From: Yang Shi <yang.shi@linux.alibaba.com>
To: Peter Zijlstra <peterz@infradead.org>
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 18:03:34 -0700 [thread overview]
Message-ID: <e54e298d-ef86-19a7-6f6b-07776f9a43e2@linux.alibaba.com> (raw)
In-Reply-To: <20180626074344.GZ2458@hirez.programming.kicks-ass.net>
On 6/26/18 12:43 AM, Peter Zijlstra wrote:
> 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.
Thanks, Peter. Yes, by looking the code and trying two different
approaches, it looks this approach is the most straight-forward one.
Splitting vma up-front can save a lot pain later. Holding write mmap_sem
for this job before zapping mappings sounds worth the cost (very short
write critical section).
And, VM_DEAD can be set exclusively with write mmap_sem without racing
with page faults, this will give us consistent behavior for the race
between PF and munmap. And, we don't need care about overlapped vma
since it has been split before.
Yang
next prev parent reply other threads:[~2018-06-27 1:03 UTC|newest]
Thread overview: 26+ 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 ` [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
[not found] ` <158a4e4c-d290-77c4-a595-71332ede392b@linux.alibaba.com>
2018-06-20 0:31 ` Nadav Amit
2018-06-20 7:18 ` Michal Hocko
2018-06-20 17:12 ` Nadav Amit
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 7:43 ` Peter Zijlstra
2018-06-27 1:03 ` Yang Shi [this message]
2018-06-27 7:24 ` Michal Hocko
2018-06-27 17:23 ` Yang Shi
2018-06-28 11:51 ` Michal Hocko
2018-06-28 19:10 ` Yang Shi
2018-06-29 0:59 ` Yang Shi
2018-06-29 11:39 ` Michal Hocko
2018-06-29 16:50 ` Yang Shi
2018-06-29 11:34 ` Michal Hocko
2018-06-29 16:45 ` Yang Shi
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