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From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
To: Matthew Wilcox <willy@infradead.org>,
	Yang Shi <yang.shi@linux.alibaba.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/8] mm: mmap: unmap large mapping by section
Date: Thu, 22 Mar 2018 16:32:00 +0100	[thread overview]
Message-ID: <18a727fd-f006-9fae-d9ca-74b9004f0a8b@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180321224631.GB3969@bombadil.infradead.org>



On 21/03/2018 23:46, Matthew Wilcox wrote:
> On Wed, Mar 21, 2018 at 02:45:44PM -0700, Yang Shi wrote:
>> Marking vma as deleted sounds good. The problem for my current approach is
>> the concurrent page fault may succeed if it access the not yet unmapped
>> section. Marking deleted vma could tell page fault the vma is not valid
>> anymore, then return SIGSEGV.
>>
>>> does not care; munmap will need to wait for the existing munmap operation
>>
>> Why mmap doesn't care? How about MAP_FIXED? It may fail unexpectedly, right?
> 
> The other thing about MAP_FIXED that we'll need to handle is unmapping
> conflicts atomically.  Say a program has a 200GB mapping and then
> mmap(MAP_FIXED) another 200GB region on top of it.  So I think page faults
> are also going to have to wait for deleted vmas (then retry the fault)
> rather than immediately raising SIGSEGV.

Regarding the page fault, why not relying on the PTE locking ?

When munmap() will unset the PTE it will have to held the PTE lock, so this
will serialize the access.
If the page fault occurs before the mmap(MAP_FIXED), the page mapped will be
removed when mmap(MAP_FIXED) would do the cleanup. Fair enough.

  reply	other threads:[~2018-03-22 15:32 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-20 21:31 [RFC PATCH 0/8] Drop mmap_sem during unmapping large map Yang Shi
2018-03-20 21:31 ` [RFC PATCH 1/8] mm: mmap: unmap large mapping by section Yang Shi
2018-03-21 13:08   ` Michal Hocko
2018-03-21 16:31     ` Yang Shi
2018-03-21 17:29       ` Matthew Wilcox
2018-03-21 21:45         ` Yang Shi
2018-03-21 22:15           ` Matthew Wilcox
2018-03-21 22:40             ` Yang Shi
2018-03-21 22:46           ` Matthew Wilcox
2018-03-22 15:32             ` Laurent Dufour [this message]
2018-03-22 15:40               ` Matthew Wilcox
2018-03-22 15:54                 ` Laurent Dufour
2018-03-22 16:05                   ` Matthew Wilcox
2018-03-22 16:18                     ` Laurent Dufour
2018-03-22 16:46                       ` Yang Shi
2018-03-23 13:03                         ` Laurent Dufour
2018-03-22 16:51                       ` Matthew Wilcox
2018-03-22 16:49                     ` Yang Shi
2018-03-22 17:34         ` Yang Shi
2018-03-22 18:48           ` Matthew Wilcox
2018-03-24 18:24         ` Jerome Glisse
2018-03-21 13:14   ` Michal Hocko
2018-03-21 16:50     ` Yang Shi
2018-03-21 17:16       ` Yang Shi
2018-03-21 21:23         ` Michal Hocko
2018-03-21 22:36           ` Yang Shi
2018-03-22  9:10             ` Michal Hocko
2018-03-22 16:06               ` Yang Shi
2018-03-22 16:12                 ` Michal Hocko
2018-03-22 16:13                 ` Matthew Wilcox
2018-03-22 16:28                   ` Laurent Dufour
2018-03-22 16:36                     ` David Laight
2018-03-20 21:31 ` [RFC PATCH 2/8] mm: mmap: pass atomic parameter to do_munmap() call sites Yang Shi
2018-03-20 21:31 ` [RFC PATCH 3/8] mm: mremap: pass atomic parameter to do_munmap() Yang Shi
2018-03-20 21:31 ` [RFC PATCH 4/8] mm: nommu: add " Yang Shi
2018-03-20 21:31 ` [RFC PATCH 5/8] ipc: shm: pass " Yang Shi
2018-03-20 21:31 ` [RFC PATCH 6/8] fs: proc/vmcore: " Yang Shi
2018-03-20 21:31 ` [RFC PATCH 7/8] x86: mpx: " Yang Shi
2018-03-20 22:35   ` Thomas Gleixner
2018-03-21 16:53     ` Yang Shi
2018-03-20 21:31 ` [RFC PATCH 8/8] x86: vma: " Yang Shi

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