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Sun, 19 Apr 2026 14:58:36 -0400 X-MC-Unique: HXVqmU7gNNK66kPtndohEw-1 X-Mimecast-MFC-AGG-ID: HXVqmU7gNNK66kPtndohEw_1776625115 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1EB41195608D; Sun, 19 Apr 2026 18:58:35 +0000 (UTC) Received: from p1.redhat.com (unknown [10.22.74.5]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B7F571956095; Sun, 19 Apr 2026 18:58:13 +0000 (UTC) From: Nico Pache To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: 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, david@kernel.org, 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, lance.yang@linux.dev, Liam.Howlett@oracle.com, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, npache@redhat.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 Subject: [PATCH 7.2 v16 00/13] khugepaged: mTHP support Date: Sun, 19 Apr 2026 12:57:37 -0600 Message-ID: <20260419185750.260784-1-npache@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-MFC-PROC-ID: 5H1jjVMuEhWQHv5Mw7Y4xnm8NavPZtMYTAvq2Xm5Tok_1776625115 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true The following series provides khugepaged with the capability to collapse anonymous memory regions to mTHPs. To achieve this we generalize the khugepaged functions to no longer depend on PMD_ORDER. Then during the PMD scan, we use a bitmap to track individual pages that are occupied (!none/zero). After the PMD scan is done, we use the bitmap to find the optimal mTHP sizes for the PMD range. The restriction on max_ptes_none is removed during the scan, to make sure we account for the whole PMD range in the bitmap. When no mTHP size is enabled, the legacy behavior of khugepaged is maintained. We currently only support max_ptes_none values of 0 or HPAGE_PMD_NR - 1 (ie 511). If any other value is specified, the kernel will emit a warning and no mTHP collapse will be attempted. If a mTHP collapse is attempted, but contains swapped out, or shared pages, we don't perform the collapse. It is now also possible to collapse to mTHPs without requiring the PMD THP size to be enabled. These limitations are to prevent collapse "creep" behavior. This prevents constantly promoting mTHPs to the next available size, which would occur because a collapse introduces more non-zero pages that would satisfy the promotion condition on subsequent scans. Patch 1-2: Generalize hugepage_vma_revalidate and alloc_charge_folio for arbitrary orders. Patch 3: Rework max_ptes_* handling into helper functions Patch 4-5: Generalize __collapse_huge_page_* and collapse_huge_page Patch 6: Skip collapsing mTHP to smaller orders Patch 7-8: Add per-order mTHP statistics and tracepoints Patch 9: Introduce collapse_allowable_orders helper function Patch 10-12: Introduce bitmap and mTHP collapse support, fully enabled Patch 13: Documentation Testing: - Built for x86_64, aarch64, ppc64le, and s390x - ran all arches on test suites provided by the kernel-tests project - internal testing suites: functional testing and performance testing - selftests mm - I created a test script that I used to push khugepaged to its limits while monitoring a number of stats and tracepoints. The code is available here[1] (Run in legacy mode for these changes and set mthp sizes to inherit) The summary from my testings was that there was no significant regression noticed through this test. In some cases my changes had better collapse latencies, and was able to scan more pages in the same amount of time/work, but for the most part the results were consistent. - redis testing. I did some testing with these changes along with my defer changes (see followup [2] post for more details). We've decided to get the mTHP changes merged first before attempting the defer series. - some basic testing on 64k page size. - lots of general use. V16 Changes: - This was quite the respin, so hopefully everything is ok! I dropped some acks/rb on patches that changed significantly. Major changes are related to the locking cleanup in collapse_huge_page(). sorry if i missed any feedback there was quite a bit of minor requests - New cleanup patch: introduce collapse_max_ptes_none/shared/swap() helpers, absorbing madvise_collapse special-casing (David) - Merge "introduce collapse_max_ptes_none helper" into the generalize __collapse_huge_page_* patch, dropping the separate patch (David) - Simplify collapse_huge_page() locking: move mmap_read_unlock() to caller, remove mmap_locked tracking parameter entirely (Lorenzo) - Use enum tva_type instead of bool is_khugepaged in collapse_allowable_orders() (David, Lorenzo) - collapse_allowable_orders() takes (vma, tva_flags), accesses vma->vm_flags internally (Lorenzo) - Rename mthp_* functions to collapse_mthp_* prefix (David, Lorenzo) - Use MAX_PTRS_PER_PTE consistently for bitmap ops (Lorenzo) - Downgrade BUG_ON() to WARN_ON_ONCE() in collapse_huge_page() (Lorenzo) - Add /*expect_anon=*/true annotation to revalidate calls (Lorenzo) - Pull common spin_lock + WARN_ON_ONCE out of PMD/mTHP branch (Lorenzo) - Fix pteval declaration style; use end_addr variable (Lorenzo) - Use ternary for result assignment in collapse_scan_pmd() (Lorenzo) - Improve anon_vma locking comment for mTHP case (Lorenzo) - Document why skip-smaller-order isn't done in scan phase (David) - Make documentation of max_ptes_none mTHP behavior (only 0 and HPAGE_PMD_NR-1 supported) in admin guide more apparent. (David, Lorenzo) - Collect new Acks/RB tags from v15 review V15: https://lore.kernel.org/all/20260226031741.230674-1-npache@redhat.com V14: https://lore.kernel.org/all/20260122192841.128719-1-npache@redhat.com V13: https://lore.kernel.org/all/20251201174627.23295-1-npache@redhat.com V12: https://lore.kernel.org/all/20251022183717.70829-1-npache@redhat.com V11: https://lore.kernel.org/all/20250912032810.197475-1-npache@redhat.com V10: https://lore.kernel.org/all/20250819134205.622806-1-npache@redhat.com V9 : https://lore.kernel.org/all/20250714003207.113275-1-npache@redhat.com V8 : https://lore.kernel.org/all/20250702055742.102808-1-npache@redhat.com V7 : https://lore.kernel.org/all/20250515032226.128900-1-npache@redhat.com V6 : https://lore.kernel.org/all/20250515030312.125567-1-npache@redhat.com V5 : https://lore.kernel.org/all/20250428181218.85925-1-npache@redhat.com V4 : https://lore.kernel.org/all/20250417000238.74567-1-npache@redhat.com V3 : https://lore.kernel.org/all/20250414220557.35388-1-npache@redhat.com V2 : https://lore.kernel.org/all/20250211003028.213461-1-npache@redhat.com V1 : https://lore.kernel.org/all/20250108233128.14484-1-npache@redhat.com A big thanks to everyone that has reviewed, tested, and participated in the development process. Its been a great experience working with all of you on this endeavor. [1] - https://gitlab.com/npache/khugepaged_mthp_test [2] - https://lore.kernel.org/lkml/20250515033857.132535-1-npache@redhat.com/ Baolin Wang (1): mm/khugepaged: run khugepaged for all orders Dev Jain (1): mm/khugepaged: generalize alloc_charge_folio() Nico Pache (11): mm/khugepaged: generalize hugepage_vma_revalidate for mTHP support mm/khugepaged: rework max_ptes_* handling with helper functions mm/khugepaged: generalize __collapse_huge_page_* for mTHP support mm/khugepaged: generalize collapse_huge_page for mTHP collapse mm/khugepaged: skip collapsing mTHP to smaller orders mm/khugepaged: add per-order mTHP collapse failure statistics mm/khugepaged: improve tracepoints for mTHP orders mm/khugepaged: introduce collapse_allowable_orders helper function mm/khugepaged: Introduce mTHP collapse support mm/khugepaged: avoid unnecessary mTHP collapse attempts Documentation: mm: update the admin guide for mTHP collapse Documentation/admin-guide/mm/transhuge.rst | 81 ++- include/linux/huge_mm.h | 5 + include/linux/khugepaged.h | 6 +- include/trace/events/huge_memory.h | 34 +- mm/huge_memory.c | 13 +- mm/khugepaged.c | 623 ++++++++++++++++----- mm/vma.c | 6 +- tools/testing/vma/include/stubs.h | 3 +- 8 files changed, 589 insertions(+), 182 deletions(-) base-commit: 4569c01e84d440f1f6c79df1e13e9c86a9fb80ca -- 2.53.0