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s=mail; t=1677770056; bh=CcEqHND5mbOVDN70lUAK9blEjv5boHx15r9OKCOPiBw=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=hVqkMEDQ84QHoJNQe0kTCcPHsKDUFpk/1SRmYQtPjbYFeM94fajVPlOX8Fu6LNnv7 8hZR7OjZlrl5f7U86WL08LhzXM+aINLLCotPxs0eL+j2m6rbq853KKLCf9kZP08+y7 f9tG/h58lU7IcmNXyl9t84lK7PMdRJ8OwJlSANzkWvQ/c1MTz1+PnNvSnM5OjDQmSA 62vNnWRNHk+/5eDMMqTUKhrl4s9XenOqEyQA4p3DlUJ8f26jmte/KmZONQAwUpG1Bg 2LNyKZJSq0aMCYYPt4JRqORGUz8okXNFydnyI8PTuTx1OY56Flp2Y2ry5ncD9GI9FK a+VbBmjF1RXpg== Message-ID: Date: Thu, 2 Mar 2023 20:14:05 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Cc: Muhammad Usama Anjum , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Mike Rapoport , Axel Rasmussen , Nadav Amit , "kernel@collabora.com" Subject: Re: [PATCH v2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED To: David Hildenbrand , Peter Xu References: <20230227230044.1596744-1-peterx@redhat.com> <640319be-ddb6-d74f-b731-eee5ceab3d01@collabora.com> <8783f47e-76ea-cd24-e373-f2156884cd05@redhat.com> <982c1623-ac28-2743-d6a3-4faf42f72d47@redhat.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: <982c1623-ac28-2743-d6a3-4faf42f72d47@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 79045C0011 X-Stat-Signature: k564g7k9ic8kqcm8sz5qxw49drhzzi3f X-HE-Tag: 1677770057-299635 X-HE-Meta: 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 xuFiy+ZU efWDPDCjoJ4L7TjaJceHA6cLRaNw0cxcRRW8HQDBEXsj95gGH6IrOEurEMYulfhptbMGVfMKw/GPHLWuv/dCScH8iVUATYx6dWDdzSzXAZ2nZSuhtXF5ogm9IoOkQ1XBOa5NK/PygJCZHGecK8r+ZRTyDeORL1BoaIVzedqGXKD47esmqdR7+ONfS7exGXF+mDOhLlmMX4FZIJ4aHrCr1h9payP6twJ/8jA4Qn254tMPBU6ikOS3NbXtx4tU6RIj7M0WQvEOpfXTYq6pSfFPO2X+kBEfNzH7ySrsJXqmbZRVmfEO5Qbk6EP7+bBGTl4EDgkvFu7l6/30D19GU0sc4S0U4p392RZ2IgV8nSJaPmgH5qtfpUKL3lMzGeGbHscUhY9Nm X-Bogosity: Ham, tests=bogofilter, spamicity=0.000008, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/2/23 7:01 PM, David Hildenbrand wrote: > On 02.03.23 14:57, Peter Xu wrote: >> On Thu, Mar 02, 2023 at 10:37:44AM +0100, David Hildenbrand wrote: >>> Especially for such large sparse VMAs, the current way of allocating >>> pagetables to place markers/zeropages is far from optimal. >> >> IMHO that's not a generic workload.  As mentioned in the reply there, I >> would suggest we go with simple then we have space to optimize it in the >> future if necessary, because the API will be the same. This is a good idea. I'm trying to understand why aren't we going with most optimized implementation. Why aren't we targeting it at this point in time? >> > > I disagree with "generic workload", we use sparse mmaps all over the place, > and when blindly used by e.g., CRIU, we'll simply end up wasting memory and > time. I've heard about a use case where a file of size 10s of GBs can be mapped to the memory and then accessed off and on. We need to handle this correctly and efficiently. > > But I already agreed that this optimization that is a separate thing to > implement. > -- BR, Muhammad Usama Anjum