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From: Oscar Salvador <osalvador@suse.de>
To: Muchun Song <songmuchun@bytedance.com>
Cc: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	peterz@infradead.org, viro@zeniv.linux.org.uk,
	akpm@linux-foundation.org, paulmck@kernel.org,
	mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com,
	rdunlap@infradead.org, oneukum@suse.com,
	anshuman.khandual@arm.com, jroedel@suse.de,
	almasrymina@google.com, rientjes@google.com, willy@infradead.org,
	duanxiongchun@bytedance.com, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 05/19] mm/hugetlb: Introduce pgtable allocation/freeing helpers
Date: Thu, 5 Nov 2020 14:23:41 +0100
Message-ID: <20201105132337.GA7552@linux> (raw)
In-Reply-To: <20201026145114.59424-6-songmuchun@bytedance.com>

On Mon, Oct 26, 2020 at 10:51:00PM +0800, Muchun Song wrote:
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#define VMEMMAP_HPAGE_SHIFT			PMD_SHIFT
> +#define arch_vmemmap_support_huge_mapping()	boot_cpu_has(X86_FEATURE_PSE)

I do not think you need this.
We already have hugepages_supported().

> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#ifndef arch_vmemmap_support_huge_mapping
> +static inline bool arch_vmemmap_support_huge_mapping(void)
> +{
> +	return false;
> +}

Same as above

>  static inline unsigned int nr_free_vmemmap(struct hstate *h)
>  {
>  	return h->nr_free_vmemmap_pages;
>  }
>  
> +static inline unsigned int nr_vmemmap(struct hstate *h)
> +{
> +	return nr_free_vmemmap(h) + RESERVE_VMEMMAP_NR;
> +}
> +
> +static inline unsigned long nr_vmemmap_size(struct hstate *h)
> +{
> +	return (unsigned long)nr_vmemmap(h) << PAGE_SHIFT;
> +}
> +
> +static inline unsigned int nr_pgtable(struct hstate *h)
> +{
> +	unsigned long vmemmap_size = nr_vmemmap_size(h);
> +
> +	if (!arch_vmemmap_support_huge_mapping())
> +		return 0;
> +
> +	/*
> +	 * No need pre-allocate page tabels when there is no vmemmap pages
> +	 * to free.
> +	 */
> +	if (!nr_free_vmemmap(h))
> +		return 0;
> +
> +	return ALIGN(vmemmap_size, VMEMMAP_HPAGE_SIZE) >> VMEMMAP_HPAGE_SHIFT;
> +}

IMHO, Mike's naming suggestion fit much better.

> +static void vmemmap_pgtable_deposit(struct page *page, pte_t *pte_p)
> +{
> +	pgtable_t pgtable = virt_to_page(pte_p);
> +
> +	/* FIFO */
> +	if (!page_huge_pte(page))
> +		INIT_LIST_HEAD(&pgtable->lru);
> +	else
> +		list_add(&pgtable->lru, &page_huge_pte(page)->lru);
> +	page_huge_pte(page) = pgtable;
> +}

I think it would make more sense if this took a pgtable argument
instead of a pte_t *.

> +static pte_t *vmemmap_pgtable_withdraw(struct page *page)
> +{
> +	pgtable_t pgtable;
> +
> +	/* FIFO */
> +	pgtable = page_huge_pte(page);
> +	if (unlikely(!pgtable))
> +		return NULL;

AFAICS, above check only needs to be run once.
It think we can move it to vmemmap_pgtable_free, can't we?

> +	page_huge_pte(page) = list_first_entry_or_null(&pgtable->lru,
> +						       struct page, lru);
> +	if (page_huge_pte(page))
> +		list_del(&pgtable->lru);
> +	return page_to_virt(pgtable);
> +}

At the risk of adding more code, I think it would be nice to return a
pagetable_t?
So it is more coherent with the name of the function and with what
we are doing.

It is a pitty we cannot converge these and pgtable_trans_huge_*.
They share some code but it is different enough.

> +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> +	int i;
> +	pte_t *pte_p;
> +	unsigned int nr = nr_pgtable(h);
> +
> +	if (!nr)
> +		return 0;
> +
> +	vmemmap_pgtable_init(page);

Maybe just open code this one?

> +static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
> +{
> +	pte_t *pte_p;
> +
> +	if (!nr_pgtable(h))
> +		return;
> +
> +	while ((pte_p = vmemmap_pgtable_withdraw(page)))
> +		pte_free_kernel(&init_mm, pte_p);

As mentioned above, move the pgtable_t check from vmemmap_pgtable_withdraw
in here.

  
>  static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>  {
> +	/* Must be called before the initialization of @page->lru */
> +	vmemmap_pgtable_free(h, page);
> +
>  	INIT_LIST_HEAD(&page->lru);
>  	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
>  	set_hugetlb_cgroup(page, NULL);
> @@ -1783,6 +1892,14 @@ static struct page *alloc_fresh_huge_page(struct hstate *h,
>  	if (!page)
>  		return NULL;
>  
> +	if (vmemmap_pgtable_prealloc(h, page)) {
> +		if (hstate_is_gigantic(h))
> +			free_gigantic_page(page, huge_page_order(h));
> +		else
> +			put_page(page);
> +		return NULL;
> +	}
> +

I must confess I am bit puzzled.

IIUC, in this patch we are just adding the helpers to create/tear the page
tables.
I do not think we actually need to call vmemmap_pgtable_prealloc/vmemmap_pgtable_free, do we?
In the end, we are just allocating pages for pagetables and then free them shortly.

I think it would make more sense to add the calls when they need to be?


-- 
Oscar Salvador
SUSE L3

  parent reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 14:50 [PATCH v2 00/19] Free some vmemmap pages of hugetlb page Muchun Song
2020-10-26 14:50 ` [PATCH v2 01/19] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
2020-10-26 14:50 ` [PATCH v2 02/19] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
2020-10-26 14:50 ` [PATCH v2 03/19] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-10-29 10:29   ` Oscar Salvador
2020-10-29 13:34     ` [External] " Muchun Song
2020-10-26 14:50 ` [PATCH v2 04/19] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-10-27 22:03   ` Mike Kravetz
2020-10-29 13:26   ` Oscar Salvador
2020-10-29 13:41     ` [External] " Muchun Song
2020-10-26 14:51 ` [PATCH v2 05/19] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
2020-10-28  0:32   ` Mike Kravetz
2020-10-28  7:26     ` [External] " Muchun Song
2020-10-28 23:42       ` Mike Kravetz
2020-11-05 13:23   ` Oscar Salvador [this message]
2020-11-05 16:08     ` Muchun Song
2020-11-06  9:46       ` Oscar Salvador
2020-11-06 16:43         ` Muchun Song
2020-10-26 14:51 ` [PATCH v2 06/19] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
2020-10-26 14:51 ` [PATCH v2 07/19] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
2020-10-26 16:01   ` Matthew Wilcox
2020-10-27  2:58     ` [External] " Muchun Song
2020-10-28 23:42   ` Mike Kravetz
2020-10-29  6:13     ` [External] " Muchun Song
2020-10-29 21:59       ` Mike Kravetz
2020-10-30  2:58         ` Muchun Song
2020-10-26 14:51 ` [PATCH v2 08/19] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
2020-10-26 14:51 ` [PATCH v2 09/19] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
2020-10-26 14:51 ` [PATCH v2 10/19] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
2020-10-26 14:51 ` [PATCH v2 11/19] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
2020-10-26 14:51 ` [PATCH v2 12/19] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
2020-10-26 14:51 ` [PATCH v2 13/19] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
2020-10-26 14:51 ` [PATCH v2 14/19] mm/hugetlb: Clear PageHWPoison on the non-error memory page Muchun Song
2020-10-26 14:51 ` [PATCH v2 15/19] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-10-26 14:51 ` [PATCH v2 16/19] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-10-26 14:51 ` [PATCH v2 17/19] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
2020-10-26 14:51 ` [PATCH v2 18/19] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-10-26 14:51 ` [PATCH v2 19/19] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
2020-10-26 15:53 ` [PATCH v2 00/19] Free some vmemmap pages of hugetlb page Matthew Wilcox
2020-10-27  2:54   ` [External] " Muchun Song
2020-10-30  9:14 ` Michal Hocko
2020-10-30 10:24   ` [External] " Muchun Song
2020-10-30 15:19     ` Michal Hocko

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