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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Tue, 16 Feb 2021 02:19:20 +0800
Message-ID: <CAMZfGtWVwEdBfiof3=wW2-FUN4PU-N5J=HfiAETVbwbEzdvAGQ@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>,
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        <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>
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On Tue, Feb 16, 2021 at 1:48 AM Muchun Song <songmuchun@bytedance.com> wrot=
e:
>
> 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 withi=
n the
> > > > hugetlb lock and therefore requiring a non-sleeping semantic. All t=
hat
> > > > 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=EF=BC=9FIf no=
t,
WQ may be the only option and it also will not limit the context of
put_page. Right?

>
> > --
> > Michal Hocko
> > SUSE Labs