On Tue, 27 Feb 2018 18:11:07 +0530
"Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com> wrote:
> Nicholas Piggin <npig...@gmail.com> writes:
>
> > On Tue, 27 Feb 2018 14:31:07 +0530
> > "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com> wrote:
> >
> >> Christophe Leroy <christophe.le...@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.
Thanks,
Nick
