From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 42152CD6E55 for ; Mon, 1 Jun 2026 16:08:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 54B706B044B; Mon, 1 Jun 2026 12:08:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4FC6D6B044D; Mon, 1 Jun 2026 12:08:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3EB0B6B044E; Mon, 1 Jun 2026 12:08:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 2D0A46B044B for ; Mon, 1 Jun 2026 12:08:02 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id E306BC2466 for ; Mon, 1 Jun 2026 16:08:01 +0000 (UTC) X-FDA: 84831825162.01.0042E85 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) by imf27.hostedemail.com (Postfix) with ESMTP id 08A3F40010 for ; Mon, 1 Jun 2026 16:07:59 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KFCrv1SH; spf=pass (imf27.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.188 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780330080; b=LCs7d/dnPkfI3M1JEwP/oQ39n5ZRKtVAE837LHR5cmUfMzZqGl4bOHkbP/8bOyDFZFNkQ1 n0LGTgx8jmELB8pb1STPLnf303xVTQyGjUQvsTyTjL5COV0D93vIuMF7TbqiivPujOwXHS jwq7aUrN973gzwJ+ohO+sr41wt2wA/I= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KFCrv1SH; spf=pass (imf27.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.188 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780330080; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=hE1QzaSPeeuEtKpkpB1CtsBNbDEAW/Bexb+NhfT6llo=; b=K6qWk06oSmXxtVq0/m39DVhRUmcsw7hAa7RnugU9Mv+rJkaj+x7g5KcOvTWNREmiDXK37l RlptCAnOlAZ/VB9vzdjqFbEFKdD2BYoSkTKFToB1FBu0KxHZSljGAZEz54qp7orWGxVhnA OMde6LUcly2YdYmHFR6sODzU+1VReRA= Message-ID: <76ff7922-bf54-472c-a628-ee191aeaf149@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780330077; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hE1QzaSPeeuEtKpkpB1CtsBNbDEAW/Bexb+NhfT6llo=; b=KFCrv1SHIW6rKf6zXja1OJy3cyn2UvdGKCE3ASX3JWUedBw+K0MFreVvLWyzIJ7q05O895 rvnhDuiR+5P9eKG7V9B0yQvbhmbdS8hrfybIXAU8pDudK2wZzqls5tbU4qer7NuOTc/QAp Jg8Y8lhEBuDUt90t+eGNkP5jGSXBzPs= Date: Tue, 2 Jun 2026 00:07:24 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse Content-Language: en-US To: "David Hildenbrand (Arm)" , Nico Pache Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com, usama.arif@linux.dev References: <2024af56-5e99-4799-a586-e9ba756cecb9@kernel.org> <20260601032804.96122-1-lance.yang@linux.dev> <616de1a8-1cfd-40b8-b04f-7b324be40bfd@linux.dev> <6b11bf0a-769c-4ef2-ac6f-2af38200a6bc@kernel.org> <06d9b665-945f-4967-9ed9-b06514478996@kernel.org> <0bb49c47-8c41-478c-847e-b9154c75e59c@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <0bb49c47-8c41-478c-847e-b9154c75e59c@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 08A3F40010 X-Rspam-User: X-Stat-Signature: zktxwuc1x3kg5rq7ke8w7uw8mqozdqyb X-HE-Tag: 1780330079-839237 X-HE-Meta: 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 O6+Zp3Ga tVBLlO7joZMXYIdX1bjitSXAHrwxGSZfOiqMDI5ilOIJXj96cMFXj0+ojJ3scwazC1MuE6cMp+/i7QhvtD2sZCbvLCxNlCp7rX4xyUbaGnAwbVAIXC7cqShA+0v8OEPpPQg1lICYx0b3RqfquafBqm6bbC2xz6I0Q82vsibj2VKmtMq7pPMtTcawdeBvVu9vgP0BagaHwbMhP/B/21RbIzFd/ESdsySpGm9kuzeAEje6Mv04FSTHOyLnkL7+C5lR/36ivgfjoZzoTyV3/RDxmEjwEsyqAJTOvY/rtIrpSVOM+hksmBgkksPBT5vMdVyE4ws1DSkdJpDSulE30OZduWBrtZqxmtiEaqA4SgUlWG5p1D2r1uuOWhcfBUBrz+d7nC1nW Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/6/1 23:05, David Hildenbrand (Arm) wrote: > On 6/1/26 17:00, Nico Pache wrote: >> On Mon, Jun 1, 2026 at 5:14 AM David Hildenbrand (Arm) wrote: >>> >>> On 6/1/26 12:47, Lance Yang wrote: >>>> >>>> >>>> >>>> Ah, cool! __folio_mark_uptodate() already does the job :P >>>> >>>> So yeah, no extra smp_wmb() needed here! >>> >>> Yeah. BTW, I think we'd need a spin_lock_nested(), so @Nico, treat my code as a >>> draft. >> >> Okay, I read the above and did some investigating. >> >> I will try to implement and verify the changes you suggested :) >> >> Or an even crazier idea... what if we ensure MIPS checks for PMD_none >> before walking a PTE table? > > But how would they update the cache then correctly? > > I'm too non-MIPS to know the answer :) Right, that's my concern as well ... If MIPS sees pmd_none(), it has no PTE table to walk, so it also has no way to do the cache update it wanted to do, I guess :) But, the PTE table is not really gone there. khugepaged only cleared the PMD temporarily while still using the old PTE table through _pmd. So I'd go with David's suggestion: " Best to make sure the page table is already installed when updating the entries. " Cheers, Lance