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

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Date:	Mon, 19 Oct 2015 19:01:50 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 0/5] MADV_FREE refactoring and fix KSM page

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);
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