linux-kernel - Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb

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Message-ID: <CAHGf_=ruv9itn7fhcL=Ar7z_6wQ5Ga_4kj7Ui3EfDUe_cV7D0w@mail.gmail.com>
Date:	Mon, 8 Apr 2013 16:57:44 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb_page()

> -               if (absent ||
> +               /*
> +                * is_swap_pte test covers both is_hugetlb_entry_hwpoisoned
> +                * and hugepages under migration in which case
> +                * hugetlb_fault waits for the migration and bails out
> +                * properly for HWPosined pages.
> +                */
> +               if (absent || is_swap_pte(huge_ptep_get(pte)) ||
>                     ((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) {
>                         int ret;

Your comment describe what the code is. However we want the comment describe
why. In migration case, calling hugetlb_fault() is natural. but in
hwpoison case, it is
needed more explanation. Why can't we call is_hugetlb_hwpoisoned() directly?
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