linux-kernel - Re: [RFC PATCH v3 02/12] mm: memcontrol: introduce compact_lock_page_lruvec

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Message-ID: <YK0yBhDj+9zJlz/d@carbon.dhcp.thefacebook.com>
Date:   Tue, 25 May 2021 10:21:10 -0700
From:   Roman Gushchin <guro@...com>
To:     Muchun Song <songmuchun@...edance.com>
CC:     <hannes@...xchg.org>, <mhocko@...nel.org>,
        <akpm@...ux-foundation.org>, <shakeelb@...gle.com>,
        <vdavydov.dev@...il.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <duanxiongchun@...edance.com>,
        <fam.zheng@...edance.com>, <bsingharora@...il.com>,
        <shy828301@...il.com>, <alex.shi@...ux.alibaba.com>
Subject: Re: [RFC PATCH v3 02/12] mm: memcontrol: introduce
 compact_lock_page_lruvec_irqsave

On Wed, Apr 21, 2021 at 03:00:49PM +0800, Muchun Song wrote:
> If we reuse the objcg APIs to charge LRU pages, the page_memcg()
> can be changed when the LRU pages reparented. In this case, we need
> to acquire the new lruvec lock.
> 
>     lruvec = mem_cgroup_page_lruvec(page);
> 
>     // The page is reparented.
> 
>     compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
> 
>     // Acquired the wrong lruvec lock and need to retry.
> 
> But compact_lock_irqsave() only take lruvec lock as the parameter,
> we cannot aware this change. If it can take the page as parameter
> to acquire the lruvec lock. When the page memcg is changed, we can
> use the page_memcg() detect whether we need to reacquire the new
> lruvec lock. So compact_lock_irqsave() is not suitable for us.
> Similar to lock_page_lruvec_irqsave(), introduce
> compact_lock_page_lruvec_irqsave() to acquire the lruvec lock in
> the compaction routine.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Acked-by: Roman Gushchin <guro@...com>

> ---
>  mm/compaction.c | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 1c500e697c88..082293587cc6 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -511,6 +511,29 @@ static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
>  	return true;
>  }
>  
> +static struct lruvec *
> +compact_lock_page_lruvec_irqsave(struct page *page, unsigned long *flags,
> +				 struct compact_control *cc)

Maybe compact_lock_page_irqsave() to make it more similar to
compact_lock_irqsafe()? But it's up to you.

Thanks!