From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Laura Abbott <labbott@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/khugepaged: Convert VM_BUG_ON() to collapse fail
Date: Thu, 15 Mar 2018 16:04:53 -0700 [thread overview]
Message-ID: <20180315160453.dff17cfe3dca056dabc98b9e@linux-foundation.org> (raw)
In-Reply-To: <20180315152353.27989-1-kirill.shutemov@linux.intel.com>
On Thu, 15 Mar 2018 18:23:53 +0300 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
> khugepaged is not yet able to convert PTE-mapped huge pages back to PMD
> mapped. We do not collapse such pages. See check khugepaged_scan_pmd().
>
> But if between khugepaged_scan_pmd() and __collapse_huge_page_isolate()
> somebody managed to instantiate THP in the range and then split the PMD
> back to PTEs we would have a problem -- VM_BUG_ON_PAGE(PageCompound(page))
> will get triggered.
>
> It's possible since we drop mmap_sem during collapse to re-take for
> write.
>
> Replace the VM_BUG_ON() with graceful collapse fail.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: b1caa957ae6d ("khugepaged: ignore pmd tables with THP mapped with ptes")
Jan 2016. Do we need a cc:stable?
next prev parent reply other threads:[~2018-03-15 23:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-15 15:23 Kirill A. Shutemov
2018-03-15 23:04 ` Andrew Morton [this message]
2018-03-16 10:05 ` Kirill A. Shutemov
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