On Thu, Jan 9, 2025 at 9:56 PM Dev Jain <dev.jain@xxxxxxx> wrote: > > > > On 10/01/25 7:57 am, Nico Pache wrote: > > On Wed, Jan 8, 2025 at 11:22 PM Dev Jain <dev.jain@xxxxxxx> 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@xxxxxxx/ > >>> > >>> 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@xxxxxxxxxx/ > > > >> > > > I tested your series with the program I was using and it is not working; > can you please confirm it. Yes, this is expected because you are not fully filling any 32K chunk (MIN_MTHP_ORDER) so no bit is ever set. I should probably add some threshold to scan_pmd so we set the bitmap if at least half of the region is full or scale it on max_ptes_none like I do in scan_bitmap. Thanks for your review-- Have a good weekend! > > 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@xxxxxxx> > + * > + * 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; > +} > -- > 2.30.2 > > Set enabled = madvise, hugepages-2048k/enabled = hugepages-64k/enabled = > inherit. Run the program in the background, then run tools/mm/thpmaps. > You will see PMD collapse correctly, but when you echo never into > hugepages-2048k/enabled and test this again, you won't see contpte 64K > collapse. With my series, you will see something like > > anon-cont-pte-aligned-64kB : 32768 kB (100%). >
