On Wed, Sep 6, 2023 at 7:26 AM Usama Arif <[email protected]> wrote:
>
> This series moves the boot time initialization of tail struct pages of a
> gigantic page to later on in the boot. Only the
> HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page) - 1 tail struct pages
> are initialized at the start. If HVO is successful, then no more tail struct
> pages need to be initialized. For a 1G hugepage, this series avoid
> initialization of 262144 - 63 = 262081 struct pages per hugepage.
>
> When tested on a 512G system (which can allocate max 500 1G hugepages), the
> kexec-boot time with HVO and DEFERRED_STRUCT_PAGE_INIT enabled without this
> patchseries to running init is 3.9 seconds. With this patch it is 1.2 seconds.
> This represents an approximately 70% reduction in boot time and will
> significantly reduce server downtime when using a large number of
> gigantic pages.
My use case is different, but this patch series benefits it. I have a
virtual machines with a large number of hugetlb pages. The RSS size of
the VM after boot is much smaller with this series:
Before: 9G
After: 600M
The VM has 500 1G pages, and 512G total RAM. I would add this to the
description, that this series can help reduce the VM overhead and boot
performance for those who are using hugetlb pages in the VMs.
Also, DEFERRED_STRUCT_PAGE_INIT is a requirement for this series to
work, and should be added into documentation.
Pasha
> Thanks,
> Usama
>
> [v3->v4]:
> - rebase ontop of patch "hugetlb: set hugetlb page flag before optimizing vmemmap".
> - freeze head struct page ref count.
> - Change order of operations to initialize head struct page -> initialize
> the necessary tail struct pages -> attempt HVO -> initialize the rest of the
> tail struct pages if HVO fails.
> - (Mike Rapoport and Muchun Song) remove "_vmemmap" suffix from memblock reserve
> noinit flags anf functions.
>
> [v2->v3]:
> - (Muchun Song) skip prep of struct pages backing gigantic hugepages
> at boot time only.
> - (Muchun Song) move initialization of tail struct pages to after
> HVO is attempted.
>
> [v1->v2]:
> - (Mike Rapoport) Code quality improvements (function names, arguments,
> comments).
>
> [RFC->v1]:
> - (Mike Rapoport) Change from passing hugepage_size in
> memblock_alloc_try_nid_raw for skipping struct page initialization to
> using MEMBLOCK_RSRV_NOINIT flag
>
> Usama Arif (4):
> mm: hugetlb_vmemmap: Use nid of the head page to reallocate it
> memblock: pass memblock_type to memblock_setclr_flag
> memblock: introduce MEMBLOCK_RSRV_NOINIT flag
> mm: hugetlb: Skip initialization of gigantic tail struct pages if
> freed by HVO
>
> include/linux/memblock.h | 9 ++++++
> mm/hugetlb.c | 61 ++++++++++++++++++++++++++++++++++------
> mm/hugetlb_vmemmap.c | 4 +--
> mm/hugetlb_vmemmap.h | 9 +++---
> mm/internal.h | 3 ++
> mm/memblock.c | 48 ++++++++++++++++++++++---------
> mm/mm_init.c | 2 +-
> 7 files changed, 107 insertions(+), 29 deletions(-)
>
> --
> 2.25.1
>
>