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Message-ID: <CAJd=RBCowwbYuj3OGmGV4TfTL-q3CNKja7E+D3Xn1X7DoUVmiA@mail.gmail.com>
Date: Fri, 4 May 2012 20:22:37 +0800
From: Hillf Danton <dhillf@...il.com>
To: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATH v2 3/5] x86/tlb: fall back to flush all when meet a THP
large page
On Fri, May 4, 2012 at 8:11 PM, Hillf Danton <dhillf@...il.com> wrote:
> Hi Alex,
>
> On Fri, May 4, 2012 at 2:50 PM, Alex Shi <alex.shi@...el.com> wrote:
>> We don't need to flush large pages by PAGE_SIZE step, that just waste
>> time. and actually, large page don't need 'invlpg' optimizing according
>> to our macro benchmark. So, just flush whole TLB is enough for them.
>>
>> The following result is tested on a 2CPU * 4cores * 2HT NHM EP machine,
>> with THP 'always' setting.
>>
>> Multi-thread testing, '-t' paramter is thread number:
>> without this patch with this patch
>> ./mprotect -t 1 14ns 13ns
>> ./mprotect -t 2 13ns 13ns
>> ./mprotect -t 4 12ns 11ns
>> ./mprotect -t 8 14ns 10ns
>> ./mprotect -t 16 28ns 28ns
>> ./mprotect -t 32 54ns 52ns
>> ./mprotect -t 128 200ns 200ns
>>
>> Signed-off-by: Alex Shi <alex.shi@...el.com>
>> ---
>> arch/x86/mm/tlb.c | 27 +++++++++++++++++++++++++++
>> 1 files changed, 27 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
>> index c4e694d..4f709e6 100644
>> --- a/arch/x86/mm/tlb.c
>> +++ b/arch/x86/mm/tlb.c
>> @@ -316,12 +316,35 @@ void flush_tlb_mm(struct mm_struct *mm)
>>
>> #define FLUSHALL_BAR 16
>>
>> +static inline int has_large_page(struct mm_struct *mm,
>> + unsigned long start, unsigned long end)
>> +{
>> + pgd_t *pgd;
>> + pud_t *pud;
>> + pmd_t *pmd;
>> + unsigned long addr;
>> + for (addr = start; addr <= end; addr += HPAGE_SIZE) {
>> + pgd = pgd_offset(mm, addr);
>> + if (likely(!pgd_none(*pgd))) {
>> + pud = pud_offset(pgd, addr);
>> + if (likely(!pud_none(*pud))) {
>> + pmd = pmd_offset(pud, addr);
>> + if (likely(!pmd_none(*pmd)))
>> + if (pmd_large(*pmd))
>> + return 1;
>> + }
>> + }
>> + }
>> + return 0;
>> +}
>> +
>> void flush_tlb_range(struct vm_area_struct *vma,
>> unsigned long start, unsigned long end)
>> {
>> struct mm_struct *mm;
>>
>> if (!cpu_has_invlpg || vma->vm_flags & VM_HUGETLB) {
>> +flush_all:
>> flush_tlb_mm(vma->vm_mm);
>> return;
>> }
>> @@ -344,6 +367,10 @@ void flush_tlb_range(struct vm_area_struct *vma,
>> if ((end - start)/PAGE_SIZE > act_entries/FLUSHALL_BAR)
>> local_flush_tlb();
>> else {
>> + if (has_large_page(mm, start, end)) {
>> + preempt_enable();
>> + goto flush_all;
>> + }
>> for (addr = start; addr <= end;
>> addr += PAGE_SIZE)
>> __flush_tlb_single(addr);
>> --
>>
> Perhaps huge pages could be handled alternatively, tho dunno the
> point to flush tlb manually.
>
> --- a/x86-mm-tlb.c Fri May 4 19:53:40 2012
> +++ b/x86-mm-tlb.c Fri May 4 20:01:36 2012
> @@ -2,7 +2,7 @@ void flush_tlb_range(struct vm_area_stru
> {
> struct mm_struct *mm;
>
> - if (!cpu_has_invlpg || vma->vm_flags & VM_HUGETLB) {
> + if (!cpu_has_invlpg) {
> flush_tlb_mm(vma->vm_mm);
> return;
> }
> @@ -13,6 +13,7 @@ void flush_tlb_range(struct vm_area_stru
> if (current->mm) {
> unsigned long addr, vmflag = vma->vm_flags;
> unsigned act_entries, tlb_entries = 0;
> + unsigned long pg_sz;
>
> if (vmflag & VM_EXEC)
> tlb_entries = tlb_lli_4k[ENTRIES];
> @@ -22,11 +23,15 @@ void flush_tlb_range(struct vm_area_stru
> act_entries = tlb_entries > mm->total_vm ?
> mm->total_vm : tlb_entries;
>
> - if ((end - start)/PAGE_SIZE > act_entries/FLUSHALL_BAR)
> + pg_sz = (transparent_hugepage_enabled(vma) ||
> + is_vm_hugetlb_page(vma)) ?
> + HPAGE_SIZE : PAGE_SIZE;
> +
> + if ((end - start)/pg_sz > act_entries/FLUSHALL_BAR)
> local_flush_tlb();
> else {
> for (addr = start; addr <= end;
> - addr += PAGE_SIZE)
> + addr += pg_sz)
> __flush_tlb_single(addr);
>
> if (cpumask_any_but(mm_cpumask(mm),
> --
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