linux-kernel - Re: [PATCH v2 0/7] mm: process_vm_mmap() -- syscall for duplication a process mapping

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Date:   Mon, 3 Jun 2019 17:38:58 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        mhocko@...e.com, keith.busch@...el.com,
        kirill.shutemov@...ux.intel.com, alexander.h.duyck@...ux.intel.com,
        ira.weiny@...el.com, andreyknvl@...gle.com, arunks@...eaurora.org,
        vbabka@...e.cz, cl@...ux.com, riel@...riel.com,
        keescook@...omium.org, hannes@...xchg.org, npiggin@...il.com,
        mathieu.desnoyers@...icios.com, shakeelb@...gle.com, guro@...com,
        aarcange@...hat.com, hughd@...gle.com, jglisse@...hat.com,
        mgorman@...hsingularity.net, daniel.m.jordan@...cle.com,
        jannh@...gle.com, kilobyte@...band.pl, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 0/7] mm: process_vm_mmap() -- syscall for duplication a
 process mapping

On 22.05.2019 18:22, Kirill A. Shutemov wrote:
> On Mon, May 20, 2019 at 05:00:01PM +0300, Kirill Tkhai wrote:
>> This patchset adds a new syscall, which makes possible
>> to clone a VMA from a process to current process.
>> The syscall supplements the functionality provided
>> by process_vm_writev() and process_vm_readv() syscalls,
>> and it may be useful in many situation.
> 
> Kirill, could you explain how the change affects rmap and how it is safe.
> 
> My concern is that the patchset allows to map the same page multiple times
> within one process or even map page allocated by child to the parrent.

Speaking honestly, we already support this model, since ZERO_PAGE() may
be mapped multiply times in any number of mappings.

Kirill