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

[Hugh Dickins]

On Tue, 13 Nov 2012, Johannes Weiner wrote:
> [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.

Right, yes, I made several fixes there, but never sent out the final
version.  And I can't see your fix to the memcg end of THP migration
either - though I've not done much more than scan the Subjects so far,
I've not yet got to grips with yesterday/today's latest approach.

I'll send out two patches, yours and mine, to what's in the current
linux-next and the current mmotm, which I have been testing with in
several contexts; they probably both apply easily to Ingo's new tree.

But I vehemently hope that this all very soon vanishes from linux-next,
and the new stuff is worked on properly for a while, in a separate
development branch of tip, hopefully converging with Mel's.

Hugh

> 
> 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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