| Message ID | 20250108233128.14484-1-npache@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | khugepaged: mTHP support | expand |
On 09/01/25 5:01 am, Nico Pache wrote: > The following series provides khugepaged and madvise collapse with the > capability to collapse regions to mTHPs. > > To achieve this we generalize the khugepaged functions to no longer depend > on PMD_ORDER. Then during the PMD scan, we keep track of chunks of pages > (defined by MTHP_MIN_ORDER) that are fully utilized. This info is tracked > using a bitmap. After the PMD scan is done, we do binary recursion on 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. max_ptes_none is mapped to a 0-100 range to > determine how full a mTHP order needs to be before collapsing it. > > Some design choices to note: > - bitmap structures are allocated dynamically because on some arch's > (like PowerPC) the value of MTHP_BITMAP_SIZE cannot be computed at > compile time leading to warnings. > - The recursion is masked through a stack structure. > - A MTHP_MIN_ORDER was added to compress the bitmap, and ensure it was > 64bit on x86. This provides some optimization on the bitmap operations. > if other arches/configs that have larger than 512 PTEs per PMD want to > compress their bitmap further we can change this value per arch. > > Patch 1-2: Some refactoring to combine madvise_collapse and khugepaged > Patch 3: A minor "fix"/optimization > Patch 4: Refactor/rename hpage_collapse > Patch 5-7: Generalize khugepaged functions for arbitrary orders > Patch 8-11: The mTHP patches > > This series acts as an alternative to Dev Jain's approach [1]. The two > series differ in a few ways: > - My approach uses a bitmap to store the state of the linear scan_pmd to > then determine potential mTHP batches. Devs incorporates his directly > into the scan, and will try each available order. > - Dev is attempting to optimize the locking, while my approach keeps the > locking changes to a minimum. I believe his changes are not safe for > uffd. > - Dev's changes only work for khugepaged not madvise_collapse (although > i think that was by choice and it could easily support madvise) > - Dev scales all khugepaged sysfs tunables by order, while im removing > the restriction of max_ptes_none and converting it to a scale to > determine a (m)THP threshold. > - Dev turns on khugepaged if any order is available while mine still > only runs if PMDs are enabled. I like Dev's approach and will most > likely do the same in my PATCH posting. > - mTHPs need their ref count updated to 1<<order, which Dev is missing. > > Patch 11 was inspired by one of Dev's changes. > > [1] https://lore.kernel.org/lkml/20241216165105.56185-1-dev.jain@arm.com/ > > Nico Pache (11): > introduce khugepaged_collapse_single_pmd to collapse a single pmd > khugepaged: refactor madvise_collapse and khugepaged_scan_mm_slot > khugepaged: Don't allocate khugepaged mm_slot early > khugepaged: rename hpage_collapse_* to khugepaged_* > khugepaged: generalize hugepage_vma_revalidate for mTHP support > khugepaged: generalize alloc_charge_folio for mTHP support > khugepaged: generalize __collapse_huge_page_* for mTHP support > khugepaged: introduce khugepaged_scan_bitmap for mTHP support > khugepaged: add mTHP support > khugepaged: remove max_ptes_none restriction on the pmd scan > khugepaged: skip collapsing mTHP to smaller orders > > include/linux/khugepaged.h | 4 +- > mm/huge_memory.c | 3 +- > mm/khugepaged.c | 436 +++++++++++++++++++++++++------------ > 3 files changed, 306 insertions(+), 137 deletions(-) Before I take a proper look at your series, can you please include any testing you may have done?
On 09/01/25 5:01 am, Nico Pache wrote: > The following series provides khugepaged and madvise collapse with the > capability to collapse regions to mTHPs. > > To achieve this we generalize the khugepaged functions to no longer depend > on PMD_ORDER. Then during the PMD scan, we keep track of chunks of pages > (defined by MTHP_MIN_ORDER) that are fully utilized. This info is tracked > using a bitmap. After the PMD scan is done, we do binary recursion on 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. max_ptes_none is mapped to a 0-100 range to > determine how full a mTHP order needs to be before collapsing it. > > Some design choices to note: > - bitmap structures are allocated dynamically because on some arch's > (like PowerPC) the value of MTHP_BITMAP_SIZE cannot be computed at > compile time leading to warnings. > - The recursion is masked through a stack structure. > - A MTHP_MIN_ORDER was added to compress the bitmap, and ensure it was > 64bit on x86. This provides some optimization on the bitmap operations. > if other arches/configs that have larger than 512 PTEs per PMD want to > compress their bitmap further we can change this value per arch. > > Patch 1-2: Some refactoring to combine madvise_collapse and khugepaged > Patch 3: A minor "fix"/optimization > Patch 4: Refactor/rename hpage_collapse > Patch 5-7: Generalize khugepaged functions for arbitrary orders > Patch 8-11: The mTHP patches > > This series acts as an alternative to Dev Jain's approach [1]. The two > series differ in a few ways: > - My approach uses a bitmap to store the state of the linear scan_pmd to > then determine potential mTHP batches. Devs incorporates his directly > into the scan, and will try each available order. > - Dev is attempting to optimize the locking, while my approach keeps the > locking changes to a minimum. I believe his changes are not safe for > uffd. > - Dev's changes only work for khugepaged not madvise_collapse (although > i think that was by choice and it could easily support madvise) > - Dev scales all khugepaged sysfs tunables by order, while im removing > the restriction of max_ptes_none and converting it to a scale to > determine a (m)THP threshold. > - Dev turns on khugepaged if any order is available while mine still > only runs if PMDs are enabled. I like Dev's approach and will most > likely do the same in my PATCH posting. > - mTHPs need their ref count updated to 1<<order, which Dev is missing. Well, I did not miss it :) int nr_pages = folio_nr_pages(folio); folio_ref_add(folio, nr_pages - 1); > > Patch 11 was inspired by one of Dev's changes. > > [1] https://lore.kernel.org/lkml/20241216165105.56185-1-dev.jain@arm.com/ > > Nico Pache (11): > introduce khugepaged_collapse_single_pmd to collapse a single pmd > khugepaged: refactor madvise_collapse and khugepaged_scan_mm_slot > khugepaged: Don't allocate khugepaged mm_slot early > khugepaged: rename hpage_collapse_* to khugepaged_* > khugepaged: generalize hugepage_vma_revalidate for mTHP support > khugepaged: generalize alloc_charge_folio for mTHP support > khugepaged: generalize __collapse_huge_page_* for mTHP support > khugepaged: introduce khugepaged_scan_bitmap for mTHP support > khugepaged: add mTHP support > khugepaged: remove max_ptes_none restriction on the pmd scan > khugepaged: skip collapsing mTHP to smaller orders > > include/linux/khugepaged.h | 4 +- > mm/huge_memory.c | 3 +- > mm/khugepaged.c | 436 +++++++++++++++++++++++++------------ > 3 files changed, 306 insertions(+), 137 deletions(-) >
The following series provides khugepaged and madvise collapse with the capability to collapse regions to mTHPs. To achieve this we generalize the khugepaged functions to no longer depend on PMD_ORDER. Then during the PMD scan, we keep track of chunks of pages (defined by MTHP_MIN_ORDER) that are fully utilized. This info is tracked using a bitmap. After the PMD scan is done, we do binary recursion on 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. max_ptes_none is mapped to a 0-100 range to determine how full a mTHP order needs to be before collapsing it. Some design choices to note: - bitmap structures are allocated dynamically because on some arch's (like PowerPC) the value of MTHP_BITMAP_SIZE cannot be computed at compile time leading to warnings. - The recursion is masked through a stack structure. - A MTHP_MIN_ORDER was added to compress the bitmap, and ensure it was 64bit on x86. This provides some optimization on the bitmap operations. if other arches/configs that have larger than 512 PTEs per PMD want to compress their bitmap further we can change this value per arch. Patch 1-2: Some refactoring to combine madvise_collapse and khugepaged Patch 3: A minor "fix"/optimization Patch 4: Refactor/rename hpage_collapse Patch 5-7: Generalize khugepaged functions for arbitrary orders Patch 8-11: The mTHP patches This series acts as an alternative to Dev Jain's approach [1]. The two series differ in a few ways: - My approach uses a bitmap to store the state of the linear scan_pmd to then determine potential mTHP batches. Devs incorporates his directly into the scan, and will try each available order. - Dev is attempting to optimize the locking, while my approach keeps the locking changes to a minimum. I believe his changes are not safe for uffd. - Dev's changes only work for khugepaged not madvise_collapse (although i think that was by choice and it could easily support madvise) - Dev scales all khugepaged sysfs tunables by order, while im removing the restriction of max_ptes_none and converting it to a scale to determine a (m)THP threshold. - Dev turns on khugepaged if any order is available while mine still only runs if PMDs are enabled. I like Dev's approach and will most likely do the same in my PATCH posting. - mTHPs need their ref count updated to 1<<order, which Dev is missing. Patch 11 was inspired by one of Dev's changes. [1] https://lore.kernel.org/lkml/20241216165105.56185-1-dev.jain@arm.com/ Nico Pache (11): introduce khugepaged_collapse_single_pmd to collapse a single pmd khugepaged: refactor madvise_collapse and khugepaged_scan_mm_slot khugepaged: Don't allocate khugepaged mm_slot early khugepaged: rename hpage_collapse_* to khugepaged_* khugepaged: generalize hugepage_vma_revalidate for mTHP support khugepaged: generalize alloc_charge_folio for mTHP support khugepaged: generalize __collapse_huge_page_* for mTHP support khugepaged: introduce khugepaged_scan_bitmap for mTHP support khugepaged: add mTHP support khugepaged: remove max_ptes_none restriction on the pmd scan khugepaged: skip collapsing mTHP to smaller orders include/linux/khugepaged.h | 4 +- mm/huge_memory.c | 3 +- mm/khugepaged.c | 436 +++++++++++++++++++++++++------------ 3 files changed, 306 insertions(+), 137 deletions(-)