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Date: Sun, 23 Mar 2014 13:26:13 -0700
Message-ID: <CALAqxLVR4PQCZ-UsGhh+486D5PgVVtu3Tk7878zA9oG0yNU_Eg@mail.gmail.com>
Subject: Re: [PATCH 2/5] vrange: Add purged page detection on setting memory non-volatile
From: John Stultz <john.stultz@linaro.org>
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To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Android Kernel Team <kernel-team@android.com>, Johannes Weiner <hannes@cmpxchg.org>, Robert Love <rlove@google.com>, Mel Gorman <mel@csn.ul.ie>, Hugh Dickins <hughd@google.com>, Dave Hansen <dave@sr71.net>, Rik van Riel <riel@redhat.com>, Dmitry Adamushko <dmitry.adamushko@gmail.com>, Neil Brown <neilb@suse.de>, Andrea Arcangeli <aarcange@redhat.com>, Mike Hommey <mh@glandium.org>, Taras Glek <tglek@mozilla.com>, Jan Kara <jack@suse.cz>, Michel Lespinasse <walken@google.com>, Minchan Kim <minchan@kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>

On Sun, Mar 23, 2014 at 10:50 AM, KOSAKI Motohiro
<kosaki.motohiro@gmail.com> wrote:
>> +/**
>> + * 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.

So in the following patch (3/5), we only SIGBUS if the swap entry
is_vpurged_entry()  && the vma is still marked volatile, so this
shouldn't be an issue.

thanks
-john

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