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SubjectRe: [RFC REBASED 5/5] powerpc/mm/slice: use the dynamic high slice size to limit bitmap operations
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Le 28/02/2018 à 07:53, Nicholas Piggin a écrit :
> On Tue, 27 Feb 2018 18:11:07 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
>
>> Nicholas Piggin <npiggin@gmail.com> writes:
>>
>>> On Tue, 27 Feb 2018 14:31:07 +0530
>>> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
>>>
>>>> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>>>>
>>>>> The number of high slices a process might use now depends on its
>>>>> address space size, and what allocation address it has requested.
>>>>>
>>>>> This patch uses that limit throughout call chains where possible,
>>>>> rather than use the fixed SLICE_NUM_HIGH for bitmap operations.
>>>>> This saves some cost for processes that don't use very large address
>>>>> spaces.
>>>>
>>>> I haven't really looked at the final code. One of the issue we had was
>>>> with the below scenario.
>>>>
>>>> mmap(addr, len) where addr < 128TB and addr+len > 128TB We want to make
>>>> sure we build the mask such that we don't find the addr available.
>>>
>>> We should run it through the mmap regression tests. I *think* we moved
>>> all of that logic from the slice code to get_ummapped_area before going
>>> in to slices. I may have missed something though, it would be good to
>>> have more eyes on it.
>>>
>>
>> mmap(-1,...) failed with the test. Something like below fix it
>>
>> @@ -756,7 +770,7 @@ void slice_set_user_psize(struct mm_struct *mm, unsigned int psize)
>> mm->context.low_slices_psize = lpsizes;
>>
>> hpsizes = mm->context.high_slices_psize;
>> - high_slices = GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit);
>> + high_slices = SLICE_NUM_HIGH;
>> for (i = 0; i < high_slices; i++) {
>> mask_index = i & 0x1;
>> index = i >> 1;
>>
>> I guess for everything in the mm_context_t, we should compute it till
>> SLICE_NUM_HIGH. The reason for failure was, even though we recompute the
>> slice mask cached in mm_context on slb_addr_limit, it was still derived
>> from the high_slices_psizes which was computed with lower value.
>
> Okay thanks for catching that Aneesh. I guess that's a slow path so it
> should be okay. Christophe if you're taking care of the series can you
> fold it in? Otherwise I'll do that after yours gets merged.
>

I'm not really taking care of your serie, just took it once to see how
it fits on the 8xx.
I prefer if you can handle them. If you need my help for any test on
PPC32 don't hesitate to ask.

Christophe

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