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AJvYcCUOCh3iVrjpFMrvsgNSpLjk6dp0n1Rnminf7P+1u2/iez5NbZ+wPYkEZOLFl7/QPyIhCEjeOoJR68ZcvDE=@vger.kernel.org X-Gm-Message-State: AOJu0YwvmBRsrM+wuefIbpCChg/gEbegg3L9qNrSH2kLZKUsLzfkv3h5 il44XAuyhagySamfwNu9woH3YWnY4wpo4RcHTARFg0Lr8mOP7qML4jiSn52nhmtrV+x+zvy72j6 gQ3v50pvlFy808NPs3UGFag== X-Google-Smtp-Source: AGHT+IF9uxV4jKBR2ISNh3Rht7TIwj9ihxeO9BED9Bzl3yQgQuek7HskgQIB9opFNDkTcfi2+w8NurKVBa9O265TBw== X-Received: from pfbcb11.prod.google.com ([2002:a05:6a00:430b:b0:730:7e2d:df69]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3d09:b0:740:6f86:a0e6 with SMTP id d2e1a72fcca58-742984dafa0mr801571b3a.6.1747266184935; Wed, 14 May 2025 16:43:04 -0700 (PDT) Date: Wed, 14 May 2025 16:41:44 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.49.0.1045.g170613ef41-goog Message-ID: <37f60bbd7d408cf6d421d0582462488262c720ab.1747264138.git.ackerleytng@google.com> Subject: [RFC PATCH v2 05/51] KVM: guest_memfd: Skip LRU for guest_memfd folios From: Ackerley Tng To: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org Cc: ackerleytng@google.com, 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, 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" filemap_add_folio(), called from filemap_grab_folio(), adds the folio onto some LRU list, which is not necessary for guest_memfd since guest_memfd folios don't participate in any swapping. This patch reimplements part of filemap_add_folio() to avoid adding allocated guest_memfd folios to the filemap. With shared to private conversions dependent on refcounts, avoiding usage of LRU ensures that LRU lists no longer take any refcounts on guest_memfd folios and significantly reduces the chance of elevated refcounts during conversion. Signed-off-by: Ackerley Tng Change-Id: Ia2540d9fc132d46219e6e714fd42bc82a62a27fa --- mm/filemap.c | 1 + mm/memcontrol.c | 2 + virt/kvm/guest_memfd.c | 91 ++++++++++++++++++++++++++++++++++++++---- 3 files changed, 86 insertions(+), 8 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 7b90cbeb4a1a..bed7160db214 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -954,6 +954,7 @@ noinline int __filemap_add_folio(struct address_space *mapping, return xas_error(&xas); } ALLOW_ERROR_INJECTION(__filemap_add_folio, ERRNO); +EXPORT_SYMBOL_GPL(__filemap_add_folio); int filemap_add_folio(struct address_space *mapping, struct folio *folio, pgoff_t index, gfp_t gfp) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c96c1f2b9cf5..1def80570738 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4611,6 +4611,7 @@ int __mem_cgroup_charge(struct folio *folio, struct mm_struct *mm, gfp_t gfp) return ret; } +EXPORT_SYMBOL_GPL(__mem_cgroup_charge); /** * mem_cgroup_charge_hugetlb - charge the memcg for a hugetlb folio @@ -4785,6 +4786,7 @@ void __mem_cgroup_uncharge(struct folio *folio) uncharge_folio(folio, &ug); uncharge_batch(&ug); } +EXPORT_SYMBOL_GPL(__mem_cgroup_uncharge); void __mem_cgroup_uncharge_folios(struct folio_batch *folios) { diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index f802116290ce..6f6c4d298f8f 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -466,6 +466,38 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, return r; } +static int __kvm_gmem_filemap_add_folio(struct address_space *mapping, + struct folio *folio, pgoff_t index) +{ + void *shadow = NULL; + gfp_t gfp; + int ret; + + gfp = mapping_gfp_mask(mapping); + + __folio_set_locked(folio); + ret = __filemap_add_folio(mapping, folio, index, gfp, &shadow); + __folio_clear_locked(folio); + + return ret; +} + +/* + * Adds a folio to the filemap for guest_memfd. Skips adding the folio to any + * LRU list. + */ +static int kvm_gmem_filemap_add_folio(struct address_space *mapping, + struct folio *folio, pgoff_t index) +{ + int ret; + + ret = __kvm_gmem_filemap_add_folio(mapping, folio, index); + if (!ret) + folio_set_unevictable(folio); + + return ret; +} + /* * Returns a locked folio on success. The caller is responsible for * setting the up-to-date flag before the memory is mapped into the guest. @@ -477,8 +509,46 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, */ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) { + struct folio *folio; + gfp_t gfp; + int ret; + +repeat: + folio = filemap_lock_folio(inode->i_mapping, index); + if (!IS_ERR(folio)) + return folio; + + gfp = mapping_gfp_mask(inode->i_mapping); + /* TODO: Support huge pages. */ - return filemap_grab_folio(inode->i_mapping, index); + folio = filemap_alloc_folio(gfp, 0); + if (!folio) + return ERR_PTR(-ENOMEM); + + ret = mem_cgroup_charge(folio, NULL, gfp); + if (ret) { + folio_put(folio); + return ERR_PTR(ret); + } + + ret = kvm_gmem_filemap_add_folio(inode->i_mapping, folio, index); + if (ret) { + folio_put(folio); + + /* + * There was a race, two threads tried to get a folio indexing + * to the same location in the filemap. The losing thread should + * free the allocated folio, then lock the folio added to the + * filemap by the winning thread. + */ + if (ret == -EEXIST) + goto repeat; + + return ERR_PTR(ret); + } + + __folio_set_locked(folio); + return folio; } static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start, @@ -956,23 +1026,28 @@ static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *fol } #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE +static void kvm_gmem_invalidate(struct folio *folio) +{ + kvm_pfn_t pfn = folio_pfn(folio); + + kvm_arch_gmem_invalidate(pfn, pfn + folio_nr_pages(folio)); +} +#else +static inline void kvm_gmem_invalidate(struct folio *folio) {} +#endif + static void kvm_gmem_free_folio(struct folio *folio) { - struct page *page = folio_page(folio, 0); - kvm_pfn_t pfn = page_to_pfn(page); - int order = folio_order(folio); + folio_clear_unevictable(folio); - kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order)); + kvm_gmem_invalidate(folio); } -#endif static const struct address_space_operations kvm_gmem_aops = { .dirty_folio = noop_dirty_folio, .migrate_folio = kvm_gmem_migrate_folio, .error_remove_folio = kvm_gmem_error_folio, -#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE .free_folio = kvm_gmem_free_folio, -#endif }; static int kvm_gmem_getattr(struct mnt_idmap *idmap, const struct path *path, -- 2.49.0.1045.g170613ef41-goog