Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

From: Muchun Song <songmuchun@bytedance.com>
To: Michal Hocko <mhocko@suse.com>
Cc: "Jonathan Corbet" <corbet@lwn.net>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	"Peter Zijlstra" <peterz@infradead.org>,
	viro@zeniv.linux.org.uk,
	"Andrew Morton" <akpm@linux-foundation.org>,
	paulmck@kernel.org, mchehab+huawei@kernel.org,
	pawan.kumar.gupta@linux.intel.com,
	"Randy Dunlap" <rdunlap@infradead.org>,
	oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
	"Mina Almasry" <almasrymina@google.com>,
	"David Rientjes" <rientjes@google.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Oscar Salvador" <osalvador@suse.de>,
	"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	"David Hildenbrand" <david@redhat.com>,
	"HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
	"Joao Martins" <joao.m.martins@oracle.com>,
	"Xiongchun duan" <duanxiongchun@bytedance.com>,
	linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	"Linux Memory Management List" <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
Date: Tue, 16 Feb 2021 17:03:42 +0800	[thread overview]
Message-ID: <CAMZfGtVLv7_7sRO0tXiVY_RuAWxTEHz6G=-r7mOXViNhRNPf5A@mail.gmail.com> (raw)
In-Reply-To: <YCt/N9LkJT1VJEW1@dhcp22.suse.cz>

On Tue, Feb 16, 2021 at 4:15 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 16-02-21 12:34:41, Muchun Song wrote:
> > On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@suse.com> wrote:
> [...]
> > > > Using GFP_KERNEL will also use the current task cpuset to allocate
> > > > memory. Do we have an interface to ignore current task cpuset？If not,
> > > > WQ may be the only option and it also will not limit the context of
> > > > put_page. Right?
> > >
> > > Well, GFP_KERNEL is constrained to the task cpuset only if the said
> > > cpuset is hardwalled IIRC. But I do not see why this is a problem.
> >
> > I mean that if there are more than one node in the system,
> > but the current task cpuset only allows one node.
>
> How would that cpuset get a huge pages from a node which is not part of
> the cpuset? Well, that would be possible if the cpuset was dynamic but I
> am not sure that such a configuration would be very sensible along with
> hardwall setup.

Got it. I didn't realize this before. Thanks.

>
> > If current
> > node has no memory and other nodes have enough memory.
> > We can fail to allocate vmemmap pages. But actually it is
> > suitable to allocate vmemmap pages from other nodes.
> > Right?
>
> Falling back to a different node would be very suboptimal because then
> you would have vmemmap back by remote pages. We do not want that.
> --
> Michal Hocko
> SUSE Labs