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Date: Mon, 09 Jul 2012 14:02:10 -0700
From: Greg Thelen <gthelen@...gle.com>
To: Sha Zhengju <handai.szj@...il.com>
Cc: linux-mm@...ck.org, cgroups@...r.kernel.org,
kamezawa.hiroyu@...fujitsu.com, yinghan@...gle.com,
akpm@...ux-foundation.org, mhocko@...e.cz,
linux-kernel@...r.kernel.org, Sha Zhengju <handai.szj@...bao.com>
Subject: Re: [PATCH 5/7] memcg: add per cgroup dirty pages accounting
On Thu, Jun 28 2012, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@...bao.com>
>
> 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@...bao.com>
> ---
> 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.
> +
> 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()?
> 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.
> __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.
> 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;
> }
> - 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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