On Wed, Sep 02, 2020 at 02:06:12PM -0400, Zi Yan wrote: > From: Zi Yan <ziy@xxxxxxxxxx> > > Hi all, > > This patchset adds support for 1GB THP on x86_64. It is on top of > v5.9-rc2-mmots-2020-08-25-21-13. > > 1GB THP is more flexible for reducing translation overhead and increasing the > performance of applications with large memory footprint without application > changes compared to hugetlb. > > Design > ======= > > 1GB THP implementation looks similar to exiting THP code except some new designs > for the additional page table level. > > 1. Page table deposit and withdraw using a new pagechain data structure: > instead of one PTE page table page, 1GB THP requires 513 page table pages > (one PMD page table page and 512 PTE page table pages) to be deposited > at the page allocaiton time, so that we can split the page later. Currently, > the page table deposit is using ->lru, thus only one page can be deposited. > A new pagechain data structure is added to enable multi-page deposit. > > 2. Triple mapped 1GB THP : 1GB THP can be mapped by a combination of PUD, PMD, > and PTE entries. Mixing PUD an PTE mapping can be achieved with existing > PageDoubleMap mechanism. To add PMD mapping, PMDPageInPUD and > sub_compound_mapcount are introduced. PMDPageInPUD is the 512-aligned base > page in a 1GB THP and sub_compound_mapcount counts the PMD mapping by using > page[N*512 + 3].compound_mapcount. > > 3. Using CMA allocaiton for 1GB THP: instead of bump MAX_ORDER, it is more sane > to use something less intrusive. So all 1GB THPs are allocated from reserved > CMA areas shared with hugetlb. At page splitting time, the bitmap for the 1GB > THP is cleared as the resulting pages can be freed via normal page free path. > We can fall back to alloc_contig_pages for 1GB THP if necessary. > > > Patch Organization > ======= > > Patch 01 adds the new pagechain data structure. > > Patch 02 to 13 adds 1GB THP support in variable places. > > Patch 14 tries to use alloc_contig_pages for 1GB THP allocaiton. > > Patch 15 moves hugetlb_cma reservation to cma.c and rename it to hugepage_cma. > > Patch 16 use hugepage_cma reservation for 1GB THP allocation. > > > Any suggestions and comments are welcome. > > > Zi Yan (16): > mm: add pagechain container for storing multiple pages. > mm: thp: 1GB anonymous page implementation. > mm: proc: add 1GB THP kpageflag. > mm: thp: 1GB THP copy on write implementation. > mm: thp: handling 1GB THP reference bit. > mm: thp: add 1GB THP split_huge_pud_page() function. > mm: stats: make smap stats understand PUD THPs. > mm: page_vma_walk: teach it about PMD-mapped PUD THP. > mm: thp: 1GB THP support in try_to_unmap(). > mm: thp: split 1GB THPs at page reclaim. > mm: thp: 1GB THP follow_p*d_page() support. > mm: support 1GB THP pagemap support. > mm: thp: add a knob to enable/disable 1GB THPs. > mm: page_alloc: >=MAX_ORDER pages allocation an deallocation. > hugetlb: cma: move cma reserve function to cma.c. > mm: thp: use cma reservation for pud thp allocation. Surprised this doesn't touch mm/pagewalk.c ? Jason
