From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
willy@infradead.org, ldufour@linux.vnet.ibm.com,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping
Date: Wed, 11 Jul 2018 13:58:24 +0200 [thread overview]
Message-ID: <20180711115824.GN20050@dhcp22.suse.cz> (raw)
In-Reply-To: <20180711111052.hbyukcwetmjjpij2@kshutemo-mobl1>
On Wed 11-07-18 14:10:52, Kirill A. Shutemov wrote:
[...]
> It's okay. I have another suggestion that also doesn't require VM_DEAD
> trick too :)
>
> 1. Take mmap_sem for write;
> 2. Adjust VMA layout (split/remove). After the step all memory we try to
> unmap is outside any VMA.
> 3. Downgrade mmap_sem to read.
> 4. Zap the page range.
> 5. Drop mmap_sem.
>
> I believe it should be safe.
>
> The pages in the range cannot be re-faulted after step 3 as find_vma()
> will not see the corresponding VMA and deliver SIGSEGV.
>
> New VMAs cannot be created in the range before step 5 since we hold the
> semaphore at least for read the whole time.
>
> Do you see problem in this approach?
Yes this seems to be safe. At least from the first glance.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-07-11 11:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 23:34 Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 1/3] mm: introduce VM_DEAD flag and extend check_stable_address_space to check it Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 2/3] mm: refactor do_munmap() to extract the common part Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 3/3] mm: mmap: zap pages with read mmap_sem for large mapping Yang Shi
2018-07-11 10:33 ` [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap " Michal Hocko
2018-07-11 11:13 ` Kirill A. Shutemov
2018-07-11 11:53 ` Michal Hocko
2018-07-11 17:08 ` Yang Shi
2018-07-11 16:57 ` Yang Shi
2018-07-11 22:49 ` Andrew Morton
2018-07-12 8:15 ` Michal Hocko
2018-07-11 11:10 ` Kirill A. Shutemov
2018-07-11 11:58 ` Michal Hocko [this message]
2018-07-11 17:04 ` Yang Shi
2018-07-12 8:04 ` Michal Hocko
2018-07-12 23:45 ` Yang Shi
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