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

From: Michal Hocko <mhocko@suse.com>
To: Muchun Song <songmuchun@bytedance.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: Mon, 15 Feb 2021 20:39:15 +0100	[thread overview]
Message-ID: <YCrN4/EWRTOwNw72@dhcp22.suse.cz> (raw)
In-Reply-To: <CAMZfGtWVwEdBfiof3=wW2-FUN4PU-N5J=HfiAETVbwbEzdvAGQ@mail.gmail.com>

On Tue 16-02-21 02:19:20, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 1:48 AM Muchun Song <songmuchun@bytedance.com> wrote:
> >
> > On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Mon 15-02-21 23:36:49, Muchun Song wrote:
> > > [...]
> > > > > There shouldn't be any real reason why the memory allocation for
> > > > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > > > can be deferred to a more relaxed context. If you want to make a
> > > >
> > > > Yeah, you are right. We can put the freeing hugetlb routine to a
> > > > workqueue. Just like I do in the previous version (before v13) patch.
> > > > I will pick up these patches.
> > >
> > > I haven't seen your v13 and I will unlikely have time to revisit that
> > > version. I just wanted to point out that the actual allocation doesn't
> > > have to happen from under the spinlock. There are multiple ways to go
> > > around that. Dropping the lock would be one of them. Preallocation
> > > before the spin lock is taken is another. WQ is certainly an option but
> > > I would take it as the last resort when other paths are not feasible.
> > >
> >
> > "Dropping the lock" and "Preallocation before the spin lock" can limit
> > the context of put_page to non-atomic context. I am not sure if there
> > is a page puted somewhere under an atomic context. e.g. compaction.
> > I am not an expert on this.
> 
> 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.
-- 
Michal Hocko
SUSE Labs