Documentation/admin-guide/mm/transhuge.rst | 80 ++- include/linux/huge_mm.h | 5 + include/trace/events/huge_memory.h | 34 +- mm/huge_memory.c | 11 + mm/khugepaged.c | 696 +++++++++++++++------ mm/mremap.c | 2 +- 6 files changed, 618 insertions(+), 210 deletions(-)
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 limitiations 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: Refactor/rename hpage_collapse Patch 2: Refactoring to combine madvise_collapse and khugepaged Patch 3-8: Generalize khugepaged functions for arbitrary orders and introduce some helper functions Patch 9: skip collapsing mTHP to smaller orders Patch 10-11: Add per-order mTHP statistics and tracepoints Patch 12: Introduce collapse_allowable_orders Patch 13-15: Introduce bitmap and mTHP collapse support, fully enabled Patch 16: Documentation --------- Testing --------- - Built for x86_64, aarch64, ppc64le, and s390x - 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 tested 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. V13 Changes: - Lots of minor nits, cleanups, comments, and renames - Bitmap function simplification and more helpers (Wei, Lorenzo) - Max_ptes_none (0 or 511) restriction - commit description expansion - list all reachable enum values in mthp_collapse() - Fix ppc64 compile error due to using HPAGE_PMD_ORDER (replace with ilog2(MAX_PTRS_PER_PTE)) V12: https://lore.kernel.org/lkml/20251022183717.70829-1-npache@redhat.com/ V11: https://lore.kernel.org/lkml/20250912032810.197475-1-npache@redhat.com/ V10: https://lore.kernel.org/lkml/20250819134205.622806-1-npache@redhat.com/ V9 : https://lore.kernel.org/lkml/20250714003207.113275-1-npache@redhat.com/ V8 : https://lore.kernel.org/lkml/20250702055742.102808-1-npache@redhat.com/ V7 : https://lore.kernel.org/lkml/20250515032226.128900-1-npache@redhat.com/ V6 : https://lore.kernel.org/lkml/20250515030312.125567-1-npache@redhat.com/ V5 : https://lore.kernel.org/lkml/20250428181218.85925-1-npache@redhat.com/ V4 : https://lore.kernel.org/lkml/20250417000238.74567-1-npache@redhat.com/ V3 : https://lore.kernel.org/lkml/20250414220557.35388-1-npache@redhat.com/ V2 : https://lore.kernel.org/lkml/20250211003028.213461-1-npache@redhat.com/ V1 : https://lore.kernel.org/lkml/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 endeavour. [1] - https://gitlab.com/npache/khugepaged_mthp_test [2] - https://lore.kernel.org/lkml/20250515033857.132535-1-npache@redhat.com/ Baolin Wang (1): khugepaged: run khugepaged for all orders Dev Jain (1): khugepaged: generalize alloc_charge_folio() Nico Pache (14): khugepaged: rename hpage_collapse_* to collapse_* introduce collapse_single_pmd to unify khugepaged and madvise_collapse khugepaged: generalize hugepage_vma_revalidate for mTHP support khugepaged: introduce is_mthp_order helper khugepaged: generalize __collapse_huge_page_* for mTHP support khugepaged: introduce collapse_max_ptes_none helper function khugepaged: generalize collapse_huge_page for mTHP collapse khugepaged: skip collapsing mTHP to smaller orders khugepaged: add per-order mTHP collapse failure statistics khugepaged: improve tracepoints for mTHP orders khugepaged: introduce collapse_allowable_orders helper function khugepaged: Introduce mTHP collapse support khugepaged: avoid unnecessary mTHP collapse attempts Documentation: mm: update the admin guide for mTHP collapse Documentation/admin-guide/mm/transhuge.rst | 80 ++- include/linux/huge_mm.h | 5 + include/trace/events/huge_memory.h | 34 +- mm/huge_memory.c | 11 + mm/khugepaged.c | 696 +++++++++++++++------ mm/mremap.c | 2 +- 6 files changed, 618 insertions(+), 210 deletions(-) -- 2.51.1
(Sorry for multiple mails replying to same, lei/lore are broken again so my setup isn't working properly). I tried to fixup the conflicts here to run tests locally but there's too many and I messed it up. Could you please resend this series rebased on mm-unstable please? Thanks, Lorenzo On Mon, Dec 01, 2025 at 10:46:11AM -0700, Nico Pache wrote: > 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 limitiations 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: Refactor/rename hpage_collapse > Patch 2: Refactoring to combine madvise_collapse and khugepaged > Patch 3-8: Generalize khugepaged functions for arbitrary orders and > introduce some helper functions > Patch 9: skip collapsing mTHP to smaller orders > Patch 10-11: Add per-order mTHP statistics and tracepoints > Patch 12: Introduce collapse_allowable_orders > Patch 13-15: Introduce bitmap and mTHP collapse support, fully enabled > Patch 16: Documentation > > --------- > Testing > --------- > - Built for x86_64, aarch64, ppc64le, and s390x > - 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 tested 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. > > V13 Changes: > - Lots of minor nits, cleanups, comments, and renames > - Bitmap function simplification and more helpers (Wei, Lorenzo) > - Max_ptes_none (0 or 511) restriction > - commit description expansion > - list all reachable enum values in mthp_collapse() > - Fix ppc64 compile error due to using HPAGE_PMD_ORDER (replace with > ilog2(MAX_PTRS_PER_PTE)) > > V12: https://lore.kernel.org/lkml/20251022183717.70829-1-npache@redhat.com/ > V11: https://lore.kernel.org/lkml/20250912032810.197475-1-npache@redhat.com/ > V10: https://lore.kernel.org/lkml/20250819134205.622806-1-npache@redhat.com/ > V9 : https://lore.kernel.org/lkml/20250714003207.113275-1-npache@redhat.com/ > V8 : https://lore.kernel.org/lkml/20250702055742.102808-1-npache@redhat.com/ > V7 : https://lore.kernel.org/lkml/20250515032226.128900-1-npache@redhat.com/ > V6 : https://lore.kernel.org/lkml/20250515030312.125567-1-npache@redhat.com/ > V5 : https://lore.kernel.org/lkml/20250428181218.85925-1-npache@redhat.com/ > V4 : https://lore.kernel.org/lkml/20250417000238.74567-1-npache@redhat.com/ > V3 : https://lore.kernel.org/lkml/20250414220557.35388-1-npache@redhat.com/ > V2 : https://lore.kernel.org/lkml/20250211003028.213461-1-npache@redhat.com/ > V1 : https://lore.kernel.org/lkml/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 endeavour. > > [1] - https://gitlab.com/npache/khugepaged_mthp_test > [2] - https://lore.kernel.org/lkml/20250515033857.132535-1-npache@redhat.com/ > > Baolin Wang (1): > khugepaged: run khugepaged for all orders > > Dev Jain (1): > khugepaged: generalize alloc_charge_folio() > > Nico Pache (14): > khugepaged: rename hpage_collapse_* to collapse_* > introduce collapse_single_pmd to unify khugepaged and madvise_collapse > khugepaged: generalize hugepage_vma_revalidate for mTHP support > khugepaged: introduce is_mthp_order helper > khugepaged: generalize __collapse_huge_page_* for mTHP support > khugepaged: introduce collapse_max_ptes_none helper function > khugepaged: generalize collapse_huge_page for mTHP collapse > khugepaged: skip collapsing mTHP to smaller orders > khugepaged: add per-order mTHP collapse failure statistics > khugepaged: improve tracepoints for mTHP orders > khugepaged: introduce collapse_allowable_orders helper function > khugepaged: Introduce mTHP collapse support > khugepaged: avoid unnecessary mTHP collapse attempts > Documentation: mm: update the admin guide for mTHP collapse > > Documentation/admin-guide/mm/transhuge.rst | 80 ++- > include/linux/huge_mm.h | 5 + > include/trace/events/huge_memory.h | 34 +- > mm/huge_memory.c | 11 + > mm/khugepaged.c | 696 +++++++++++++++------ > mm/mremap.c | 2 +- > 6 files changed, 618 insertions(+), 210 deletions(-) > > -- > 2.51.1 >
On Thu, Jan 8, 2026 at 10:20 AM Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote: > > (Sorry for multiple mails replying to same, lei/lore are broken again so my > setup isn't working properly). > > I tried to fixup the conflicts here to run tests locally but there's too many > and I messed it up. > > Could you please resend this series rebased on mm-unstable please? Yes ofc! fixed all the conflicts yesterday, just finalizing my testing. Should be out tomorrow or Thursday. > > Thanks, Lorenzo > > On Mon, Dec 01, 2025 at 10:46:11AM -0700, Nico Pache wrote: > > 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 limitiations 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: Refactor/rename hpage_collapse > > Patch 2: Refactoring to combine madvise_collapse and khugepaged > > Patch 3-8: Generalize khugepaged functions for arbitrary orders and > > introduce some helper functions > > Patch 9: skip collapsing mTHP to smaller orders > > Patch 10-11: Add per-order mTHP statistics and tracepoints > > Patch 12: Introduce collapse_allowable_orders > > Patch 13-15: Introduce bitmap and mTHP collapse support, fully enabled > > Patch 16: Documentation > > > > --------- > > Testing > > --------- > > - Built for x86_64, aarch64, ppc64le, and s390x > > - 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 tested 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. > > > > V13 Changes: > > - Lots of minor nits, cleanups, comments, and renames > > - Bitmap function simplification and more helpers (Wei, Lorenzo) > > - Max_ptes_none (0 or 511) restriction > > - commit description expansion > > - list all reachable enum values in mthp_collapse() > > - Fix ppc64 compile error due to using HPAGE_PMD_ORDER (replace with > > ilog2(MAX_PTRS_PER_PTE)) > > > > V12: https://lore.kernel.org/lkml/20251022183717.70829-1-npache@redhat.com/ > > V11: https://lore.kernel.org/lkml/20250912032810.197475-1-npache@redhat.com/ > > V10: https://lore.kernel.org/lkml/20250819134205.622806-1-npache@redhat.com/ > > V9 : https://lore.kernel.org/lkml/20250714003207.113275-1-npache@redhat.com/ > > V8 : https://lore.kernel.org/lkml/20250702055742.102808-1-npache@redhat.com/ > > V7 : https://lore.kernel.org/lkml/20250515032226.128900-1-npache@redhat.com/ > > V6 : https://lore.kernel.org/lkml/20250515030312.125567-1-npache@redhat.com/ > > V5 : https://lore.kernel.org/lkml/20250428181218.85925-1-npache@redhat.com/ > > V4 : https://lore.kernel.org/lkml/20250417000238.74567-1-npache@redhat.com/ > > V3 : https://lore.kernel.org/lkml/20250414220557.35388-1-npache@redhat.com/ > > V2 : https://lore.kernel.org/lkml/20250211003028.213461-1-npache@redhat.com/ > > V1 : https://lore.kernel.org/lkml/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 endeavour. > > > > [1] - https://gitlab.com/npache/khugepaged_mthp_test > > [2] - https://lore.kernel.org/lkml/20250515033857.132535-1-npache@redhat.com/ > > > > Baolin Wang (1): > > khugepaged: run khugepaged for all orders > > > > Dev Jain (1): > > khugepaged: generalize alloc_charge_folio() > > > > Nico Pache (14): > > khugepaged: rename hpage_collapse_* to collapse_* > > introduce collapse_single_pmd to unify khugepaged and madvise_collapse > > khugepaged: generalize hugepage_vma_revalidate for mTHP support > > khugepaged: introduce is_mthp_order helper > > khugepaged: generalize __collapse_huge_page_* for mTHP support > > khugepaged: introduce collapse_max_ptes_none helper function > > khugepaged: generalize collapse_huge_page for mTHP collapse > > khugepaged: skip collapsing mTHP to smaller orders > > khugepaged: add per-order mTHP collapse failure statistics > > khugepaged: improve tracepoints for mTHP orders > > khugepaged: introduce collapse_allowable_orders helper function > > khugepaged: Introduce mTHP collapse support > > khugepaged: avoid unnecessary mTHP collapse attempts > > Documentation: mm: update the admin guide for mTHP collapse > > > > Documentation/admin-guide/mm/transhuge.rst | 80 ++- > > include/linux/huge_mm.h | 5 + > > include/trace/events/huge_memory.h | 34 +- > > mm/huge_memory.c | 11 + > > mm/khugepaged.c | 696 +++++++++++++++------ > > mm/mremap.c | 2 +- > > 6 files changed, 618 insertions(+), 210 deletions(-) > > > > -- > > 2.51.1 > > >
On 1/8/26 18:19, Lorenzo Stoakes wrote: > (Sorry for multiple mails replying to same, lei/lore are broken again so my > setup isn't working properly). > > I tried to fixup the conflicts here to run tests locally but there's too many > and I messed it up. > > Could you please resend this series rebased on mm-unstable please? And maybe send out the two cleanups that can be applied earlier separately? -- Cheers David
On Fri, Jan 9, 2026 at 6:57 AM David Hildenbrand (Red Hat) <david@kernel.org> wrote: > > On 1/8/26 18:19, Lorenzo Stoakes wrote: > > (Sorry for multiple mails replying to same, lei/lore are broken again so my > > setup isn't working properly). > > > > I tried to fixup the conflicts here to run tests locally but there's too many > > and I messed it up. > > > > Could you please resend this series rebased on mm-unstable please? > > > And maybe send out the two cleanups that can be applied earlier separately? Yeah I can do that. I'll just add a `dependent line` when I post the v14. > > -- > Cheers > > David >
On Fri, Jan 09, 2026 at 02:57:16PM +0100, David Hildenbrand (Red Hat) wrote: > On 1/8/26 18:19, Lorenzo Stoakes wrote: > > (Sorry for multiple mails replying to same, lei/lore are broken again so my > > setup isn't working properly). > > > > I tried to fixup the conflicts here to run tests locally but there's too many > > and I messed it up. > > > > Could you please resend this series rebased on mm-unstable please? > > > And maybe send out the two cleanups that can be applied earlier separately? Yeah sounds sensible. > > -- > Cheers > > David Cheers, Lorenzo
One nit on this series - you sent it on the 1st day of the merge window :) We unfortunately have a suboptimal approach to the merge window in mm in my view. Unfortunately it seems unlikely to change any time soon, so I would simply politely ask that in future esp. with big series whether you could send a respin within a cycle? :) Sorry for the longer delay here btw, I've been on leave after that! Unfortunate timing. Note that I am scaling down my review somewhat at the moment as I am simply disinclined to deal with the merge-by-default insanity mm engages in any longer, but since I promised to review this I will do so. Cheers, Lorenzo On Mon, Dec 01, 2025 at 10:46:11AM -0700, Nico Pache wrote: > 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 limitiations 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: Refactor/rename hpage_collapse > Patch 2: Refactoring to combine madvise_collapse and khugepaged > Patch 3-8: Generalize khugepaged functions for arbitrary orders and > introduce some helper functions > Patch 9: skip collapsing mTHP to smaller orders > Patch 10-11: Add per-order mTHP statistics and tracepoints > Patch 12: Introduce collapse_allowable_orders > Patch 13-15: Introduce bitmap and mTHP collapse support, fully enabled > Patch 16: Documentation > > --------- > Testing > --------- > - Built for x86_64, aarch64, ppc64le, and s390x > - 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 tested 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. > > V13 Changes: > - Lots of minor nits, cleanups, comments, and renames > - Bitmap function simplification and more helpers (Wei, Lorenzo) > - Max_ptes_none (0 or 511) restriction > - commit description expansion > - list all reachable enum values in mthp_collapse() > - Fix ppc64 compile error due to using HPAGE_PMD_ORDER (replace with > ilog2(MAX_PTRS_PER_PTE)) > > V12: https://lore.kernel.org/lkml/20251022183717.70829-1-npache@redhat.com/ > V11: https://lore.kernel.org/lkml/20250912032810.197475-1-npache@redhat.com/ > V10: https://lore.kernel.org/lkml/20250819134205.622806-1-npache@redhat.com/ > V9 : https://lore.kernel.org/lkml/20250714003207.113275-1-npache@redhat.com/ > V8 : https://lore.kernel.org/lkml/20250702055742.102808-1-npache@redhat.com/ > V7 : https://lore.kernel.org/lkml/20250515032226.128900-1-npache@redhat.com/ > V6 : https://lore.kernel.org/lkml/20250515030312.125567-1-npache@redhat.com/ > V5 : https://lore.kernel.org/lkml/20250428181218.85925-1-npache@redhat.com/ > V4 : https://lore.kernel.org/lkml/20250417000238.74567-1-npache@redhat.com/ > V3 : https://lore.kernel.org/lkml/20250414220557.35388-1-npache@redhat.com/ > V2 : https://lore.kernel.org/lkml/20250211003028.213461-1-npache@redhat.com/ > V1 : https://lore.kernel.org/lkml/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 endeavour. > > [1] - https://gitlab.com/npache/khugepaged_mthp_test > [2] - https://lore.kernel.org/lkml/20250515033857.132535-1-npache@redhat.com/ > > Baolin Wang (1): > khugepaged: run khugepaged for all orders > > Dev Jain (1): > khugepaged: generalize alloc_charge_folio() > > Nico Pache (14): > khugepaged: rename hpage_collapse_* to collapse_* > introduce collapse_single_pmd to unify khugepaged and madvise_collapse > khugepaged: generalize hugepage_vma_revalidate for mTHP support > khugepaged: introduce is_mthp_order helper > khugepaged: generalize __collapse_huge_page_* for mTHP support > khugepaged: introduce collapse_max_ptes_none helper function > khugepaged: generalize collapse_huge_page for mTHP collapse > khugepaged: skip collapsing mTHP to smaller orders > khugepaged: add per-order mTHP collapse failure statistics > khugepaged: improve tracepoints for mTHP orders > khugepaged: introduce collapse_allowable_orders helper function > khugepaged: Introduce mTHP collapse support > khugepaged: avoid unnecessary mTHP collapse attempts > Documentation: mm: update the admin guide for mTHP collapse > > Documentation/admin-guide/mm/transhuge.rst | 80 ++- > include/linux/huge_mm.h | 5 + > include/trace/events/huge_memory.h | 34 +- > mm/huge_memory.c | 11 + > mm/khugepaged.c | 696 +++++++++++++++------ > mm/mremap.c | 2 +- > 6 files changed, 618 insertions(+), 210 deletions(-) > > -- > 2.51.1 >
On 12/1/25 18:46, Nico Pache wrote: > 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 limitiations 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: Refactor/rename hpage_collapse > Patch 2: Refactoring to combine madvise_collapse and khugepaged These two patches could get queued already separately, right? -- Cheers David
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