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

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Date:   Mon, 15 Feb 2021 17:27:57 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap
 pages associated with each HugeTLB page

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.

-- 
Michal Hocko
SUSE Labs