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AJvYcCVyPka5Z9rukGZe9+xC2/HLWbuewfAtOUMCV90BYCTUkkjjJ+HkDbvGmtrzT09KZG+JtFPJNjkDEw==@kvack.org X-Gm-Message-State: AOJu0YxfH+2kkafcqw6gTlBbVSnoofRMUfyx8WMjcnaRnAJ9xd7LUHyB 6bdBq9XqcGjtIxn1s5aW3fXmHRcFEFSB57Uxe+Wo11e77MnjByLpPwgsQ681yJrr2Hl+tptZM+S fBcPhJIsJr3GBlA1rfppmuxR1gQ== X-Google-Smtp-Source: AGHT+IH4/xFas5qH9WkGtquuXdWcMilu78LEjzqF2BsDWfyKCYslt2SGwsXQ1h75MU0H2eQyEYDJZApNSPXmxa7tZQ== X-Received: from pjff12.prod.google.com ([2002:a17:90b:562c:b0:32e:ddac:6ea5]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ef0f:b0:24c:965a:f97e with SMTP id d9443c01a7336-26811ba541dmr70869245ad.2.1758178422688; Wed, 17 Sep 2025 23:53:42 -0700 (PDT) Date: Thu, 18 Sep 2025 06:53:41 +0000 In-Reply-To: <20250916222801.dlew6mq7kog2q5ni@amd.com> Mime-Version: 1.0 References: <2ae41e0d80339da2b57011622ac2288fed65cd01.1747264138.git.ackerleytng@google.com> <20250916222801.dlew6mq7kog2q5ni@amd.com> Message-ID: Subject: Re: [RFC PATCH v2 35/51] mm: guestmem_hugetlb: Add support for splitting and merging pages From: Ackerley Tng To: Michael Roth Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, aik@amd.com, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, david@redhat.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, thomas.lendacky@amd.com, usama.arif@bytedance.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: F0299C0002 X-Stat-Signature: 3o6jnkjt615k35zr4pkogsixwzowajo3 X-HE-Tag: 1758178423-870223 X-HE-Meta: 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 KCNM7ZV3 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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: List-Subscribe: List-Unsubscribe: Michael Roth writes: > On Wed, May 14, 2025 at 04:42:14PM -0700, Ackerley Tng wrote: >> >> [...snip...] >> > > Hi Ackerley, > > We've been doing some testing with this series on top of David's > guestmemfd-preview branch with some SNP enablement[1][2] to exercise > this code along with the NUMA support from Shivank (BTW, I know you > have v3 in the works so let me know if we can help with testing that > as well). > Thank you for offering! I'm quite backed up now with some internal work. Will definitely appreciate all the help I can get once I manage to push out an RFCv3! > One issue we hit is if you do a split->merge sequence the unstash of the > private data will result in folio_test_hugetlb_vmemmap_optimized() reporting > true even though the hugetlb_vmemmap_optimize_folio() call hasn't been > performed yet, and when that does get called it will be skipped, so some HVO > optimization can be lost in this way. > > More troublesome however is if you later split the folio again, > hugetlb_vmemmap_restore_folio() may cause a BUG_ON() since the flags are in a > state that's not consistent with the state of the folio/vmemmap. > > The following patch seems to resolve the issue but I'm not sure what the > best approach would be: > > https://github.com/AMDESE/linux/commit/b1f25956f18d32730b8d4ded6d77e980091eb4d3 > I saw your reply on the other thread. Thanks for informing me :) > Thanks, > > Mike > > [1] https://github.com/AMDESE/linux/commits/snp-hugetlb-v2-wip0/ > [2] https://github.com/AMDESE/qemu/tree/snp-hugetlb-dev-wip0