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From: Peter Zijlstra <peterz@infradead.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	Nadav Amit <nadav.amit@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	ldufour@linux.vnet.ibm.com,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	acme@kernel.org, alexander.shishkin@linux.intel.com,
	jolsa@redhat.com, namhyung@kernel.org,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping
Date: Tue, 26 Jun 2018 09:43:44 +0200	[thread overview]
Message-ID: <20180626074344.GZ2458@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <263935d9-d07c-ab3e-9e42-89f73f57be1e@linux.alibaba.com>

On Mon, Jun 25, 2018 at 05:06:23PM -0700, Yang Shi wrote:
> By looking this deeper, we may not be able to cover all the unmapping range
> for VM_DEAD, for example, if the start addr is in the middle of a vma. We
> can't set VM_DEAD to that vma since that would trigger SIGSEGV for still
> mapped area.
> 
> splitting can't be done with read mmap_sem held, so maybe just set VM_DEAD
> to non-overlapped vmas. Access to overlapped vmas (first and last) will
> still have undefined behavior.

Acquire mmap_sem for writing, split, mark VM_DEAD, drop mmap_sem. Acquire
mmap_sem for reading, madv_free drop mmap_sem. Acquire mmap_sem for
writing, free everything left, drop mmap_sem.

?

Sure, you acquire the lock 3 times, but both write instances should be
'short', and I suppose you can do a demote between 1 and 2 if you care.

  reply	other threads:[~2018-06-26  7:43 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-18 23:34 [RFC v2 0/2] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-06-18 23:34 ` Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 1/2] uprobes: make vma_has_uprobes non-static Yang Shi
2018-06-18 23:34 ` [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping Yang Shi
2018-06-19 10:02   ` Peter Zijlstra
2018-06-19 21:13     ` Yang Shi
2018-06-20  7:17       ` Michal Hocko
2018-06-20 16:23         ` Yang Shi
2018-06-19 22:17   ` Nadav Amit
2018-06-19 23:08     ` Yang Shi
2018-06-20  0:31       ` Nadav Amit
2018-06-20  7:18         ` Michal Hocko
2018-06-20  7:18           ` Michal Hocko
2018-06-20 17:12           ` Nadav Amit
2018-06-20 18:42           ` Yang Shi
2018-06-20 18:42             ` Yang Shi
2018-06-23  1:01             ` Yang Shi
2018-06-25  9:14               ` Michal Hocko
2018-06-26  0:06           ` Yang Shi
2018-06-26  0:06             ` Yang Shi
2018-06-26  7:43             ` Peter Zijlstra [this message]
2018-06-27  1:03               ` Yang Shi
2018-06-27  7:24                 ` Michal Hocko
2018-06-27 17:23                   ` Yang Shi
2018-06-27 17:23                     ` Yang Shi
2018-06-28 11:51                     ` Michal Hocko
2018-06-28 11:51                       ` Michal Hocko
2018-06-28 19:10                       ` Yang Shi
2018-06-28 19:10                         ` Yang Shi
2018-06-29  0:59                         ` Yang Shi
2018-06-29  0:59                           ` Yang Shi
2018-06-29 11:39                           ` Michal Hocko
2018-06-29 11:39                             ` Michal Hocko
2018-06-29 16:50                             ` Yang Shi
2018-06-29 16:50                               ` Yang Shi
2018-06-29 11:34                         ` Michal Hocko
2018-06-29 11:34                           ` Michal Hocko
2018-06-29 16:45                           ` Yang Shi
2018-06-29 16:45                             ` Yang Shi

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