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AJvYcCXaFNZwDOOiYnv1GJkbdHp66WGxo3X38stJNDSPR003ffYS+7PkyPzlzDqJ7NbmHVUH5NClcRe7nXykvMMq@vger.kernel.org X-Gm-Message-State: AOJu0YxwyldRAhXkGbvSlSRmSDRWmTfM9myfLKp8nWFOaNTO+2eiWwop L6Z1oosq5TR066N1qoGBIcCamv5aXbePMt11qCTxLDOg+9ZEjAZDbc3D1XGQxi/cVQws4N/8KLl UH1nSDLp6CgKeIe08NYloIRcRow== X-Google-Smtp-Source: AGHT+IH8htB84vea5MhC0iZOF6Zxpq5a9Lmv6Or6O2Uq8VlBTS29CnJcDsUC/JtlL3nBkV61UZOUO9/cw62YUQKDXQ== X-Received: from pfiy14.prod.google.com ([2002:a05:6a00:190e:b0:746:2747:e782]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:cc6:b0:742:a23e:2a68 with SMTP id d2e1a72fcca58-7482806455cmr981739b3a.15.1749151020845; Thu, 05 Jun 2025 12:17:00 -0700 (PDT) Date: Thu, 05 Jun 2025 12:16:59 -0700 In-Reply-To: <558a649d-d419-46e2-adb8-4027e105c1ce@linux.intel.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <7753dc66229663fecea2498cf442a768cb7191ba.1747264138.git.ackerleytng@google.com> <558a649d-d419-46e2-adb8-4027e105c1ce@linux.intel.com> Message-ID: Subject: Re: [RFC PATCH v2 38/51] KVM: guest_memfd: Split allocator pages for guest_memfd use From: Ackerley Tng To: Binbin Wu 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, 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, michael.roth@amd.com, 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" Binbin Wu writes: > On 5/15/2025 7:42 AM, Ackerley Tng wrote: > [...] >> + >> +static inline int kvm_gmem_try_split_folio_in_filemap(struct inode *inode, >> + struct folio *folio) >> +{ >> + size_t to_nr_pages; >> + void *priv; >> + >> + if (!kvm_gmem_has_custom_allocator(inode)) >> + return 0; >> + >> + priv = kvm_gmem_allocator_private(inode); >> + to_nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_page(priv); >> + >> + if (kvm_gmem_has_some_shared(inode, folio->index, to_nr_pages)) > > What if a huge page whose attribute is shared? > This checks if there are any shared pages in the range [folio->index, folio->index + to_nr_pages), so if the entire huge page is shared this function should also return true. folio->index is the start of the merged huge page, and to_nr_pages is the number of pages in the merged huge page, so this should be querying exactly the entire huge page. Note to self: rename kvm_gmem_has_some_shared() to kvm_gmem_has_any_shared() in the next revision. Hope I answered your question! Let me know if I misunderstood your question. >> + return kvm_gmem_split_folio_in_filemap(inode, folio); >> + >> + return 0; >> +} >> + > [...] >> >> static int kvm_gmem_shareability_setup(struct maple_tree *mt, loff_t size, u64 flags) >> @@ -563,11 +1005,16 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) >> return folio; >> >> if (kvm_gmem_has_custom_allocator(inode)) { >> - void *p = kvm_gmem_allocator_private(inode); >> + size_t nr_pages; >> + void *p; >> >> + p = kvm_gmem_allocator_private(inode); >> folio = kvm_gmem_allocator_ops(inode)->alloc_folio(p); >> if (IS_ERR(folio)) >> return folio; >> + >> + nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(p); >> + index_floor = round_down(index, nr_pages); >> } else { >> gfp_t gfp = mapping_gfp_mask(inode->i_mapping); >> >> @@ -580,10 +1027,11 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) >> folio_put(folio); >> return ERR_PTR(ret); >> } >> + >> + index_floor = index; >> } >> allocated_size = folio_size(folio); >> >> - index_floor = round_down(index, folio_nr_pages(folio)); >> ret = kvm_gmem_filemap_add_folio(inode->i_mapping, folio, index_floor); >> if (ret) { >> folio_put(folio); >> @@ -600,6 +1048,13 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) >> return ERR_PTR(ret); >> } >> >> + /* Leave just filemap's refcounts on folio. */ >> + folio_put(folio); >> + >> + ret = kvm_gmem_try_split_folio_in_filemap(inode, folio); > > When !CONFIG_KVM_GMEM_SHARED_MEM, kvm_gmem_try_split_folio_in_filemap() is > undefined. > Will fix this in the next revision. Thanks! >> + if (ret) >> + goto err; >> + >> spin_lock(&inode->i_lock); >> inode->i_blocks += allocated_size / 512; >> spin_unlock(&inode->i_lock); >> > [...]