linux-kernel - Re: [PATCH v2 07/11] hugetlb: perform vmemmap restoration on a list of pages

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Message-ID: <20230906205319.GB3612@monkey>
Date:   Wed, 6 Sep 2023 13:53:19 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <muchun.song@...ux.dev>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 07/11] hugetlb: perform vmemmap restoration on a list
 of pages

On 09/06/23 15:33, Muchun Song wrote:
> 
> 
> On 2023/9/6 05:44, Mike Kravetz wrote:
> > When removing hugetlb pages from the pool, we first create a list
> > of removed pages and then free those pages back to low level allocators.
> > Part of the 'freeing process' is to restore vmemmap for all base pages
> > if necessary.  Pass this list of pages to a new routine
> > hugetlb_vmemmap_restore_folios() so that vmemmap restoration can be
> > performed in bulk.
> > 
> > Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> > ---
> >   mm/hugetlb.c         |  3 +++
> >   mm/hugetlb_vmemmap.c | 13 +++++++++++++
> >   mm/hugetlb_vmemmap.h |  5 +++++
> >   3 files changed, 21 insertions(+)
> > 
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 554be94b07bd..dd2dbc256172 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1838,6 +1838,9 @@ static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
> >   {
> >   	struct folio *folio, *t_folio;
> > +	/* First restore vmemmap for all pages on list. */
> > +	hugetlb_vmemmap_restore_folios(h, list);
> > +
> >   	list_for_each_entry_safe(folio, t_folio, list, lru) {
> >   		update_and_free_hugetlb_folio(h, folio, false);
> >   		cond_resched();
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index ac5577d372fe..79de984919ef 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -481,6 +481,19 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
> >   	return ret;
> >   }
> > +/*
> > + * This function will attempt to resore vmemmap for a list of folios.  There
> > + * is no guarantee that restoration will be successful for all or any folios.
> > + * This is used in bulk operations, and no feedback is given to the caller.
> > + */
> > +void hugetlb_vmemmap_restore_folios(const struct hstate *h, struct list_head *folio_list)
> > +{
> > +	struct folio *folio;
> > +
> > +	list_for_each_entry(folio, folio_list, lru)
> > +		(void)hugetlb_vmemmap_restore(h, &folio->page);
> 
> I am curious about the purpose of "void" here, seems it it not necessnary,
> ritgh? We cound see so many palces where we do not add the void if the
> caller
> does not care about the return value of the callee.

Yes, we can drop the (void).  Sorry about adding that.

-- 
Mike Kravetz