Messages in this thread | | | Subject | Re: [RFC REBASED 5/5] powerpc/mm/slice: use the dynamic high slice size to limit bitmap operations | From | "Aneesh Kumar K.V" <> | Date | Wed, 28 Feb 2018 12:29:52 +0530 |
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On 02/28/2018 12:23 PM, Nicholas Piggin wrote: > 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. >
should we also compute the mm_context_t.slice_mask using SLICE_NUM_HIGH and skip the recalc_slice_mask_cache when we change the addr limit?
-aneesh
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