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[54.240.197.234]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48fed553116sm6323846f8f.42.2026.11.04.16.01.27 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 04 Nov 2026 16:01:28 -0800 (PST) From: Fred Griffoul To: Sean Christopherson , Paolo Bonzini Cc: Mushahid Hussain , nh-open-source@amazon.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 0/2] KVM: Allocate small memslot metadata with kvzalloc() Date: Thu, 5 Nov 2026 00:01:25 +0000 Message-ID: <20261105000127.63664-1-griffoul@gmail.com> X-Mailer: git-send-email 2.47.3 X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Fred Griffoul __vcalloc() makes every memslot metadata allocation at least one page, so small memslots waste most of their lpage_info and dirty bitmap, and memslots below 512 GiB waste most of a page on their 1 GiB lpage_info. Mushahid's patch [1] switched those arrays to kvcalloc(), and Sean suggested dedicated helpers for memslot metadata with a pivot that makes sense for KVM instead [2]. Patch 1 adds the helpers and routes the dirty bitmap, rmaps, lpage_info and write-tracking arrays through them, with no functional change. Patch 2 makes the helpers use kvzalloc() up to KMALLOC_MAX_CACHE_SIZE, where kmalloc() never uses more memory than vmalloc(), and keeps __vcalloc() above. I ran the memslot and dirty logging selftests with the TDP MMU and with kvm.tdp_mmu=0, plus a check that one-page memslots no longer take a vmalloc area each and that a 1 TiB memslot still gets its rmaps from vmalloc. Fred Changes in v2: - Split the helpers and the allocator change into two patches - Pivot on KMALLOC_MAX_CACHE_SIZE instead of INT_MAX v1: https://lore.kernel.org/kvm/20261103234734.45413-1-griffoul@gmail.com/ [1] https://lore.kernel.org/all/20260815142218.85067-1-hmushi@amazon.co.uk/ [2] https://lore.kernel.org/all/arr1VgGZmgUmY4hc@google.com/ Fred Griffoul (2): KVM: Add helpers to allocate memslot metadata KVM: Use kvzalloc() for memslot metadata that fits in a slab bucket arch/x86/kvm/mmu/page_track.c | 6 +++--- arch/x86/kvm/x86.c | 10 +++++----- include/linux/kvm_host.h | 2 ++ virt/kvm/kvm_main.c | 22 ++++++++++++++++++++-- 4 files changed, 30 insertions(+), 10 deletions(-) base-commit: d21eef2084a9af87ac2a783bc7c2b175ba114e4e -- 2.47.3