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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id w65-20020a623044000000b0056c349f5c70sm22529550pfw.79.2023.01.18.13.51.41 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 18 Jan 2023 13:51:42 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3731.300.101.1.3\)) Subject: Re: [PATCH 3/3] mm/uffd: Detect pgtable allocation failures From: Nadav Amit In-Reply-To: Date: Wed, 18 Jan 2023 13:51:30 -0800 Cc: David Hildenbrand , Linux-MM , kernel list , Mike Kravetz , Muchun Song , Andrea Arcangeli , James Houghton , Axel Rasmussen , Andrew Morton Content-Transfer-Encoding: quoted-printable Message-Id: <832F027A-3778-4670-BED6-1222FA905F13@gmail.com> References: <20230104225207.1066932-1-peterx@redhat.com> <20230104225207.1066932-4-peterx@redhat.com> To: Peter Xu X-Mailer: Apple Mail (2.3731.300.101.1.3) X-Rspam-User: X-Rspamd-Queue-Id: 6DEE2140017 X-Rspamd-Server: rspam01 X-Stat-Signature: tzqk5jp9jquh84cyikrskui7htfidsre X-HE-Tag: 1674078704-639464 X-HE-Meta: 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 Kx+aXj/a AuXFBoXbYnnKCrxeWnVwn0dhFlcnQAJle5EaPfURf+gJQixJMbmjHSQHOax1mnfATDGUdPoSFFluhIm6zXVZM4TzH6guxUhIp/Dsq+TpfbSwmzLI3trzzU+zmMX3/w6KMcVSDbh+rGrkvHtsSA3BN0fAW7w== 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: Sorry for the late response. >> Yes, I propose it as an optional flag for UFFD-WP. >> Anyhow, I believe the UFFD-WP as implemented now is not efficient and >> should=E2=80=99ve been vectored to allow one TLB shootdown for many >> non-consecutive pages. >=20 > Agreed. Would providing a vector of ranges help too for a few uffd = ioctls? >=20 > I'm also curious whether you're still actively developing (or running) = your > iouring series. So I finished building a prototype some time ago, and one of the = benefits was in reducing memory reclamation time. Unfortunately, MGLRU then came = and took away a lot of the benefit. A colleague of mine had a slightly different use-case, so I gave him the code and he showed interest in upstreaming it. After some probing, it = turns out he decided he is not into the effort of upstreaming it. I can = upstream the vectored WP once I write some tests. >>=20 >> I am not sure what the best way to detect that a page is write-pinned >> reliably. My point was that if a change is already carried to >> write-protect mechanisms, then this issue should be considered. = Because >> otherwise, many use-cases of uffd-wp would encounter implementation >> issues. >>=20 >> I will not =E2=80=9Ckill=E2=80=9D myself over it now, but I think it = worth consideration. >=20 > The current interface change is small and limited only to the extra = -ENOMEM > retval with memory pressures (personally I don't really know how to = trigger > this, as I never succeeded myself even with memory pressure..). What = you > said does sound like a new area to explore, and I think it's fine to = change > the interface again. Understood. Thanks and sorry again for the late response, Nadav=