From: Johannes Weiner <hannes@cmpxchg.org>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, akpm@linux-foundation.org,
mgorman@techsingularity.net, tj@kernel.org, hughd@google.com,
khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com,
yang.shi@linux.alibaba.com, willy@infradead.org,
shakeelb@google.com, "Michal Hocko" <mhocko@kernel.org>,
"Vladimir Davydov" <vdavydov.dev@gmail.com>,
"Roman Gushchin" <guro@fb.com>,
"Chris Down" <chris@chrisdown.name>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vlastimil Babka" <vbabka@suse.cz>, "Qian Cai" <cai@lca.pw>,
"Andrey Ryabinin" <aryabinin@virtuozzo.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"David Rientjes" <rientjes@google.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
swkhack <swkhack@gmail.com>,
"Potyra, Stefan" <Stefan.Potyra@elektrobit.com>,
"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
"Stephen Rothwell" <sfr@canb.auug.org.au>,
"Colin Ian King" <colin.king@canonical.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
"Peng Fan" <peng.fan@nxp.com>,
"Nikolay Borisov" <nborisov@suse.com>,
"Ira Weiny" <ira.weiny@intel.com>,
"Kirill Tkhai" <ktkhai@virtuozzo.com>,
"Yafang Shao" <laoar.shao@gmail.com>
Subject: Re: [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock
Date: Thu, 21 Nov 2019 17:06:13 -0500 [thread overview]
Message-ID: <20191121220613.GB487872@cmpxchg.org> (raw)
In-Reply-To: <bcf6a952-5b92-50ad-cfc1-f4d9f8f63172@linux.alibaba.com>
On Wed, Nov 20, 2019 at 07:41:44PM +0800, Alex Shi wrote:
> 在 2019/11/20 上午12:04, Johannes Weiner 写道:
> >> @@ -1246,6 +1245,46 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
> >> return lruvec;
> >> }
> >>
> >> +struct lruvec *lock_page_lruvec_irq(struct page *page,
> >> + struct pglist_data *pgdat)
> >> +{
> >> + struct lruvec *lruvec;
> >> +
> >> +again:
> >> + rcu_read_lock();
> >> + lruvec = mem_cgroup_page_lruvec(page, pgdat);
> >> + spin_lock_irq(&lruvec->lru_lock);
> >> + rcu_read_unlock();
> > The spinlock doesn't prevent the lruvec from being freed
> >
> > You deleted the rules from the mem_cgroup_page_lruvec() documentation,
> > but they still apply: if the page is already !PageLRU() by the time
> > you get here, it could get reclaimed or migrated to another cgroup,
> > and that can free the memcg/lruvec. Merely having the lru_lock held
> > does not prevent this.
>
>
> Forgive my idiot, I still don't know the details of unsafe lruvec here.
> From my shortsight, the spin_lock_irq(embedded a preempt_disable) could block all rcu syncing thus, keep all memcg alive until the preempt_enabled in unspinlock, is this right?
> If so even the page->mem_cgroup is migrated to others cgroups, the new and old cgroup should still be alive here.
You are right about the freeing part, I missed this. And I should have
read this email here before sending out my "fix" to the current code;
thankfully Hugh re-iterated my mistake on that thread. My apologies.
But I still don't understand how the moving part is safe. You look up
the lruvec optimistically, lock it, then verify the lookup. What keeps
page->mem_cgroup from changing after you verified it?
lock_page_lruvec(): mem_cgroup_move_account():
again:
rcu_read_lock()
lruvec = page->mem_cgroup->lruvec
isolate_lru_page()
spin_lock_irq(&lruvec->lru_lock)
rcu_read_unlock()
if page->mem_cgroup->lruvec != lruvec:
spin_unlock_irq(&lruvec->lru_lock)
goto again;
page->mem_cgroup = new cgroup
putback_lru_page() // new lruvec
SetPageLRU()
return lruvec; // old lruvec
The caller assumes page belongs to the returned lruvec and will then
change the page's lru state with a mismatched page and lruvec.
If we could restrict lock_page_lruvec() to working only on PageLRU
pages, we could fix the problem with memory barriers. But this won't
work for split_huge_page(), which is AFAICT the only user that needs
to freeze the lru state of a page that could be isolated elsewhere.
So AFAICS the only option is to lock out mem_cgroup_move_account()
entirely when the lru_lock is held. Which I guess should be fine.
next prev parent reply other threads:[~2019-11-21 22:06 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 12:23 [PATCH v4 0/9] per lruvec lru_lock for memcg Alex Shi
2019-11-19 12:23 ` [PATCH v4 1/9] mm/swap: fix uninitialized compiler warning Alex Shi
2019-11-19 15:41 ` Johannes Weiner
2019-11-20 11:42 ` Alex Shi
2019-11-19 12:23 ` [PATCH v4 2/9] mm/huge_memory: " Alex Shi
2019-11-19 15:42 ` Johannes Weiner
2019-11-19 12:23 ` [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2019-11-19 15:57 ` Matthew Wilcox
2019-11-19 16:44 ` Johannes Weiner
2019-11-20 11:50 ` Alex Shi
2019-11-19 16:04 ` Johannes Weiner
2019-11-20 11:41 ` Alex Shi
2019-11-21 22:06 ` Johannes Weiner [this message]
2019-11-22 2:36 ` Alex Shi
2019-11-22 16:16 ` Johannes Weiner
2019-11-23 0:58 ` Hugh Dickins
2019-11-24 15:19 ` Alex Shi
2019-11-25 9:26 ` Alex Shi
2019-11-25 17:27 ` Shakeel Butt
2019-11-19 16:49 ` Shakeel Butt
2019-11-19 12:23 ` [PATCH v4 4/9] mm/mlock: only change the lru_lock iff page's lruvec is different Alex Shi
2019-11-19 12:23 ` [PATCH v4 5/9] mm/swap: " Alex Shi
2019-11-19 12:23 ` [PATCH v4 6/9] mm/vmscan: " Alex Shi
2019-11-19 12:23 ` [PATCH v4 7/9] mm/pgdat: remove pgdat lru_lock Alex Shi
2019-11-19 12:23 ` [PATCH v4 8/9] mm/lru: likely enhancement Alex Shi
2019-11-19 12:23 ` [PATCH v4 9/9] mm/lru: revise the comments of lru_lock Alex Shi
2019-11-19 16:19 ` Johannes Weiner
2019-11-20 11:48 ` Alex Shi
2019-11-24 15:49 ` [PATCH v4 0/9] per lruvec lru_lock for memcg Konstantin Khlebnikov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191121220613.GB487872@cmpxchg.org \
--to=hannes@cmpxchg.org \
--cc=Stefan.Potyra@elektrobit.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=alex.shi@linux.alibaba.com \
--cc=aneesh.kumar@linux.ibm.com \
--cc=aryabinin@virtuozzo.com \
--cc=cai@lca.pw \
--cc=cgroups@vger.kernel.org \
--cc=chris@chrisdown.name \
--cc=colin.king@canonical.com \
--cc=daniel.m.jordan@oracle.com \
--cc=guro@fb.com \
--cc=hughd@google.com \
--cc=ira.weiny@intel.com \
--cc=jgg@ziepe.ca \
--cc=jglisse@redhat.com \
--cc=khlebnikov@yandex-team.ru \
--cc=kirill.shutemov@linux.intel.com \
--cc=ktkhai@virtuozzo.com \
--cc=laoar.shao@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mchehab+samsung@kernel.org \
--cc=mgorman@techsingularity.net \
--cc=mhocko@kernel.org \
--cc=nborisov@suse.com \
--cc=peng.fan@nxp.com \
--cc=rientjes@google.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=sfr@canb.auug.org.au \
--cc=shakeelb@google.com \
--cc=swkhack@gmail.com \
--cc=tglx@linutronix.de \
--cc=tj@kernel.org \
--cc=vbabka@suse.cz \
--cc=vdavydov.dev@gmail.com \
--cc=willy@infradead.org \
--cc=yang.shi@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).