Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210208085013.89436-5-songmuchun@bytedance.com>
 <YCafit5ruRJ+SL8I@dhcp22.suse.cz> <CAMZfGtXgVUvCejpxu1o5WDvmQ7S88rWqGi3DAGM6j5NHJgtdcg@mail.gmail.com>
 <YCpN38i75olgispI@dhcp22.suse.cz> <CAMZfGtUXJTaMo36aB4nTFuYFy3qfWW69o=4uUo-FjocO8obDgw@mail.gmail.com>
 <CAMZfGtWT8CJ-QpVofB2X-+R7GE7sMa40eiAJm6PyD0ji=FzBYQ@mail.gmail.com>
 <YCpmlGuoTakPJs1u@dhcp22.suse.cz> <CAMZfGtWd_ZaXtiEdMKhpnAHDw5CTm-CSPSXW+GfKhyX5qQK=Og@mail.gmail.com>
 <YCp04NVBZpZZ5k7G@dhcp22.suse.cz> <CAMZfGtV8-yJa_eGYtSXc0YY8KhYpgUo=pfj6TZ9zMo8fbz8nWA@mail.gmail.com>
 <YCqhDZ0EAgvCz+wX@dhcp22.suse.cz>
In-Reply-To: <YCqhDZ0EAgvCz+wX@dhcp22.suse.cz>
From:   Muchun Song <songmuchun@bytedance.com>
Date:   Tue, 16 Feb 2021 01:48:29 +0800
Message-ID: <CAMZfGtW6n_YUbZOPFbivzn-HP4Q2yi0DrUoQ3JAjSYy5m17VWw@mail.gmail.com>
Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap
 pages associated with each HugeTLB page
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>,
        =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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.

> --
> Michal Hocko
> SUSE Labs