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From: Roman Gushchin <guro@fb.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: <hannes@cmpxchg.org>, <mhocko@kernel.org>,
	<akpm@linux-foundation.org>, <shakeelb@google.com>,
	<vdavydov.dev@gmail.com>, <linux-kernel@vger.kernel.org>,
	<linux-mm@kvack.org>, <duanxiongchun@bytedance.com>,
	<fam.zheng@bytedance.com>, <bsingharora@gmail.com>,
	<shy828301@gmail.com>, <alexs@kernel.org>, <smuchun@gmail.com>,
	<zhengqi.arch@bytedance.com>
Subject: Re: [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented
Date: Tue, 17 Aug 2021 20:18:01 -0700	[thread overview]
Message-ID: <YRx76SlTkTT8a1BI@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210814052519.86679-4-songmuchun@bytedance.com>

On Sat, Aug 14, 2021 at 01:25:10PM +0800, Muchun Song wrote:
> The diagram below shows how to make the folio lruvec lock safe when LRU
> pages are reparented.
> 
> folio_lruvec_lock(folio)
>     retry:
> 	lruvec = folio_lruvec(folio);
> 
>         // The folio is reparented at this time.
>         spin_lock(&lruvec->lru_lock);
> 
>         if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio)))
>             // Acquired the wrong lruvec lock and need to retry.
>             // Because this folio is on the parent memcg lruvec list.
>             goto retry;
> 
>         // If we reach here, it means that folio_memcg(folio) is stable.
> 
> memcg_reparent_objcgs(memcg)
>     // lruvec belongs to memcg and lruvec_parent belongs to parent memcg.
>     spin_lock(&lruvec->lru_lock);
>     spin_lock(&lruvec_parent->lru_lock);
> 
>     // Move all the pages from the lruvec list to the parent lruvec list.
> 
>     spin_unlock(&lruvec_parent->lru_lock);
>     spin_unlock(&lruvec->lru_lock);
> 
> After we acquire the lruvec lock, we need to check whether the folio is
> reparented. If so, we need to reacquire the new lruvec lock. On the
> routine of the LRU pages reparenting, we will also acquire the lruvec
> lock (will be implemented in the later patch). So folio_memcg() cannot
> be changed when we hold the lruvec lock.
> 
> Since lruvec_memcg(lruvec) is always equal to folio_memcg(folio) after
> we hold the lruvec lock, lruvec_memcg_debug() check is pointless. So
> remove it.
> 
> This is a preparation for reparenting the LRU pages.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Roman Gushchin <guro@fb.com>

Maybe it's mostly s/page/folio, but the patch looks quite differently
in comparison to the version I did ack. In general, please, drop acks
when there are significant changes between versions.

Thanks!

  reply	other threads:[~2021-08-18  3:18 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-14  5:25 [PATCH v1 00/12] Use obj_cgroup APIs to charge the LRU pages Muchun Song
2021-08-14  5:25 ` [PATCH v1 01/12] mm: memcontrol: prepare objcg API for non-kmem usage Muchun Song
2021-08-14 22:23   ` kernel test robot
2021-08-18  3:01   ` Roman Gushchin
2021-08-20  6:44     ` Muchun Song
2021-08-14  5:25 ` [PATCH v1 02/12] mm: memcontrol: introduce compact_folio_lruvec_lock_irqsave Muchun Song
2021-08-14  5:25 ` [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented Muchun Song
2021-08-18  3:18   ` Roman Gushchin [this message]
2021-08-18  4:28     ` Muchun Song
2021-08-18  4:47       ` Roman Gushchin
2021-08-14  5:25 ` [PATCH v1 04/12] mm: vmscan: rework move_pages_to_lru() Muchun Song
2021-08-14  5:25 ` [PATCH v1 05/12] mm: thp: introduce folio_split_queue_lock{_irqsave}() Muchun Song
2021-08-14  8:22   ` kernel test robot
2021-08-14 10:38   ` kernel test robot
2021-08-14  5:25 ` [PATCH v1 06/12] mm: thp: make split queue lock safe when LRU pages are reparented Muchun Song
2021-08-14  5:25 ` [PATCH v1 07/12] mm: memcontrol: make all the callers of {folio,page}_memcg() safe Muchun Song
2021-08-14  5:25 ` [PATCH v1 08/12] mm: memcontrol: introduce memcg_reparent_ops Muchun Song
2021-08-14  5:25 ` [PATCH v1 09/12] mm: memcontrol: use obj_cgroup APIs to charge the LRU pages Muchun Song
2021-08-14 14:08   ` kernel test robot
2021-08-14  5:25 ` [PATCH v1 10/12] mm: memcontrol: rename {un}lock_page_memcg() to {un}lock_page_objcg() Muchun Song
2021-08-14  5:25 ` [PATCH v1 11/12] mm: lru: add VM_BUG_ON_FOLIO to lru maintenance function Muchun Song
2021-08-14  5:25 ` [PATCH v1 12/12] mm: lru: use lruvec lock to serialize memcg changes Muchun Song

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