[PATCH v2] memcg: reduce lock time at move charge (Was Re: [PATCH04/10] memcg: disable local interrupts in lock_page_cgroup()

From: KAMEZAWA Hiroyuki
Date: Thu Oct 07 2010 - 04:09:37 EST

On Thu, 7 Oct 2010 16:42:04 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > If so, how about adding a new member(struct mc_target *targe) to move_charge_struct,
> > and allocate/free it at mem_cgroup_move_charge() ?
> >
> Hmm, sounds nice.
>

Here.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

Now, at task migration among cgroup, memory cgroup scans page table and moving
account if flags are properly set.

The core code, mem_cgroup_move_charge_pte_range() does

pte_offset_map_lock();
for all ptes in a page table:
1. look into page table, find_and_get a page
2. remove it from LRU.
3. move charge.
4. putback to LRU. put_page()
pte_offset_map_unlock();

for pte entries on a 3rd level? page table.

This pte_offset_map_lock seems a bit long. This patch modifies a rountine as

for 32 pages: pte_offset_map_lock()
find_and_get a page
record it
pte_offset_map_unlock()
for all recorded pages
isolate it from LRU.
move charge
putback to LRU
for all recorded pages
put_page()

Changelog: v1->v2
- removed kzalloc() of mc_target. preallocate it on "mc"

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 95 ++++++++++++++++++++++++++++++++++----------------------
1 file changed, 59 insertions(+), 36 deletions(-)

Index: mmotm-0928/mm/memcontrol.c
===================================================================
--- mmotm-0928.orig/mm/memcontrol.c
+++ mmotm-0928/mm/memcontrol.c
@@ -276,6 +276,21 @@ enum move_type {
NR_MOVE_TYPE,
};

+enum mc_target_type {
+ MC_TARGET_NONE, /* used as failure code(0) */
+ MC_TARGET_PAGE,
+ MC_TARGET_SWAP,
+};
+
+struct mc_target {
+ enum mc_target_type type;
+ union {
+ struct page *page;
+ swp_entry_t ent;
+ } val;
+};
+#define MC_MOVE_ONCE (32)
+
/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
spinlock_t lock; /* for from, to, moving_task */
@@ -284,6 +299,7 @@ static struct move_charge_struct {
unsigned long precharge;
unsigned long moved_charge;
unsigned long moved_swap;
+ struct mc_target target[MC_MOVE_ONCE];
struct task_struct *moving_task; /* a task moving charges */
wait_queue_head_t waitq; /* a waitq for other context */
} mc = {
@@ -291,6 +307,7 @@ static struct move_charge_struct {
.waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};

+
static bool move_anon(void)
{
return test_bit(MOVE_CHARGE_TYPE_ANON,
@@ -4475,16 +4492,7 @@ one_by_one:
*
* Called with pte lock held.
*/
-union mc_target {
- struct page *page;
- swp_entry_t ent;
-};

-enum mc_target_type {
- MC_TARGET_NONE, /* not used */
- MC_TARGET_PAGE,
- MC_TARGET_SWAP,
-};

static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
unsigned long addr, pte_t ptent)
@@ -4561,7 +4569,7 @@ static struct page *mc_handle_file_pte(s
}

static int is_target_pte_for_mc(struct vm_area_struct *vma,
- unsigned long addr, pte_t ptent, union mc_target *target)
+ unsigned long addr, pte_t ptent, struct mc_target *target)
{
struct page *page = NULL;
struct page_cgroup *pc;
@@ -4587,7 +4595,7 @@ static int is_target_pte_for_mc(struct v
if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
ret = MC_TARGET_PAGE;
if (target)
- target->page = page;
+ target->val.page = page;
}
if (!ret || !target)
put_page(page);
@@ -4597,8 +4605,10 @@ static int is_target_pte_for_mc(struct v
css_id(&mc.from->css) == lookup_swap_cgroup(ent)) {
ret = MC_TARGET_SWAP;
if (target)
- target->ent = ent;
+ target->val.ent = ent;
}
+ if (target)
+ target->type = ret;
return ret;
}

@@ -4759,26 +4769,42 @@ static int mem_cgroup_move_charge_pte_ra
struct vm_area_struct *vma = walk->private;
pte_t *pte;
spinlock_t *ptl;
+ int index, num;

retry:
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
- for (; addr != end; addr += PAGE_SIZE) {
+ for (num = 0; num < MC_MOVE_ONCE && addr != end; addr += PAGE_SIZE) {
pte_t ptent = *(pte++);
- union mc_target target;
- int type;
+ ret = is_target_pte_for_mc(vma, addr, ptent, &mc.target[num]);
+ if (!ret)
+ continue;
+ mc.target[num++].type = ret;
+ }
+ pte_unmap_unlock(pte - 1, ptl);
+ cond_resched();
+
+ ret = 0;
+ index = 0;
+ do {
+ struct mc_target *mt;
struct page *page;
struct page_cgroup *pc;
swp_entry_t ent;

- if (!mc.precharge)
- break;
+ if (!mc.precharge) {
+ ret = mem_cgroup_do_precharge(1);
+ if (ret)
+ goto out;
+ continue;
+ }
+
+ mt = &mc.target[index++];

- type = is_target_pte_for_mc(vma, addr, ptent, &target);
- switch (type) {
+ switch (mt->type) {
case MC_TARGET_PAGE:
- page = target.page;
+ page = mt->val.page;
if (isolate_lru_page(page))
- goto put;
+ break;
pc = lookup_page_cgroup(page);
if (!mem_cgroup_move_account(pc,
mc.from, mc.to, false)) {
@@ -4787,11 +4813,9 @@ retry:
mc.moved_charge++;
}
putback_lru_page(page);
-put: /* is_target_pte_for_mc() gets the page */
- put_page(page);
break;
case MC_TARGET_SWAP:
- ent = target.ent;
+ ent = mt->val.ent;
if (!mem_cgroup_move_swap_account(ent,
mc.from, mc.to, false)) {
mc.precharge--;
@@ -4802,21 +4826,20 @@ put: /* is_target_pte_for_mc() gets th
default:
break;
}
+ } while (index < num);
+out:
+ for (index = 0; index < num; index++) {
+ if (mc.target[index].type == MC_TARGET_PAGE)
+ put_page(mc.target[index].val.page);
+ mc.target[index].type = MC_TARGET_NONE;
}
- pte_unmap_unlock(pte - 1, ptl);
+
+ if (ret)
+ return ret;
cond_resched();

- if (addr != end) {
- /*
- * We have consumed all precharges we got in can_attach().
- * We try charge one by one, but don't do any additional
- * charges to mc.to if we have failed in charge once in attach()
- * phase.
- */
- ret = mem_cgroup_do_precharge(1);
- if (!ret)
- goto retry;
- }
+ if (addr != end)
+ goto retry;

return ret;
}

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