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

[Minchan Kim]

On Tue, Oct 20, 2015 at 04:21:09PM +0900, Minchan Kim wrote:
> 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.
> 
> From 104a0940b4c0f97e61de9fee0fd602926ff28312 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@xxxxxxxxxx>
> Date: Tue, 20 Oct 2015 16:00:52 +0900
> Subject: [PATCH] mm: mark head page dirty in split_huge_page
> 
> In thp split in old THP refcount, we mappped all of pages
> (ie, head + tails) to pte_mkdirty and mark PG_flags to every
> tail pages.
> 
> But with THP refcount redesign, we can lose dirty bit in page table
> and PG_dirty for head page if we want to free the THP page using
 
typo.
                                           freeze

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