linux-kernel - Re: [External] Re: [PATCH v4 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers

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Date:   Tue, 17 Nov 2020 23:29:45 +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>,
        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 v4 05/21] mm/hugetlb: Introduce pgtable
 allocation/freeing helpers

On Tue, Nov 17, 2020 at 11:06 PM Oscar Salvador <osalvador@...e.de> wrote:
>
> On Fri, Nov 13, 2020 at 06:59:36PM +0800, Muchun Song wrote:
> > +#define page_huge_pte(page)          ((page)->pmd_huge_pte)

Yeah, I forgot to remove it. Thanks.

>
> Seems you do not need this one anymore.
>
> > +void vmemmap_pgtable_free(struct page *page)
> > +{
> > +     struct page *pte_page, *t_page;
> > +
> > +     list_for_each_entry_safe(pte_page, t_page, &page->lru, lru) {
> > +             list_del(&pte_page->lru);
> > +             pte_free_kernel(&init_mm, page_to_virt(pte_page));
> > +     }
> > +}
> > +
> > +int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> > +{
> > +     unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> > +
> > +     /* Store preallocated pages on huge page lru list */
> > +     INIT_LIST_HEAD(&page->lru);
> > +
> > +     while (nr--) {
> > +             pte_t *pte_p;
> > +
> > +             pte_p = pte_alloc_one_kernel(&init_mm);
> > +             if (!pte_p)
> > +                     goto out;
> > +             list_add(&virt_to_page(pte_p)->lru, &page->lru);
> > +     }
>
> Definetely this looks better and easier to handle.
> Btw, did you explore Matthew's hint about instead of allocating a new page,
> using one of the ones you are going to free to store the ptes?

Oh, sorry for missing his reply. It is a good idea. I will start an
investigation.
Thanks for reminding me.

> I am not sure whether it is feasible at all though.
>
>
> > --- a/mm/hugetlb_vmemmap.h
> > +++ b/mm/hugetlb_vmemmap.h
> > @@ -9,12 +9,24 @@
> >  #ifndef _LINUX_HUGETLB_VMEMMAP_H
> >  #define _LINUX_HUGETLB_VMEMMAP_H
> >  #include <linux/hugetlb.h>
> > +#include <linux/mm.h>
>
> why do we need this here?

Yeah, also can remove:).


>
> --
> Oscar Salvador
> SUSE L3



--
Yours,
Muchun