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On 5/13/19 7:01 PM, Nadav Amit wrote:
On May 13, 2019 4:01 PM, Yang Shi
<yang.shi@xxxxxxxxxxxxxxxxx> wrote:
On 5/13/19 9:38 AM, Will Deacon wrote:
> On Fri, May 10, 2019 at 07:26:54AM +0800,
Yang Shi wrote:
>> diff --git a/mm/mmu_gather.c
b/mm/mmu_gather.c
>> index 99740e1..469492d 100644
>> --- a/mm/mmu_gather.c
>> +++ b/mm/mmu_gather.c
>> @@ -245,14 +245,39 @@ void
tlb_finish_mmu(struct mmu_gather *tlb,
>> {
>> /*
>> * If there are parallel threads
are doing PTE changes on same range
>> - * under non-exclusive lock(e.g.,
mmap_sem read-side) but defer TLB
>> - * flush by batching, a thread has
stable TLB entry can fail to flush
>> - * the TLB by observing
pte_none|!pte_dirty, for example so flush TLB
>> - * forcefully if we detect parallel
PTE batching threads.
>> + * under non-exclusive lock (e.g.,
mmap_sem read-side) but defer TLB
>> + * flush by batching, one thread may
end up seeing inconsistent PTEs
>> + * and result in having stale TLB
entries. So flush TLB forcefully
>> + * if we detect parallel PTE
batching threads.
>> + *
>> + * However, some syscalls, e.g.
munmap(), may free page tables, this
>> + * needs force flush everything in
the given range. Otherwise this
>> + * may result in having stale TLB
entries for some architectures,
>> + * e.g. aarch64, that could specify
flush what level TLB.
>> */
>> - if (mm_tlb_flush_nested(tlb->mm))
{
>> - __tlb_reset_range(tlb);
>> - __tlb_adjust_range(tlb,
start, end - start);
>> + if (mm_tlb_flush_nested(tlb->mm)
&& !tlb->fullmm) {
>> + /*
>> + * Since we can't tell what
we actually should have
>> + * flushed, flush everything
in the given range.
>> + */
>> + tlb->freed_tables = 1;
>> + tlb->cleared_ptes = 1;
>> + tlb->cleared_pmds = 1;
>> + tlb->cleared_puds = 1;
>> + tlb->cleared_p4ds = 1;
>> +
>> + /*
>> + * Some architectures, e.g.
ARM, that have range invalidation
>> + * and care about VM_EXEC
for I-Cache invalidation, need force
>> + * vma_exec set.
>> + */
>> + tlb->vma_exec = 1;
>> +
>> + /* Force vma_huge clear to
guarantee safer flush */
>> + tlb->vma_huge = 0;
>> +
>> + tlb->start = start;
>> + tlb->end = end;
>> }
> Whilst I think this is correct, it would be
interesting to see whether
> or not it's actually faster than just nuking
the whole mm, as I mentioned
> before.
>
> At least in terms of getting a short-term
fix, I'd prefer the diff below
> if it's not measurably worse.
I did a quick test with ebizzy (96 threads with 5
iterations) on my x86
VM, it shows slightly slowdown on records/s but
much more sys time spent
with fullmm flush, the below is the data.
nofullmm fullmm
ops (records/s)
225606 225119
sys (s)
0.69 1.14
It looks the slight reduction of records/s is
caused by the increase of
sys time.
>
> Will
>
> --->8
>
> diff --git a/mm/mmu_gather.c
b/mm/mmu_gather.c
> index 99740e1dd273..cc251422d307 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -251,8 +251,9 @@ void
tlb_finish_mmu(struct mmu_gather *tlb,
> * forcefully if we detect parallel
PTE batching threads.
> */
> if (mm_tlb_flush_nested(tlb->mm)) {
> + tlb->fullmm = 1;
> __tlb_reset_range(tlb);
> - __tlb_adjust_range(tlb, start,
end - start);
> + tlb->freed_tables = 1;
> }
>
> tlb_flush_mmu(tlb);
I think that this should have set need_flush_all
and not fullmm.
Thanks for the suggestion. I did a quick test with ebizzy too. It
looks this is almost same with the v2 patch and slightly better than
what Will suggested.
nofullmm fullmm need_flush_all
ops (records/s) 225606
225119 225647
sys (s) 0.69
1.14 0.47
If no objection from other folks, I would respin the patch based
off Nadav's suggestion.
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