Messages in this thread | | | Date | Tue, 19 Sep 2023 14:27:44 +0800 | Subject | Re: [PATCH v4 6/8] hugetlb: batch PMD split for bulk vmemmap dedup | From | Muchun Song <> |
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On 2023/9/19 07:01, Mike Kravetz wrote: > From: Joao Martins <joao.m.martins@oracle.com> > > In an effort to minimize amount of TLB flushes, batch all PMD splits > belonging to a range of pages in order to perform only 1 (global) TLB > flush. > > Add a flags field to the walker and pass whether it's a bulk allocation > or just a single page to decide to remap. First value > (VMEMMAP_SPLIT_NO_TLB_FLUSH) designates the request to not do the TLB > flush when we split the PMD. > > Rebased and updated by Mike Kravetz > > Signed-off-by: Joao Martins <joao.m.martins@oracle.com> > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> > --- > mm/hugetlb_vmemmap.c | 79 +++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 75 insertions(+), 4 deletions(-) > > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > index 147ed15bcae4..e8bc2f7567db 100644 > --- a/mm/hugetlb_vmemmap.c > +++ b/mm/hugetlb_vmemmap.c > @@ -27,6 +27,7 @@ > * @reuse_addr: the virtual address of the @reuse_page page. > * @vmemmap_pages: the list head of the vmemmap pages that can be freed > * or is mapped from. > + * @flags: used to modify behavior in bulk operations > */ > struct vmemmap_remap_walk { > void (*remap_pte)(pte_t *pte, unsigned long addr, > @@ -35,9 +36,11 @@ struct vmemmap_remap_walk { > struct page *reuse_page; > unsigned long reuse_addr; > struct list_head *vmemmap_pages; > +#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
Please add a brief comment following this macro to explain what's the behavior.
> + unsigned long flags; > }; > > -static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start) > +static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start, bool flush) > { > pmd_t __pmd; > int i; > @@ -80,7 +83,8 @@ static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start) > /* Make pte visible before pmd. See comment in pmd_install(). */ > smp_wmb(); > pmd_populate_kernel(&init_mm, pmd, pgtable); > - flush_tlb_kernel_range(start, start + PMD_SIZE); > + if (flush) > + flush_tlb_kernel_range(start, start + PMD_SIZE); > } else { > pte_free_kernel(&init_mm, pgtable); > } > @@ -127,11 +131,20 @@ static int vmemmap_pmd_range(pud_t *pud, unsigned long addr, > do { > int ret; > > - ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK); > + ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK, > + walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH);
!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH)?
Thanks.
> if (ret) > return ret; > > next = pmd_addr_end(addr, end); > + > + /* > + * We are only splitting, not remapping the hugetlb vmemmap > + * pages. > + */ > + if (!walk->remap_pte) > + continue; > + > vmemmap_pte_range(pmd, addr, next, walk); > } while (pmd++, addr = next, addr != end); > > @@ -198,7 +211,8 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end, > return ret; > } while (pgd++, addr = next, addr != end); > > - flush_tlb_kernel_range(start, end); > + if (walk->remap_pte) > + flush_tlb_kernel_range(start, end); > > return 0; > } > @@ -300,6 +314,36 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr, > set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot)); > } > > +/** > + * vmemmap_remap_split - split the vmemmap virtual address range [@start, @end) > + * backing PMDs of the directmap into PTEs > + * @start: start address of the vmemmap virtual address range that we want > + * to remap. > + * @end: end address of the vmemmap virtual address range that we want to > + * remap. > + * @reuse: reuse address. > + * > + * Return: %0 on success, negative error code otherwise. > + */ > +static int vmemmap_remap_split(unsigned long start, unsigned long end, > + unsigned long reuse) > +{ > + int ret; > + struct vmemmap_remap_walk walk = { > + .remap_pte = NULL, > + .flags = VMEMMAP_SPLIT_NO_TLB_FLUSH, > + }; > + > + /* See the comment in the vmemmap_remap_free(). */ > + BUG_ON(start - reuse != PAGE_SIZE); > + > + mmap_read_lock(&init_mm); > + ret = vmemmap_remap_range(reuse, end, &walk); > + mmap_read_unlock(&init_mm); > + > + return ret; > +} > + > /** > * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end) > * to the page which @reuse is mapped to, then free vmemmap > @@ -323,6 +367,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end, > .remap_pte = vmemmap_remap_pte, > .reuse_addr = reuse, > .vmemmap_pages = vmemmap_pages, > + .flags = 0, > }; > int nid = page_to_nid((struct page *)reuse); > gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN; > @@ -371,6 +416,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end, > .remap_pte = vmemmap_restore_pte, > .reuse_addr = reuse, > .vmemmap_pages = vmemmap_pages, > + .flags = 0, > }; > > vmemmap_remap_range(reuse, end, &walk); > @@ -422,6 +468,7 @@ static int vmemmap_remap_alloc(unsigned long start, unsigned long end, > .remap_pte = vmemmap_restore_pte, > .reuse_addr = reuse, > .vmemmap_pages = &vmemmap_pages, > + .flags = 0, > }; > > /* See the comment in the vmemmap_remap_free(). */ > @@ -630,11 +677,35 @@ void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head) > free_vmemmap_page_list(&vmemmap_pages); > } > > +static void hugetlb_vmemmap_split(const struct hstate *h, struct page *head) > +{ > + unsigned long vmemmap_start = (unsigned long)head, vmemmap_end; > + unsigned long vmemmap_reuse; > + > + if (!vmemmap_should_optimize(h, head)) > + return; > + > + vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h); > + vmemmap_reuse = vmemmap_start; > + vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE; > + > + /* > + * Split PMDs on the vmemmap virtual address range [@vmemmap_start, > + * @vmemmap_end] > + */ > + vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse); > +} > + > void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list) > { > struct folio *folio; > LIST_HEAD(vmemmap_pages); > > + list_for_each_entry(folio, folio_list, lru) > + hugetlb_vmemmap_split(h, &folio->page); > + > + flush_tlb_all(); > + > list_for_each_entry(folio, folio_list, lru) { > int ret = __hugetlb_vmemmap_optimize(h, &folio->page, > &vmemmap_pages);
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