Re: [PATCH 21/31] sched, numa, mm: Implement THP migration

[Johannes Weiner]

[Put Hugh back on CC]

What happened to Hugh's fixes to the LRU handling?  I believe it was
racy beyond affecting memcg, it's just that memcg code had a BUG_ON in
the right place to point it out.

On Tue, Nov 13, 2012 at 06:13:44PM +0100, Ingo Molnar wrote:
> From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> 
> Add THP migration for the NUMA working set scanning fault case.
> 
> It uses the page lock to serialize. No migration pte dance is
> necessary because the pte is already unmapped when we decide
> to migrate.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/n/tip-yv9vbiz2s455zxq1ffzx3fye@xxxxxxxxxxxxxx
> [ Significant fixes and changelog. ]
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
>  mm/huge_memory.c | 131 +++++++++++++++++++++++++++++++++++++++++++------------
>  mm/migrate.c     |   2 +-
>  2 files changed, 103 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c4c0a57..931caf4 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -742,12 +742,13 @@ void do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			   unsigned int flags, pmd_t entry)
>  {
>  	unsigned long haddr = address & HPAGE_PMD_MASK;
> +	struct page *new_page = NULL;
>  	struct page *page = NULL;
> -	int node;
> +	int node, lru;
>  
>  	spin_lock(&mm->page_table_lock);
>  	if (unlikely(!pmd_same(*pmd, entry)))
> -		goto out_unlock;
> +		goto unlock;
>  
>  	if (unlikely(pmd_trans_splitting(entry))) {
>  		spin_unlock(&mm->page_table_lock);
> @@ -755,45 +756,117 @@ void do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  		return;
>  	}
>  
> -#ifdef CONFIG_NUMA
>  	page = pmd_page(entry);
> -	VM_BUG_ON(!PageCompound(page) || !PageHead(page));
> +	if (page) {
> +		VM_BUG_ON(!PageCompound(page) || !PageHead(page));
>  
> -	get_page(page);
> -	spin_unlock(&mm->page_table_lock);
> +		get_page(page);
> +		node = mpol_misplaced(page, vma, haddr);
> +		if (node != -1)
> +			goto migrate;
> +	}
>  
> -	/*
> -	 * XXX should we serialize against split_huge_page ?
> -	 */
> +fixup:
> +	/* change back to regular protection */
> +	entry = pmd_modify(entry, vma->vm_page_prot);
> +	set_pmd_at(mm, haddr, pmd, entry);
> +	update_mmu_cache_pmd(vma, address, entry);
>  
> -	node = mpol_misplaced(page, vma, haddr);
> -	if (node == -1)
> -		goto do_fixup;
> +unlock:
> +	spin_unlock(&mm->page_table_lock);
> +	if (page)
> +		put_page(page);
>  
> -	/*
> -	 * Due to lacking code to migrate thp pages, we'll split
> -	 * (which preserves the special PROT_NONE) and re-take the
> -	 * fault on the normal pages.
> -	 */
> -	split_huge_page(page);
> -	put_page(page);
>  	return;
>  
> -do_fixup:
> +migrate:
> +	spin_unlock(&mm->page_table_lock);
> +
> +	lock_page(page);
>  	spin_lock(&mm->page_table_lock);
> -	if (unlikely(!pmd_same(*pmd, entry)))
> -		goto out_unlock;
> -#endif
> +	if (unlikely(!pmd_same(*pmd, entry))) {
> +		spin_unlock(&mm->page_table_lock);
> +		unlock_page(page);
> +		put_page(page);
> +		return;
> +	}
> +	spin_unlock(&mm->page_table_lock);
>  
> -	/* change back to regular protection */
> -	entry = pmd_modify(entry, vma->vm_page_prot);
> -	if (pmdp_set_access_flags(vma, haddr, pmd, entry, 1))
> -		update_mmu_cache_pmd(vma, address, entry);
> +	new_page = alloc_pages_node(node,
> +	    (GFP_TRANSHUGE | GFP_THISNODE) & ~__GFP_WAIT,
> +	    HPAGE_PMD_ORDER);
>  
> -out_unlock:
> +	if (!new_page)
> +		goto alloc_fail;
> +
> +	lru = PageLRU(page);
> +
> +	if (lru && isolate_lru_page(page)) /* does an implicit get_page() */
> +		goto alloc_fail;
> +
> +	if (!trylock_page(new_page))
> +		BUG();
> +
> +	/* anon mapping, we can simply copy page->mapping to the new page: */
> +	new_page->mapping = page->mapping;
> +	new_page->index = page->index;
> +
> +	migrate_page_copy(new_page, page);
> +
> +	WARN_ON(PageLRU(new_page));
> +
> +	spin_lock(&mm->page_table_lock);
> +	if (unlikely(!pmd_same(*pmd, entry))) {
> +		spin_unlock(&mm->page_table_lock);
> +		if (lru)
> +			putback_lru_page(page);
> +
> +		unlock_page(new_page);
> +		ClearPageActive(new_page);	/* Set by migrate_page_copy() */
> +		new_page->mapping = NULL;
> +		put_page(new_page);		/* Free it */
> +
> +		unlock_page(page);
> +		put_page(page);			/* Drop the local reference */
> +
> +		return;
> +	}
> +
> +	entry = mk_pmd(new_page, vma->vm_page_prot);
> +	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> +	entry = pmd_mkhuge(entry);
> +
> +	page_add_new_anon_rmap(new_page, vma, haddr);
> +
> +	set_pmd_at(mm, haddr, pmd, entry);
> +	update_mmu_cache_pmd(vma, address, entry);
> +	page_remove_rmap(page);
>  	spin_unlock(&mm->page_table_lock);
> -	if (page)
> +
> +	put_page(page);			/* Drop the rmap reference */
> +
> +	if (lru)
> +		put_page(page);		/* drop the LRU isolation reference */
> +
> +	unlock_page(new_page);
> +	unlock_page(page);
> +	put_page(page);			/* Drop the local reference */
> +
> +	return;
> +
> +alloc_fail:
> +	if (new_page)
> +		put_page(new_page);
> +
> +	unlock_page(page);
> +
> +	spin_lock(&mm->page_table_lock);
> +	if (unlikely(!pmd_same(*pmd, entry))) {
>  		put_page(page);
> +		page = NULL;
> +		goto unlock;
> +	}
> +	goto fixup;
>  }
>  
>  int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 3299949..72d1056 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -417,7 +417,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
>   */
>  void migrate_page_copy(struct page *newpage, struct page *page)
>  {
> -	if (PageHuge(page))
> +	if (PageHuge(page) || PageTransHuge(page))
>  		copy_huge_page(newpage, page);
>  	else
>  		copy_highpage(newpage, page);
> -- 
> 1.7.11.7
> 
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