linux-kernel - Re: [PATCH v4 3/8] hugetlb: perform vmemmap optimization on a list of pages

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Date:   Tue, 19 Sep 2023 13:49:54 -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 <21cnbao@...il.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 v4 3/8] hugetlb: perform vmemmap optimization on a list
 of pages

On 09/19/23 11:10, Muchun Song wrote:
> 
> 
> On 2023/9/19 07:01, Mike Kravetz wrote:
> > When adding hugetlb pages to the pool, we first create a list of the
> > allocated pages before adding to the pool.  Pass this list of pages to a
> > new routine hugetlb_vmemmap_optimize_folios() for vmemmap optimization.
> > 
> > Due to significant differences in vmemmmap initialization for bootmem
> > allocated hugetlb pages, a new routine prep_and_add_bootmem_folios
> > is created.
> > 
> > We also modify the routine vmemmap_should_optimize() to check for pages
> > that are already optimized.  There are code paths that might request
> > vmemmap optimization twice and we want to make sure this is not
> > attempted.
> > 
> > Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> > ---
> >   mm/hugetlb.c         | 50 +++++++++++++++++++++++++++++++++++++-------
> >   mm/hugetlb_vmemmap.c | 11 ++++++++++
> >   mm/hugetlb_vmemmap.h |  5 +++++
> >   3 files changed, 58 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 8624286be273..d6f3db3c1313 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -2269,6 +2269,11 @@ static void prep_and_add_allocated_folios(struct hstate *h,
> >   {
> >   	struct folio *folio, *tmp_f;
> > +	/*
> > +	 * Send list for bulk vmemmap optimization processing
> > +	 */
> 
> From the kernel development document, one-line comment format is "/**/".
> 

Will change the comments introduced here.

> > +	hugetlb_vmemmap_optimize_folios(h, folio_list);
> > +
> >   	/*
> >   	 * Add all new pool pages to free lists in one lock cycle
> >   	 */
> > @@ -3309,6 +3314,40 @@ static void __init hugetlb_folio_init_vmemmap(struct folio *folio,
> >   	prep_compound_head((struct page *)folio, huge_page_order(h));
> >   }
> > +static void __init prep_and_add_bootmem_folios(struct hstate *h,
> > +					struct list_head *folio_list)
> > +{
> > +	struct folio *folio, *tmp_f;
> > +
> > +	/*
> > +	 * Send list for bulk vmemmap optimization processing
> > +	 */
> > +	hugetlb_vmemmap_optimize_folios(h, folio_list);
> > +
> > +	/*
> > +	 * Add all new pool pages to free lists in one lock cycle
> > +	 */
> > +	spin_lock_irq(&hugetlb_lock);
> > +	list_for_each_entry_safe(folio, tmp_f, folio_list, lru) {
> > +		if (!folio_test_hugetlb_vmemmap_optimized(folio)) {
> > +			/*
> > +			 * If HVO fails, initialize all tail struct pages
> > +			 * We do not worry about potential long lock hold
> > +			 * time as this is early in boot and there should
> > +			 * be no contention.
> > +			 */
> > +			hugetlb_folio_init_tail_vmemmap(folio,
> > +					HUGETLB_VMEMMAP_RESERVE_PAGES,
> > +					pages_per_huge_page(h));
> > +		}
> > +		__prep_account_new_huge_page(h, folio_nid(folio));
> > +		enqueue_hugetlb_folio(h, folio);
> > +	}
> > +	spin_unlock_irq(&hugetlb_lock);
> > +
> > +	INIT_LIST_HEAD(folio_list);
> 
> I'm not sure what is the purpose of the reinitialization to list head?
> 

There really is no purpose.  This was copied from
prep_and_add_allocated_folios which also has this unnecessary call.  It is
unnecessary as enqueue_hugetlb_folio() will do a list_move for each
folio on the list.  Therefore, at the end of the loop we KNOW the list
is empty.

I will remove here and in prep_and_add_allocated_folios.

Thanks,
-- 
Mike Kravetz