On Mon, 18 May 2020 13:08:49 +0800 Bibo Mao <maob...@loongson.cn> wrote:
> On mips platform, hw PTE entry valid bit is set in pte_mkyoung > function, it is used to set physical page with readable privilege. pte_mkyoung() seems to be a strange place to set the pte's valid bit. Why is it done there? Can it be done within mips's mk_pte()? > Here add pte_mkyoung function to make page readable on MIPS platform > during page fault handling. This patch improves page fault latency > about 10% on my MIPS machine with lmbench lat_pagefault case. > > ... > > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2704,6 +2704,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) > } > flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); > entry = mk_pte(new_page, vma->vm_page_prot); > + entry = pte_mkyoung(entry); > entry = maybe_mkwrite(pte_mkdirty(entry), vma); What is the effect on non-mips machines? If it's only "additional overhead" then it would be better to add a new pte_mkvalid() (or whatever) and arrange for it to be a no-op on all but mips? > /* > * Clear the pte entry and flush it first, before updating the > @@ -3378,6 +3379,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault > *vmf) > __SetPageUptodate(page); > > entry = mk_pte(page, vma->vm_page_prot); > + entry = pte_mkyoung(entry); > if (vma->vm_flags & VM_WRITE) > entry = pte_mkwrite(pte_mkdirty(entry)); > > @@ -3660,6 +3662,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct > mem_cgroup *memcg, > > flush_icache_page(vma, page); > entry = mk_pte(page, vma->vm_page_prot); > + entry = pte_mkyoung(entry); > if (write) > entry = maybe_mkwrite(pte_mkdirty(entry), vma); > /* copy-on-write page */ > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 494192ca..673f1cd 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -131,6 +131,8 @@ static unsigned long change_pte_range(struct > vm_area_struct *vma, pmd_t *pmd, > ptent = pte_clear_uffd_wp(ptent); > } > > + if (vma->vm_flags & VM_READ) > + ptent = pte_mkyoung(ptent); > /* Avoid taking write faults for known dirty pages */ > if (dirty_accountable && pte_dirty(ptent) && > (pte_soft_dirty(ptent) ||
