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[91.12.103.241]) by smtp.gmail.com with ESMTPSA id y1sm10781543wmq.43.2021.08.16.05.30.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Aug 2021 05:30:37 -0700 (PDT) Subject: Re: [private] Re: [RFC PATCH 0/5] madvise MADV_DOEXEC From: David Hildenbrand To: Matthew Wilcox Cc: Khalid Aziz , "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" , Steven Sistare , Anthony Yznaga , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "Gonglei (Arei)" References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <43471cbb-67c6-f189-ef12-0f8302e81b06@oracle.com> <55720e1b39cff0a0f882d8610e7906dc80ea0a01.camel@oracle.com> <86ebdfe4-22ee-9a9a-9d06-8305290d9bc9@redhat.com> Organization: Red Hat Message-ID: Date: Mon, 16 Aug 2021 14:30:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <86ebdfe4-22ee-9a9a-9d06-8305290d9bc9@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 65DF3D00758A Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Z9JVxsWC; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf20.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Rspamd-Server: rspam04 X-Stat-Signature: 1dazx9s8e4n6f66arunkrx5fccrf7wbc X-HE-Tag: 1629117041-905632 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 16.08.21 14:27, David Hildenbrand wrote: > On 16.08.21 14:07, Matthew Wilcox wrote: >> On Mon, Aug 16, 2021 at 10:02:22AM +0200, David Hildenbrand wrote: >>>> Mappings within this address range behave as if they were shared >>>> between threads, so a write to a MAP_PRIVATE mapping will create a >>>> page which is shared between all the sharers. The first process that >>>> declares an address range mshare'd can continue to map objects in the >>>> shared area. All other processes that want mshare'd access to this >>>> memory area can do so by calling mshare(). After this call, the >>>> address range given by mshare becomes a shared range in its address >>>> space. Anonymous mappings will be shared and not COWed. >>> >>> Did I understand correctly that you want to share actual page tables between >>> processes and consequently different MMs? That sounds like a very bad idea. >> >> That is the entire point. Consider a machine with 10,000 instances >> of an application running (process model, not thread model). If each >> application wants to map 1TB of RAM using 2MB pages, that's 4MB of page >> tables per process or 40GB of RAM for the whole machine. > > Note that I am working on asynchronous reclaim of page tables, whereby I > would even reclaim !anonymous page tables under memory pressure. > > Assuming your processes don't touch all memory all the time of course > ... of course, it's a research project and will still require quite some > work because devil is in the detail (locking). > Well, that comment did turn out not-so-private, so it's certainly a good discussion-starter. -- Thanks, David / dhildenb