linux-kernel - Re: [PATCH v5 11/11] mm: memory_hotplug: memory hotremove supports thp migration

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Message-Id: <76fec3ce-986e-406b-6fe1-c785590dc1bd@linux.vnet.ibm.com>
Date:   Fri, 19 May 2017 19:26:27 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Zi Yan <zi.yan@...t.com>, n-horiguchi@...jp.nec.com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, minchan@...nel.org, vbabka@...e.cz,
        mgorman@...hsingularity.net, mhocko@...nel.org,
        khandual@...ux.vnet.ibm.com, zi.yan@...rutgers.edu,
        dnellans@...dia.com
Subject: Re: [PATCH v5 11/11] mm: memory_hotplug: memory hotremove supports
 thp migration

On 04/21/2017 02:17 AM, Zi Yan wrote:
> From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> 
> This patch enables thp migration for memory hotremove.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
> ChangeLog v1->v2:
> - base code switched from alloc_migrate_target to new_node_page()
> ---
>  include/linux/huge_mm.h |  8 ++++++++
>  mm/memory_hotplug.c     | 17 ++++++++++++++---
>  2 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 6f44a2352597..92c2161704c3 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -189,6 +189,13 @@ static inline int hpage_nr_pages(struct page *page)
>  	return 1;
>  }
>  
> +static inline int hpage_order(struct page *page)
> +{
> +	if (unlikely(PageTransHuge(page)))
> +		return HPAGE_PMD_ORDER;
> +	return 0;
> +}
> +

This function seems to be redundant.

>  struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
>  		pmd_t *pmd, int flags);
>  struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
> @@ -233,6 +240,7 @@ static inline bool thp_migration_supported(void)
>  #define HPAGE_PUD_SIZE ({ BUILD_BUG(); 0; })
>  
>  #define hpage_nr_pages(x) 1
> +#define hpage_order(x) 0
>  
>  #define transparent_hugepage_enabled(__vma) 0
>  
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 257166ebdff0..ecae0852994f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1574,6 +1574,7 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  	int nid = page_to_nid(page);
>  	nodemask_t nmask = node_states[N_MEMORY];
>  	struct page *new_page = NULL;
> +	unsigned int order = 0;
>  
>  	/*
>  	 * TODO: allocate a destination hugepage from a nearest neighbor node,
> @@ -1584,6 +1585,11 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  		return alloc_huge_page_node(page_hstate(compound_head(page)),
>  					next_node_in(nid, nmask));
>  
> +	if (thp_migration_supported() && PageTransHuge(page)) {
> +		order = hpage_order(page);

We have already tested the page as THP, we can just use HPAGE_PMD_ORDER.


> +		gfp_mask |= GFP_TRANSHUGE;
> +	}
> +
>  	node_clear(nid, nmask);
>  
>  	if (PageHighMem(page)
> @@ -1591,12 +1597,15 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  		gfp_mask |= __GFP_HIGHMEM;
>  
>  	if (!nodes_empty(nmask))
> -		new_page = __alloc_pages_nodemask(gfp_mask, 0,
> +		new_page = __alloc_pages_nodemask(gfp_mask, order,
>  					node_zonelist(nid, gfp_mask), &nmask);
>  	if (!new_page)
> -		new_page = __alloc_pages(gfp_mask, 0,
> +		new_page = __alloc_pages(gfp_mask, order,
>  					node_zonelist(nid, gfp_mask));
>  
> +	if (new_page && order == hpage_order(page))
> +		prep_transhuge_page(new_page);
> +

new_page has been allocated with 'order' already. I guess just checking
for PageTransHuge(page) on the old THP 'page' should be sufficient as
that has not been changed in any way.