linux-kernel - Re: [PATCH 3/4] thp: fix split vs. unmap race

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Date:	Wed, 04 Nov 2015 17:20:15 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Andrea Arcangeli" <aarcange@...hat.com>,
	"Hugh Dickins" <hughd@...gle.com>,
	"Naoya Horiguchi" <n-horiguchi@...jp.nec.com>,
	"Sasha Levin" <sasha.levin@...cle.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, "'Minchan Kim'" <minchan@...nel.org>
Subject: Re: [PATCH 3/4] thp: fix split vs. unmap race

> @@ -1135,20 +1135,12 @@ void do_page_add_anon_rmap(struct page *page,
>  	bool compound = flags & RMAP_COMPOUND;
>  	bool first;
> 
> -	if (PageTransCompound(page)) {
> +	if (compound) {
> +		atomic_t *mapcount;
>  		VM_BUG_ON_PAGE(!PageLocked(page), page);
> -		if (compound) {
> -			atomic_t *mapcount;
> -
> -			VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> -			mapcount = compound_mapcount_ptr(page);
> -			first = atomic_inc_and_test(mapcount);
> -		} else {
> -			/* Anon THP always mapped first with PMD */
> -			first = 0;
> -			VM_BUG_ON_PAGE(!page_mapcount(page), page);
> -			atomic_inc(&page->_mapcount);
> -		}
> +		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
> +		mapcount = compound_mapcount_ptr(page);
> +		first = atomic_inc_and_test(mapcount);
>  	} else {
>  		VM_BUG_ON_PAGE(compound, page);

Then this debug info is no longer needed.
>  		first = atomic_inc_and_test(&page->_mapcount);


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