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From: Muchun Song <songmuchun@bytedance.com>
To: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shakeel Butt <shakeelb@google.com>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Xiongchun duan <duanxiongchun@bytedance.com>,
	fam.zheng@bytedance.com, "Singh, Balbir" <bsingharora@gmail.com>,
	Yang Shi <shy828301@gmail.com>, Alex Shi <alexs@kernel.org>,
	Muchun Song <smuchun@gmail.com>,
	Qi Zheng <zhengqi.arch@bytedance.com>
Subject: Re: [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented
Date: Wed, 18 Aug 2021 12:28:02 +0800	[thread overview]
Message-ID: <CAMZfGtWhQcfFwkTq59ZboHe5iaLqeGhb9M8GzjEMWZwwYxB43w@mail.gmail.com> (raw)
In-Reply-To: <YRx76SlTkTT8a1BI@carbon.dhcp.thefacebook.com>

On Wed, Aug 18, 2021 at 11:18 AM Roman Gushchin <guro@fb.com> wrote:
>
> 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.

Got it. I'll drop all acks in the next version. Thanks.

>
> Thanks!

  reply	other threads:[~2021-08-18  4:28 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
2021-08-18  4:28     ` Muchun Song [this message]
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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