On Fri, 9 Mar 2012 15:01:09 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> On Fri, 9 Mar 2012 12:24:48 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > > I'd rather delete than add code here!
> > >
> >
> > As a user, for Fujitsu, I believe it's insane to move task between cgroups.
> > So, I have no benefit from this code, at all.
> > Ok, maybe I'm not a stakeholder,here.
> >
> I agree that moving tasks between cgroup is not a sane operation,
> users won't do it so frequently, but I cannot prevent that.
> That's why I implemented this feature.
>
> > If users say all shared pages should be moved, ok, let's move.
> > But change of behavior should be documented and implemented in an independet
> > patch. CC'ed Nishimura-san, he implemetned this, a real user.
> >
> To be honest, shared anon is not my concern. My concern is
> shared memory(that's why, mapcount is not checked as for file pages.
> I assume all processes sharing the same shared memory will be moved together).
> So, it's all right for me to change the behavior for shared anon(or leave
> it as it is).
>
Thank you for comment. Then, here is a patch.
Other opinions ?
==
>From 1012e97e3b123fb80d0ec6b1f5d3dbc87a5a5139 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Date: Fri, 9 Mar 2012 16:22:32 +0900
Subject: [PATCH] memcg: fix/change behavior of shared anon at moving task.
In documentation, it's said that 'shared anon are not moved'.
But in implementation, this check was done.
if (!move_anon() || page_mapcount(page) > 2)
Ah, memcg has been moving shared anon pages for a long time.
Then, here is a discussion about handling of shared anon pages.
- It's complex
- Now, shared file caches are moved in force.
- It adds unclear check as page_mapcount(). To do correct check,
we should check swap users, etc.
- No one notice this implementation behavior. So, no one get benefit
from the design.
- In general, once task is moved to a cgroup for running, it will not
be moved....
- Finally, we have control knob as memory.move_charge_at_immigrate.
Here is a patch to allow moving shared pages. This makes memcg simpler
and fix current broken implementation.
I added a notice for what happens at fork() -> move -> exec() usage.
Note:
IIUC, libcgroup's cgroup daemon moves tasks after exec().
So, it's not affected.
libcgroup's command "cgexec" does move itsef to a memcg and call exec()
without fork(). it's not affected.
Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
Documentation/cgroups/memory.txt | 10 ++++++++--
include/linux/swap.h | 9 ---------
mm/memcontrol.c | 15 +++------------
mm/swapfile.c | 31 -------------------------------
4 files changed, 11 insertions(+), 54 deletions(-)
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 4c95c00..16bc9f2 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -185,6 +185,9 @@ behind this approach is that a cgroup that aggressively uses a shared
page will eventually get charged for it (once it is uncharged from
the cgroup that brought it in -- this will happen on memory pressure).
+(*)See section 8.2. At task moving, you can recharge mapped pages to other
+ cgroup.
+
Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.
When you do swapoff and make swapped-out pages of shmem(tmpfs) to
be backed into memory in force, charges for pages are accounted against the
@@ -623,8 +626,8 @@ memory cgroup.
bit | what type of charges would be moved ?
-----+------------------------------------------------------------------------
0 | A charge of an anonymous page(or swap of it) used by the target task.
- | Those pages and swaps must be used only by the target task. You must
- | enable Swap Extension(see 2.4) to enable move of swap charges.
+ | Even if it's shared, it will be moved in force(*). You must enable Swap
+ | Extension(see 2.4) to enable move of swap charges.
-----+------------------------------------------------------------------------
1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory)
| and swaps of tmpfs file) mmapped by the target task. Unlike the case of
@@ -635,6 +638,9 @@ memory cgroup.
| page_mapcount(page) > 1). You must enable Swap Extension(see 2.4) to
| enable move of swap charges.
+(*) Because of this, fork() -> move -> exec() will move all parent's page
+ to the target cgroup. Please be careful.
+
8.3 TODO
- Implement madvise(2) to let users decide the vma to be moved or not to be
diff --git a/include/linux/swap.h b/include/linux/swap.h
index f7df3ea..13c8d6f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -390,7 +390,6 @@ static inline void deactivate_swap_token(struct mm_struct *mm, bool swap_token)
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
extern void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout);
-extern int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep);
#else
static inline void
mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
@@ -535,14 +534,6 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)
{
}
-#ifdef CONFIG_CGROUP_MEM_RES_CTLR
-static inline int
-mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
-{
- return 0;
-}
-#endif
-
#endif /* CONFIG_SWAP */
#endif /* __KERNEL__*/
#endif /* _LINUX_SWAP_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c83aeb5..e7e4e3d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5100,12 +5100,9 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
if (!page || !page_mapped(page))
return NULL;
- if (PageAnon(page)) {
- /* we don't move shared anon */
- if (!move_anon() || page_mapcount(page) > 2)
- return NULL;
+ if (PageAnon(page) && !move_anon()) {
+ return NULL;
} else if (!move_file())
- /* we ignore mapcount for file pages */
return NULL;
if (!get_page_unless_zero(page))
return NULL;
@@ -5116,18 +5113,12 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
- int usage_count;
struct page *page = NULL;
swp_entry_t ent = pte_to_swp_entry(ptent);
if (!move_anon() || non_swap_entry(ent))
return NULL;
- usage_count = mem_cgroup_count_swap_user(ent, &page);
- if (usage_count > 1) { /* we don't move shared anon */
- if (page)
- put_page(page);
- return NULL;
- }
+ page = lookup_swap_cache(ent);
if (do_swap_account)
entry->val = ent.val;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index fa3c519..85b4548 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -720,37 +720,6 @@ int free_swap_and_cache(swp_entry_t entry)
return p != NULL;
}
-#ifdef CONFIG_CGROUP_MEM_RES_CTLR
-/**
- * mem_cgroup_count_swap_user - count the user of a swap entry
- * @ent: the swap entry to be checked
- * @pagep: the pointer for the swap cache page of the entry to be stored
- *
- * Returns the number of the user of the swap entry. The number is valid only
- * for swaps of anonymous pages.
- * If the entry is found on swap cache, the page is stored to pagep with
- * refcount of it being incremented.
- */
-int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
-{
- struct page *page;
- struct swap_info_struct *p;
- int count = 0;
-
- page = find_get_page(&swapper_space, ent.val);
- if (page)
- count += page_mapcount(page);
- p = swap_info_get(ent);
- if (p) {
- count += swap_count(p->swap_map[swp_offset(ent)]);
- spin_unlock(&swap_lock);
- }
-
- *pagep = page;
- return count;
-}
-#endif
-
#ifdef CONFIG_HIBERNATION
/*
* Find the swap type that corresponds to given device (if any).
--
1.7.4.1
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