From: Mel Gorman <mgorman@techsingularity.net>
To: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Rik van Riel <riel@redhat.com>, Michal Hocko <mhocko@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, numa: Fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa
Date: Mon, 10 Apr 2017 19:07:14 +0100 [thread overview]
Message-ID: <20170410180714.7yfnxl7qin72jcob@techsingularity.net> (raw)
In-Reply-To: <8A6309F4-DB76-48FA-BE7F-BF9536A4C4E5@cs.rutgers.edu>
On Mon, Apr 10, 2017 at 12:49:40PM -0500, Zi Yan wrote:
> On 10 Apr 2017, at 12:20, Mel Gorman wrote:
>
> > On Mon, Apr 10, 2017 at 11:45:08AM -0500, Zi Yan wrote:
> >>> While this could be fixed with heavy locking, it's only necessary to
> >>> make a copy of the PMD on the stack during change_pmd_range and avoid
> >>> races. A new helper is created for this as the check if quite subtle and the
> >>> existing similar helpful is not suitable. This passed 154 hours of testing
> >>> (usually triggers between 20 minutes and 24 hours) without detecting bad
> >>> PMDs or corruption. A basic test of an autonuma-intensive workload showed
> >>> no significant change in behaviour.
> >>>
> >>> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> >>> Cc: stable@vger.kernel.org
> >>
> >> Does this patch fix the same problem fixed by Kirill's patch here?
> >> https://lkml.org/lkml/2017/3/2/347
> >>
> >
> > I don't think so. The race I'm concerned with is due to locks not being
> > held and is in a different path.
>
> I do not agree. Kirill's patch is fixing the same race problem but in
> zap_pmd_range().
>
> The original autoNUMA code first clears PMD then sets it to protnone entry.
> pmd_trans_huge() does not return TRUE because it saw cleared PMD, but
> pmd_none_or_clear_bad() later saw the protnone entry and reported it as bad.
> Is this the problem you are trying solve?
>
> Kirill's patch will pmdp_invalidate() the PMD entry, which keeps _PAGE_PSE bit,
> so pmd_trans_huge() will return TRUE. In this case, it also fixes
> your race problem in change_pmd_range().
>
> Let me know if I miss anything.
>
Ok, now I see. I think you're correct and I withdraw the patch.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2017-04-10 18:07 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-10 9:48 [PATCH] mm, numa: Fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa Mel Gorman
2017-04-10 10:03 ` Vlastimil Babka
2017-04-10 12:19 ` Mel Gorman
2017-04-10 12:38 ` Rik van Riel
2017-04-10 13:53 ` Michal Hocko
2017-04-10 17:38 ` Mel Gorman
2017-04-10 16:45 ` Zi Yan
2017-04-10 17:20 ` Mel Gorman
2017-04-10 17:49 ` Zi Yan
2017-04-10 18:07 ` Mel Gorman [this message]
2017-04-10 22:09 ` Andrew Morton
2017-04-10 22:28 ` Zi Yan
2017-04-11 6:35 ` Vlastimil Babka
2017-04-11 21:44 ` Andrew Morton
2017-04-11 8:29 ` Mel Gorman
2020-02-16 19:18 [PATCH] mm, numa: fix " Rafael Aquini
2020-02-16 23:32 ` Mel Gorman
2020-03-07 2:40 ` Qian Cai
2020-03-07 3:05 ` Rafael Aquini
2020-03-08 3:20 ` Qian Cai
2020-03-08 23:14 ` Rafael Aquini
2020-03-09 3:27 ` Qian Cai
2020-03-09 15:05 ` Rafael Aquini
2020-03-11 0:04 ` Qian Cai
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