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Message-Id: <20101007162811.c3a35be9.nishimura@mxp.nes.nec.co.jp>
Date: Thu, 7 Oct 2010 16:28:11 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Minchan Kim <minchan.kim@...il.com>,
Greg Thelen <gthelen@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH] memcg: reduce lock time at move charge (Was Re: [PATCH
04/10] memcg: disable local interrupts in lock_page_cgroup()
On Thu, 7 Oct 2010 15:21:11 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Thu, 7 Oct 2010 11:17:43 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
> > > hmm, if we'll do that, I think we need to do that under pte_lock in
> > > mem_cgroup_move_charge_pte_range(). But, we can't do wait_on_page_writeback()
> > > under pte_lock, right? Or, we need re-organize current move-charge implementation.
> > >
> > Nice catch. I think releaseing pte_lock() is okay. (and it should be released)
> >
> > IIUC, task's css_set() points to new cgroup when "move" is called. Then,
> > it's not necessary to take pte_lock, I guess.
> > (And taking pte_lock too long is not appreciated..)
> >
> > I'll write a sample patch today.
> >
> Here.
Great!
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> 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(2nd) level page table.
>
> This pte_offset_map_lock seems a bit long. This patch modifies a rountine as
>
> pte_offset_map_lock()
> for 32 pages:
> 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()
>
> Note: newly-charged pages while we move account are charged to the new group.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/memcontrol.c | 92 ++++++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 60 insertions(+), 32 deletions(-)
>
> Index: mmotm-0928/mm/memcontrol.c
> ===================================================================
> --- mmotm-0928.orig/mm/memcontrol.c
> +++ mmotm-0928/mm/memcontrol.c
> @@ -4475,17 +4475,22 @@ 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_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;
> +};
> +
> +
> static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
> unsigned long addr, pte_t ptent)
> {
> @@ -4561,7 +4566,7 @@ 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 +4592,7 @@ 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 +4602,10 @@ 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;
> }
>
> @@ -4751,6 +4758,9 @@ static void mem_cgroup_cancel_attach(str
> mem_cgroup_clear_mc();
> }
>
> +
> +#define MC_MOVE_ONCE (32)
> +
> static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> unsigned long addr, unsigned long end,
> struct mm_walk *walk)
> @@ -4759,26 +4769,47 @@ static int mem_cgroup_move_charge_pte_ra
> struct vm_area_struct *vma = walk->private;
> pte_t *pte;
> spinlock_t *ptl;
> + struct mc_target *target;
> + int index, num;
> +
> + target = kzalloc(sizeof(struct mc_target) *MC_MOVE_ONCE, GFP_KERNEL);
hmm? I can't see it freed anywhere.
Considering you reset target[]->type to MC_TARGET_NONE, do you intended to
reuse targe[] while walking the page table ?
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() ?
Thanks,
Daisuke Nishimura.
> + if (!target)
> + return -ENOMEM;
>
> 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, &target[num]);
> + if (!ret)
> + continue;
> + 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 = &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 +4818,9 @@ 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 +4831,20 @@ put: /* is_target_pte_for_mc() gets th
> default:
> break;
> }
> + } while (index < num);
> +out:
> + for (index = 0; index < num; index++) {
> + if (target[index].type == MC_TARGET_PAGE)
> + put_page(target[index].val.page);
> + 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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