linux-kernel - Re: [External] Re: [PATCH v2 03/19] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE

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Message-ID: <CAMZfGtVrKrvn0J7jVYjppRv_mF3y-e8RnL7aQRsqPLjfXH8T5Q@mail.gmail.com>
Date:   Thu, 29 Oct 2020 21:34:22 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Oscar Salvador <osalvador@...e.de>
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>,
        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 v2 03/19] mm/hugetlb: Introduce a new
 config HUGETLB_PAGE_FREE_VMEMMAP

On Thu, Oct 29, 2020 at 6:29 PM Oscar Salvador <osalvador@...e.de> wrote:
>
> On Mon, Oct 26, 2020 at 10:50:58PM +0800, Muchun Song wrote:
> > The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
> > whether to enable the feature of freeing unused vmemmap associated
> > with HugeTLB pages. Now only support x86.
>
> Why this needs to be a config thing?
> If this space-memory-optimization does not come with a trade-off,
> why does the user have to set this instead of coming by default?

Now we only support x86_64. If we want to support other archs. We
need some arch special code to support this feature. In the future,
if this patch series is merged to mainline, I will implement this
optimization for other archs. At that time we can remove the
HUGETLB_PAGE_FREE_VMEMMAP.

Thanks.

>
>
> --
> Oscar Salvador
> SUSE L3



-- 
Yours,
Muchun