linux-kernel - Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page

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Message-ID: <20200915143241.GH5449@casper.infradead.org>
Date:   Tue, 15 Sep 2020 15:32:41 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb
 page

On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> This patch series will free some vmemmap pages(struct page structures)
> associated with each hugetlbpage when preallocated to save memory.

It would be lovely to be able to do this.  Unfortunately, it's completely
impossible right now.  Consider, for example, get_user_pages() called
on the fifth page of a hugetlb page.

I've spent a lot of time thinking about this, and there's a lot of work
that needs to happen before we can do this, mostly in device drivers.
Do you want to help?  It's a multi-year project.