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[2003:cb:c704:1100:65a0:c03a:142a:f914]) by smtp.gmail.com with ESMTPSA id q12-20020adff50c000000b002bc83b85180sm7289389wro.114.2023.01.23.03.09.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jan 2023 03:09:23 -0800 (PST) Message-ID: <84effdd8-1b67-4451-0fc4-a9e39210e5f1@redhat.com> Date: Mon, 23 Jan 2023 12:09:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH] mm/khugepaged: fix collapse_pte_mapped_thp() to allow anon_vma To: Zach O'Keefe Cc: Yang Shi , Hugh Dickins , Andrew Morton , Jann Horn , Song Liu , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <32be06f-f64-6632-4c36-bed7c0695a3b@google.com> <7ff97950-b524-db06-9ad6-e98b80dcfefa@redhat.com> <86d5f618-800d-9672-56c4-9309ef222a39@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F037A8001D X-Stat-Signature: u6k1zt7aprjhwtnbtbzn98nrtudnzapi X-Rspam-User: X-HE-Tag: 1674472168-952437 X-HE-Meta: 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 wIbuXeJy 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 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 18.01.23 00:00, Zach O'Keefe wrote: > On Mon, Jan 9, 2023 at 12:50 AM David Hildenbrand wrote: >> >>>>>>>> >>>>>>>> Side note: set_huge_pmd() wins the award of "ugliest mm function of early >>>>>>>> 2023". I was briefly concerned how do_set_pmd() decides whether the PMD can be >>>>>>>> writable or not. Turns out it's communicated via vm_fault->flags. Just >>>>>>>> horrible. >>> > > Hey David, > > Sorry for the late response here. > >>> My first Linux award! :) At least it's not "worst mm security issue of >>> early 2023". I'll take it! >> >> Good that you're not taking my words the wrong way. >> >> MADV_COLLAPSE is a very useful feature (especially also for THP tests >> [1]). I wish I could have looked at some of the patches earlier. But we >> cannot wait forever to get something merged, otherwise we'd never get >> bigger changes upstream. >> >> ... so there is plenty of time left in 2023 to cleanup khugepaged.c :P >> >> >> [1] https://lkml.kernel.org/r/20230104144905.460075-1-david@redhat.com > > Yes, thank you for these tests. I have them open in another tab along > with a mental TODO to take a closer look at them, and response > half-written. In-place collapse of anonymous memory *is* something > that I was interested in exploring later (I have a use-case for it; > hugepage-aware malloc() implementations). I'm taking so long on it > (sorry) b/c I need to review your point (2) (all PTE's mapping > exclusively). Hopefully I can get to it shortly. Cool, please let me know if you have any questions. Being able to in-place collapse a PTE-mapped anon THP again would be nice. -- Thanks, David / dhildenb