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Date: Tue, 3 Mar 2015 14:45:24 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Chen Gang <762976180@...com>
Cc: hannes@...xchg.org, cgroups@...r.kernel.org, linux-mm@...ck.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: memcontrol: Let mem_cgroup_move_account() have
effect only if MMU enabled
On Tue 03-03-15 06:42:01, Chen Gang wrote:
> When !MMU, it will report warning. The related warning with allmodconfig
> under c6x:
Does it even make any sense to enable CONFIG_MEMCG when !CONFIG_MMU?
Is anybody using this configuration and is it actually usable? My
knowledge about CONFIG_MMU is close to zero so I might be missing
something but I do not see a point into fixing compile warnings when
the whole subsystem is not usable in the first place.
>
> CC mm/memcontrol.o
> mm/memcontrol.c:2802:12: warning: 'mem_cgroup_move_account' defined but not used [-Wunused-function]
> static int mem_cgroup_move_account(struct page *page,
> ^
>
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> ---
> mm/memcontrol.c | 172 ++++++++++++++++++++++++++++----------------------------
> 1 file changed, 86 insertions(+), 86 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0c86945..80f26f5 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2785,92 +2785,6 @@ void mem_cgroup_split_huge_fixup(struct page *head)
> }
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> -/**
> - * mem_cgroup_move_account - move account of the page
> - * @page: the page
> - * @nr_pages: number of regular pages (>1 for huge pages)
> - * @from: mem_cgroup which the page is moved from.
> - * @to: mem_cgroup which the page is moved to. @from != @to.
> - *
> - * The caller must confirm following.
> - * - page is not on LRU (isolate_page() is useful.)
> - * - compound_lock is held when nr_pages > 1
> - *
> - * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
> - * from old cgroup.
> - */
> -static int mem_cgroup_move_account(struct page *page,
> - unsigned int nr_pages,
> - struct mem_cgroup *from,
> - struct mem_cgroup *to)
> -{
> - unsigned long flags;
> - int ret;
> -
> - VM_BUG_ON(from == to);
> - VM_BUG_ON_PAGE(PageLRU(page), page);
> - /*
> - * The page is isolated from LRU. So, collapse function
> - * will not handle this page. But page splitting can happen.
> - * Do this check under compound_page_lock(). The caller should
> - * hold it.
> - */
> - ret = -EBUSY;
> - if (nr_pages > 1 && !PageTransHuge(page))
> - goto out;
> -
> - /*
> - * Prevent mem_cgroup_migrate() from looking at page->mem_cgroup
> - * of its source page while we change it: page migration takes
> - * both pages off the LRU, but page cache replacement doesn't.
> - */
> - if (!trylock_page(page))
> - goto out;
> -
> - ret = -EINVAL;
> - if (page->mem_cgroup != from)
> - goto out_unlock;
> -
> - spin_lock_irqsave(&from->move_lock, flags);
> -
> - if (!PageAnon(page) && page_mapped(page)) {
> - __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
> - nr_pages);
> - __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
> - nr_pages);
> - }
> -
> - if (PageWriteback(page)) {
> - __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_WRITEBACK],
> - nr_pages);
> - __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_WRITEBACK],
> - nr_pages);
> - }
> -
> - /*
> - * It is safe to change page->mem_cgroup here because the page
> - * is referenced, charged, and isolated - we can't race with
> - * uncharging, charging, migration, or LRU putback.
> - */
> -
> - /* caller should have done css_get */
> - page->mem_cgroup = to;
> - spin_unlock_irqrestore(&from->move_lock, flags);
> -
> - ret = 0;
> -
> - local_irq_disable();
> - mem_cgroup_charge_statistics(to, page, nr_pages);
> - memcg_check_events(to, page);
> - mem_cgroup_charge_statistics(from, page, -nr_pages);
> - memcg_check_events(from, page);
> - local_irq_enable();
> -out_unlock:
> - unlock_page(page);
> -out:
> - return ret;
> -}
> -
> #ifdef CONFIG_MEMCG_SWAP
> static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
> bool charge)
> @@ -4822,6 +4736,92 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
> return page;
> }
>
> +/**
> + * mem_cgroup_move_account - move account of the page
> + * @page: the page
> + * @nr_pages: number of regular pages (>1 for huge pages)
> + * @from: mem_cgroup which the page is moved from.
> + * @to: mem_cgroup which the page is moved to. @from != @to.
> + *
> + * The caller must confirm following.
> + * - page is not on LRU (isolate_page() is useful.)
> + * - compound_lock is held when nr_pages > 1
> + *
> + * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
> + * from old cgroup.
> + */
> +static int mem_cgroup_move_account(struct page *page,
> + unsigned int nr_pages,
> + struct mem_cgroup *from,
> + struct mem_cgroup *to)
> +{
> + unsigned long flags;
> + int ret;
> +
> + VM_BUG_ON(from == to);
> + VM_BUG_ON_PAGE(PageLRU(page), page);
> + /*
> + * The page is isolated from LRU. So, collapse function
> + * will not handle this page. But page splitting can happen.
> + * Do this check under compound_page_lock(). The caller should
> + * hold it.
> + */
> + ret = -EBUSY;
> + if (nr_pages > 1 && !PageTransHuge(page))
> + goto out;
> +
> + /*
> + * Prevent mem_cgroup_migrate() from looking at page->mem_cgroup
> + * of its source page while we change it: page migration takes
> + * both pages off the LRU, but page cache replacement doesn't.
> + */
> + if (!trylock_page(page))
> + goto out;
> +
> + ret = -EINVAL;
> + if (page->mem_cgroup != from)
> + goto out_unlock;
> +
> + spin_lock_irqsave(&from->move_lock, flags);
> +
> + if (!PageAnon(page) && page_mapped(page)) {
> + __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
> + nr_pages);
> + __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
> + nr_pages);
> + }
> +
> + if (PageWriteback(page)) {
> + __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_WRITEBACK],
> + nr_pages);
> + __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_WRITEBACK],
> + nr_pages);
> + }
> +
> + /*
> + * It is safe to change page->mem_cgroup here because the page
> + * is referenced, charged, and isolated - we can't race with
> + * uncharging, charging, migration, or LRU putback.
> + */
> +
> + /* caller should have done css_get */
> + page->mem_cgroup = to;
> + spin_unlock_irqrestore(&from->move_lock, flags);
> +
> + ret = 0;
> +
> + local_irq_disable();
> + mem_cgroup_charge_statistics(to, page, nr_pages);
> + memcg_check_events(to, page);
> + mem_cgroup_charge_statistics(from, page, -nr_pages);
> + memcg_check_events(from, page);
> + local_irq_enable();
> +out_unlock:
> + unlock_page(page);
> +out:
> + return ret;
> +}
> +
> static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
> unsigned long addr, pte_t ptent, union mc_target *target)
> {
> --
> 1.9.3
>
>
--
Michal Hocko
SUSE Labs
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