On Wed, Sep 6, 2023 at 7:26 AM Usama Arif <usama.arif@xxxxxxxxxxxxx> 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 > >
