/2012 05:02 AM, Greg Thelen wrote:
On Thu, Jun 28 2012, Sha Zhengju wrote:
From: Sha Zhengju<handai.szj@xxxxxxxxxx>
This patch adds memcg routines to count dirty pages, which allows memory controller
to maintain an accurate view of the amount of its dirty memory and can provide some
info for users while group's direct reclaim is working.
After Kame's commit 89c06bd5(memcg: use new logic for page stat accounting), we can
use 'struct page' flag to test page state instead of per page_cgroup flag. But memcg
has a feature to move a page from a cgroup to another one and may have race between
"move" and "page stat accounting". So in order to avoid the race we have designed a
bigger lock:
mem_cgroup_begin_update_page_stat()
modify page information -->(a)
mem_cgroup_update_page_stat() -->(b)
mem_cgroup_end_update_page_stat()
It requires (a) and (b)(dirty pages accounting) can stay close enough.
In the previous two prepare patches, we have reworked the vfs set page dirty routines
and now the interfaces are more explicit:
incrementing (2):
__set_page_dirty
__set_page_dirty_nobuffers
decrementing (2):
clear_page_dirty_for_io
cancel_dirty_page
Signed-off-by: Sha Zhengju<handai.szj@xxxxxxxxxx>
---
fs/buffer.c | 17 ++++++++++++++---
include/linux/memcontrol.h | 1 +
mm/filemap.c | 5 +++++
mm/memcontrol.c | 28 +++++++++++++++++++++-------
mm/page-writeback.c | 30 ++++++++++++++++++++++++------
mm/truncate.c | 6 ++++++
6 files changed, 71 insertions(+), 16 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 55522dd..d3714cc 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -613,11 +613,19 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
int __set_page_dirty(struct page *page,
struct address_space *mapping, int warn)
{
+ bool locked;
+ unsigned long flags;
+ int ret = 0;
'= 0' and 'ret = 0' change (below) are redundant. My vote is to remove
'= 0' here.
Nice catch. :-)
+
if (unlikely(!mapping))
return !TestSetPageDirty(page);
- if (TestSetPageDirty(page))
- return 0;
+ mem_cgroup_begin_update_page_stat(page,&locked,&flags);
+
+ if (TestSetPageDirty(page)) {
+ ret = 0;
+ goto out;
+ }
spin_lock_irq(&mapping->tree_lock);
if (page->mapping) { /* Race with truncate? */
@@ -629,7 +637,10 @@ int __set_page_dirty(struct page *page,
spin_unlock_irq(&mapping->tree_lock);
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
- return 1;
+ ret = 1;
+out:
+ mem_cgroup_end_update_page_stat(page,&locked,&flags);
+ return ret;
}
/*
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 20b0f2d..ad37b59 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -38,6 +38,7 @@ enum mem_cgroup_stat_index {
MEM_CGROUP_STAT_RSS, /* # of pages charged as anon rss */
MEM_CGROUP_STAT_FILE_MAPPED, /* # of pages charged as file rss */
MEM_CGROUP_STAT_SWAP, /* # of pages, swapped out */
+ MEM_CGROUP_STAT_FILE_DIRTY, /* # of dirty pages in page cache */
MEM_CGROUP_STAT_NSTATS,
};
diff --git a/mm/filemap.c b/mm/filemap.c
index 1f19ec3..5159a49 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -140,6 +140,11 @@ void __delete_from_page_cache(struct page *page)
* having removed the page entirely.
*/
if (PageDirty(page)&& mapping_cap_account_dirty(mapping)) {
+ /*
+ * Do not change page state, so no need to use mem_cgroup_
+ * {begin, end}_update_page_stat to get lock.
+ */
+ mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
I do not understand this comment. What serializes this function and
mem_cgroup_move_account()?
The race is exist just because the two competitors share one
public variable and one reads it and the other writes it.
I thought if both sides(accounting and cgroup_move) do not
change page flag, then risks like doule-counting(see below)
will not happen.
CPU-A CPU-B
Set PG_dirty
(delay) move_lock_mem_cgroup()
if (PageDirty(page))
new_memcg->nr_dirty++
pc->mem_cgroup =
new_memcg;
move_unlock_mem_cgroup()
move_lock_mem_cgroup()
memcg = pc->mem_cgroup
new_memcg->nr_dirty++
But after second thoughts, it does have problem if without lock:
CPU-A CPU-B
if (PageDirty(page)) {
move_lock_mem_cgroup()
TestClearPageDirty(page))
memcg =
pc->mem_cgroup
new_memcg->nr_dirty --
move_unlock_mem_cgroup()
memcg = pc->mem_cgroup
new_memcg->nr_dirty--
}
It may occur race between clear_page_dirty() operation.
So this time I think we need the lock again...
Kame, what about your opinion...
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ebed1ca..90e2946 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -82,6 +82,7 @@ static const char * const mem_cgroup_stat_names[] = {
"rss",
"mapped_file",
"swap",
+ "dirty",
};
enum mem_cgroup_events_index {
@@ -2538,6 +2539,18 @@ void mem_cgroup_split_huge_fixup(struct page *head)
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+static inline
+void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
+ struct mem_cgroup *to,
+ enum mem_cgroup_stat_index idx)
+{
+ /* Update stat data for mem_cgroup */
+ preempt_disable();
+ __this_cpu_dec(from->stat->count[idx]);
+ __this_cpu_inc(to->stat->count[idx]);
+ preempt_enable();
+}
+
/**
* mem_cgroup_move_account - move account of the page
* @page: the page
@@ -2583,13 +2596,14 @@ static int mem_cgroup_move_account(struct page *page,
move_lock_mem_cgroup(from,&flags);
- if (!anon&& page_mapped(page)) {
- /* Update mapped_file data for mem_cgroup */
- preempt_disable();
- __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
- __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
- preempt_enable();
- }
+ if (!anon&& page_mapped(page))
+ mem_cgroup_move_account_page_stat(from, to,
+ MEM_CGROUP_STAT_FILE_MAPPED);
+
+ if (PageDirty(page))
+ mem_cgroup_move_account_page_stat(from, to,
+ MEM_CGROUP_STAT_FILE_DIRTY);
+
mem_cgroup_charge_statistics(from, anon, -nr_pages);
/* caller should have done css_get */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e5363f3..e79a2f7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1962,6 +1962,7 @@ int __set_page_dirty_no_writeback(struct page *page)
void account_page_dirtied(struct page *page, struct address_space *mapping)
{
if (mapping_cap_account_dirty(mapping)) {
+ mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
It might be helpful to add a comment to account_page_dirtied()
indicating that caller must hold mem_cgroup_begin_update_page_stat()
lock. Extra credit for an new assertion added to
mem_cgroup_update_page_stat() confirming the needed lock is held.
Got it! :-)
__inc_zone_page_state(page, NR_FILE_DIRTY);
__inc_zone_page_state(page, NR_DIRTIED);
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
@@ -2001,12 +2002,20 @@ EXPORT_SYMBOL(account_page_writeback);
*/
int __set_page_dirty_nobuffers(struct page *page)
{
+ bool locked;
+ unsigned long flags;
+ int ret = 0;
+
+ mem_cgroup_begin_update_page_stat(page,&locked,&flags);
+
Is there a strict lock ordering which says that
mem_cgroup_begin_update_page_stat() must not be called while holding
tree_lock? If yes, then maybe we should update the 'Lock ordering'
comment in mm/filemap.c to describe the
mem_cgroup_begin_update_page_stat() lock.
I think yes, otherwise it may cause deadlock. I'll update it later.
if (!TestSetPageDirty(page)) {
struct address_space *mapping = page_mapping(page);
struct address_space *mapping2;
- if (!mapping)
- return 1;
+ if (!mapping) {
+ ret = 1;
+ goto out;
+ }
The following seems even easier because it does not need your 'ret = 1'
change below.
+ ret = 1;
if (!mapping)
- return 1;
+ goto out;
spin_lock_irq(&mapping->tree_lock);
mapping2 = page_mapping(page);
@@ -2022,9 +2031,12 @@ int __set_page_dirty_nobuffers(struct page *page)
/* !PageAnon&& !swapper_space */
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
}
- return 1;
+ ret = 1;
With the ret=1 change above, this can be changed to:
- return 1;
Seems better.
}
- return 0;
+
+out:
+ mem_cgroup_end_update_page_stat(page,&locked,&flags);
+ return ret;
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
@@ -2139,6 +2151,9 @@ EXPORT_SYMBOL(set_page_dirty_lock);
int clear_page_dirty_for_io(struct page *page)
{
struct address_space *mapping = page_mapping(page);
+ bool locked;
+ unsigned long flags;
+ int ret = 0;
BUG_ON(!PageLocked(page));
@@ -2180,13 +2195,16 @@ int clear_page_dirty_for_io(struct page *page)
* the desired exclusion. See mm/memory.c:do_wp_page()
* for more comments.
*/
+ mem_cgroup_begin_update_page_stat(page,&locked,&flags);
if (TestClearPageDirty(page)) {
+ mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
- return 1;
+ ret = 1;
}
- return 0;
+ mem_cgroup_end_update_page_stat(page,&locked,&flags);
+ return ret;
}
return TestClearPageDirty(page);
}
diff --git a/mm/truncate.c b/mm/truncate.c
index 75801ac..052016a 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -73,9 +73,14 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
*/
void cancel_dirty_page(struct page *page, unsigned int account_size)
{
+ bool locked;
+ unsigned long flags;
+
+ mem_cgroup_begin_update_page_stat(page,&locked,&flags);
if (TestClearPageDirty(page)) {
struct address_space *mapping = page->mapping;
if (mapping&& mapping_cap_account_dirty(mapping)) {
+ mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
@@ -83,6 +88,7 @@ void cancel_dirty_page(struct page *page, unsigned int account_size)
task_io_account_cancelled_write(account_size);
}
}
+ mem_cgroup_end_update_page_stat(page,&locked,&flags);
}
EXPORT_SYMBOL(cancel_dirty_page);
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