Re: [PATCH 0/5] MADV_FREE refactoring and fix KSM page

[Minchan Kim]

On Mon, Oct 19, 2015 at 07:01:50PM +0900, Minchan Kim wrote:
> On Mon, Oct 19, 2015 at 03:31:42PM +0900, Minchan Kim wrote:
> > Hello, it's too late since I sent previos patch.
> > https://lkml.org/lkml/2015/6/3/37
> > 
> > This patch is alomost new compared to previos approach.
> > I think this is more simple, clear and easy to review.
> > 
> > One thing I should notice is that I have tested this patch
> > and couldn't find any critical problem so I rebased patchset
> > onto recent mmotm(ie, mmotm-2015-10-15-15-20) to send formal
> > patchset. Unfortunately, I start to see sudden discarding of
> > the page we shouldn't do. IOW, application's valid anonymous page
> > was disappeared suddenly.
> > 
> > When I look through THP changes, I think we could lose
> > dirty bit of pte between freeze_page and unfreeze_page
> > when we mark it as migration entry and restore it.
> > So, I added below simple code without enough considering
> > and cannot see the problem any more.
> > I hope it's good hint to find right fix this problem.
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index d5ea516ffb54..e881c04f5950 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -3138,6 +3138,9 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
> >  		if (is_write_migration_entry(swp_entry))
> >  			entry = maybe_mkwrite(entry, vma);
> >  
> > +		if (PageDirty(page))
> > +			SetPageDirty(page);
> 
> The condition of PageDirty was typo. I didn't add the condition.
> Just added.
> 
>                 SetPageDirty(page);

I reviewed THP refcount redesign patch and It seems below patch fixes
MADV_FREE problem. It works well for hours.