linux-kernel - Re: [PATCH 2/5] vrange: Add purged page detection on setting memory non-volatile

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Date:	Sun, 23 Mar 2014 10:50:06 -0700
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>, Dave Hansen <dave@...1.net>,
	Rik van Riel <riel@...hat.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Neil Brown <neilb@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
	Jan Kara <jack@...e.cz>, Michel Lespinasse <walken@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 2/5] vrange: Add purged page detection on setting memory non-volatile

> +/**
> + * vrange_check_purged_pte - Checks ptes for purged pages
> + *
> + * Iterates over the ptes in the pmd checking if they have
> + * purged swap entries.
> + *
> + * Sets the vrange_walker.pages_purged to 1 if any were purged.
> + */
> +static int vrange_check_purged_pte(pmd_t *pmd, unsigned long addr,
> +                                       unsigned long end, struct mm_walk *walk)
> +{
> +       struct vrange_walker *vw = walk->private;
> +       pte_t *pte;
> +       spinlock_t *ptl;
> +
> +       if (pmd_trans_huge(*pmd))
> +               return 0;
> +       if (pmd_trans_unstable(pmd))
> +               return 0;
> +
> +       pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> +       for (; addr != end; pte++, addr += PAGE_SIZE) {
> +               if (!pte_present(*pte)) {
> +                       swp_entry_t vrange_entry = pte_to_swp_entry(*pte);
> +
> +                       if (unlikely(is_vpurged_entry(vrange_entry))) {
> +                               vw->page_was_purged = 1;
> +                               break;

This function only detect there is vpurge entry or not. But
VRANGE_NONVOLATILE should remove all vpurge entries.
Otherwise, non-volatiled range still makes SIGBUS.

> +                       }
> +               }
> +       }
> +       pte_unmap_unlock(pte - 1, ptl);
> +       cond_resched();
> +
> +       return 0;
> +}
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