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Date: Sat, 29 Jul 2023 09:37:21 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Usama Arif <usama.arif@...edance.com>
Cc: linux-mm@...ck.org, muchun.song@...ux.dev, mike.kravetz@...cle.com,
linux-kernel@...r.kernel.org, fam.zheng@...edance.com,
liangma@...ngbit.com, simon.evans@...edance.com,
punit.agrawal@...edance.com
Subject: Re: [v1 1/6] mm: hugetlb: Skip prep of tail pages when HVO is enabled
On Thu, Jul 27, 2023 at 09:46:19PM +0100, Usama Arif wrote:
> When vmemmap is optimizable, it will free all the
> duplicated tail pages in hugetlb_vmemmap_optimize while
> preparing the new hugepage. Hence, there is no need to
> prepare them.
>
> For 1G x86 hugepages, it avoids preparing
> 262144 - 64 = 262080 struct pages per hugepage.
>
> Signed-off-by: Usama Arif <usama.arif@...edance.com>
> ---
> mm/hugetlb.c | 32 +++++++++++++++++++++++---------
> mm/hugetlb_vmemmap.c | 2 +-
> mm/hugetlb_vmemmap.h | 7 +++++++
> 3 files changed, 31 insertions(+), 10 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 64a3239b6407..58cf5978bee1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1943,13 +1943,24 @@ static void prep_new_hugetlb_folio(struct hstate *h, struct folio *folio, int ni
> }
>
> static bool __prep_compound_gigantic_folio(struct folio *folio,
> - unsigned int order, bool demote)
> + unsigned int order, bool demote,
> + bool hvo)
I think it would be cleaner to pass struct hstate * instead of order here
so that order and hvo can be computed locally.
> {
> int i, j;
> int nr_pages = 1 << order;
> struct page *p;
>
> __folio_clear_reserved(folio);
> +
> +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> + /*
> + * No need to prep pages that will be freed later by hugetlb_vmemmap_optimize
> + * in prep_new_huge_page. Hence, reduce nr_pages to the pages that will be kept.
> + */
> + if (hvo)
if (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && hvo)
is better than ifdef IMO.
> + nr_pages = HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page);
> +#endif
> +
> for (i = 0; i < nr_pages; i++) {
> p = folio_page(folio, i);
>
> @@ -2020,15 +2031,15 @@ static bool __prep_compound_gigantic_folio(struct folio *folio,
> }
>
> static bool prep_compound_gigantic_folio(struct folio *folio,
> - unsigned int order)
> + unsigned int order, bool hvo)
> {
> - return __prep_compound_gigantic_folio(folio, order, false);
> + return __prep_compound_gigantic_folio(folio, order, false, hvo);
> }
>
> static bool prep_compound_gigantic_folio_for_demote(struct folio *folio,
> - unsigned int order)
> + unsigned int order, bool hvo)
> {
> - return __prep_compound_gigantic_folio(folio, order, true);
> + return __prep_compound_gigantic_folio(folio, order, true, hvo);
> }
>
> /*
> @@ -2185,7 +2196,8 @@ static struct folio *alloc_fresh_hugetlb_folio(struct hstate *h,
> if (!folio)
> return NULL;
> if (hstate_is_gigantic(h)) {
> - if (!prep_compound_gigantic_folio(folio, huge_page_order(h))) {
> + if (!prep_compound_gigantic_folio(folio, huge_page_order(h),
> + vmemmap_should_optimize(h, &folio->page))) {
> /*
> * Rare failure to convert pages to compound page.
> * Free pages and try again - ONCE!
> @@ -3201,7 +3213,8 @@ static void __init gather_bootmem_prealloc(void)
>
> VM_BUG_ON(!hstate_is_gigantic(h));
> WARN_ON(folio_ref_count(folio) != 1);
> - if (prep_compound_gigantic_folio(folio, huge_page_order(h))) {
> + if (prep_compound_gigantic_folio(folio, huge_page_order(h),
> + vmemmap_should_optimize(h, page))) {
> WARN_ON(folio_test_reserved(folio));
> prep_new_hugetlb_folio(h, folio, folio_nid(folio));
> free_huge_page(page); /* add to the hugepage allocator */
> @@ -3624,8 +3637,9 @@ static int demote_free_hugetlb_folio(struct hstate *h, struct folio *folio)
> subpage = folio_page(folio, i);
> inner_folio = page_folio(subpage);
> if (hstate_is_gigantic(target_hstate))
> - prep_compound_gigantic_folio_for_demote(inner_folio,
> - target_hstate->order);
> + prep_compound_gigantic_folio_for_demote(folio,
> + target_hstate->order,
> + vmemmap_should_optimize(target_hstate, subpage));
> else
> prep_compound_page(subpage, target_hstate->order);
> folio_change_private(inner_folio, NULL);
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index c2007ef5e9b0..b721e87de2b3 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -486,7 +486,7 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
> }
>
> /* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
> -static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
> +bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
> {
> if (!READ_ONCE(vmemmap_optimize_enabled))
> return false;
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 25bd0e002431..07555d2dc0cb 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -13,6 +13,7 @@
> #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head);
> void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head);
> +bool vmemmap_should_optimize(const struct hstate *h, const struct page *head);
>
> /*
> * Reserve one vmemmap page, all vmemmap addresses are mapped to it. See
> @@ -51,6 +52,12 @@ static inline unsigned int hugetlb_vmemmap_optimizable_size(const struct hstate
> {
> return 0;
> }
> +
> +bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
> +{
> + return false;
> +}
> +
> #endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
>
> static inline bool hugetlb_vmemmap_optimizable(const struct hstate *h)
> --
> 2.25.1
>
--
Sincerely yours,
Mike.
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