| 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(-) >
On Wed, Jan 8, 2025 at 11:27 PM Dev Jain <dev.jain@arm.com> wrote: > > > 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 :) Sorry! I missed that in my initial review of your code. Seeing that would have saved me a few hours of debugging xD > > int nr_pages = folio_nr_pages(folio); > folio_ref_add(folio, nr_pages - 1); Once I found the fix I forgot to cross reference with your series. Missing this ref update was causing the issue I alluded to in your RFC thread. When you said you ran into some issues on the debug configs I figured it was the same one. > > > > > 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(-) > > >
On Wed, Jan 8, 2025 at 11:22 PM Dev Jain <dev.jain@arm.com> wrote: > > > 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? I Built these changes for the following arches: x86_64, arm64, arm64-64k, ppc64le, s390x x86 testing: - Selftests mm - some stress-ng tests - compile kernel - I did some tests with my defer [1] set on top. This pushes all the work to khugepaged, which removes the noise of all the PF allocations. I recently got an ARM64 machine and did some simple sanity tests (on both 4k and 64k) like selftests, stress-ng, and playing around with the tunables, etc. I will also be running all the builds through our CI, and perf testing environments before posting. [1] https://lore.kernel.org/lkml/20240729222727.64319-1-npache@redhat.com/ >
On 10/01/25 7:57 am, Nico Pache wrote: > On Wed, Jan 8, 2025 at 11:22 PM Dev Jain <dev.jain@arm.com> wrote: >> >> >> 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? > > I Built these changes for the following arches: x86_64, arm64, > arm64-64k, ppc64le, s390x > > x86 testing: > - Selftests mm > - some stress-ng tests > - compile kernel > - I did some tests with my defer [1] set on top. This pushes all the > work to khugepaged, which removes the noise of all the PF allocations. > > I recently got an ARM64 machine and did some simple sanity tests (on > both 4k and 64k) like selftests, stress-ng, and playing around with > the tunables, etc. > > I will also be running all the builds through our CI, and perf testing > environments before posting. > > [1] https://lore.kernel.org/lkml/20240729222727.64319-1-npache@redhat.com/ > >> > I tested your series with the program I was using and it is not working; can you please confirm it. diff --git a/mytests/mthp.c b/mytests/mthp.c new file mode 100644 index 000000000000..e3029dbcf035 --- /dev/null +++ b/mytests/mthp.c @@ -0,0 +1,45 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * + * Author: Dev Jain <dev.jain@arm.com> + * + * Program to test khugepaged mTHP collapse + */ + +#include <unistd.h> +#include <sys/ioctl.h> +#include <string.h> +#include <stdint.h> +#include <stdlib.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/mman.h> +#include <sys/time.h> +#include <sys/random.h> +#include <assert.h> + +int main(int argc, char *argv[]) +{ + char *ptr; + unsigned long mthp_size = (1UL << 16); + size_t chunk_size = (1UL << 25); + + ptr = mmap((void *)(1UL << 30), chunk_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (((unsigned long)ptr) != (1UL << 30)) { + printf("mmap did not work on required address\n"); + return 1; + } + + /* Fill first pte in every 64K interval */ + for (int i = 0; i < chunk_size; i += mthp_size) + ptr[i] = i; + + if (madvise(ptr, chunk_size, MADV_HUGEPAGE)) { + perror("madvise"); + return 1; + } + sleep(100); + return 0; +}
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(-)