linux-kernel - Re: [External] Re: [PATCH v3 09/21] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page

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Message-ID: <20201110135210.GA29463@linux>
Date:   Tue, 10 Nov 2020 14:52:15 +0100
From:   Oscar Salvador <osalvador@...e.de>
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>,
        Michal Hocko <mhocko@...e.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 v3 09/21] mm/hugetlb: Free the vmemmap
 pages associated with each hugetlb page

On Tue, Nov 10, 2020 at 06:47:08PM +0800, Muchun Song wrote:
> > That only refers to gigantic pages, right?
> 
> Yeah, now it only refers to gigantic pages. Originally, I also wanted to merge
> vmemmap PTE to PMD for normal 2MB HugeTLB pages. So I introduced
> those macros(e.g. freed_vmemmap_hpage). For 2MB HugeTLB pages, I
> haven't found an elegant solution. Hopefully, when you or someone have
> read all of the patch series, we can come up with an elegant solution to
> merge PTE.

Well, it is quite a lot of "tricky" code, so it takes some time.

> > > > > +static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> > > > > +{
> > > > > +     pmd_t *pmd;
> > > > > +     spinlock_t *ptl;
> > > > > +     LIST_HEAD(free_pages);
> > > > > +
> > > > > +     if (!free_vmemmap_pages_per_hpage(h))
> > > > > +             return;
> > > > > +
> > > > > +     pmd = vmemmap_to_pmd(head);
> > > > > +     ptl = vmemmap_pmd_lock(pmd);

I forgot about this one.
You might want to check whether vmemmap_to_pmd returns NULL or not.
If it does means that something went wrong anyways, but still we should handle
such case (and print a fat warning or something like that).


-- 
Oscar Salvador
SUSE L3