On Tue, 6 Mar 2018 16:02:20 +0100
Christophe LEROY <christophe.le...@c-s.fr> wrote:
> Le 06/03/2018 à 14:25, Nicholas Piggin a écrit :
> > 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.
> >
> > Perormance numbers aren't changed significantly, this may change
> > with larger address spaces or different mmap access patterns that
> > require more slice mask building.
> >
> > Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> > ---
> > arch/powerpc/mm/slice.c | 75
> > +++++++++++++++++++++++++++++--------------------
> > 1 file changed, 45 insertions(+), 30 deletions(-)
> >
> > diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> > index 086c31b8b982..507d17e2cfcd 100644
> > --- a/arch/powerpc/mm/slice.c
> > +++ b/arch/powerpc/mm/slice.c
> > @@ -61,14 +61,12 @@ static void slice_print_mask(const char *label, const
> > struct slice_mask *mask) {
> > #endif
> >
> > static void slice_range_to_mask(unsigned long start, unsigned long len,
> > - struct slice_mask *ret)
> > + struct slice_mask *ret,
> > + unsigned long high_slices)
> > {
> > unsigned long end = start + len - 1;
> >
> > ret->low_slices = 0;
> > - if (SLICE_NUM_HIGH)
> > - bitmap_zero(ret->high_slices, SLICE_NUM_HIGH);
> > -
> > if (start < SLICE_LOW_TOP) {
> > unsigned long mend = min(end,
> > (unsigned long)(SLICE_LOW_TOP - 1));
> > @@ -77,6 +75,10 @@ static void slice_range_to_mask(unsigned long start,
> > unsigned long len,
> > - (1u << GET_LOW_SLICE_INDEX(start));
> > }
> >
> > + if (!SLICE_NUM_HIGH)
> > + return;
> > +
> > + bitmap_zero(ret->high_slices, high_slices);
>
> In include/linux/bitmap.h, it is said:
>
> * Note that nbits should be always a compile time evaluable constant.
> * Otherwise many inlines will generate horrible code.
>
> Not sure that's true, but it is written ...
Good question, I'll check that.
> > static inline void slice_or_mask(struct slice_mask *dst,
> > const struct slice_mask *src1,
> > - const struct slice_mask *src2)
> > + const struct slice_mask *src2,
> > + unsigned long high_slices)
> > {
> > dst->low_slices = src1->low_slices | src2->low_slices;
> > if (!SLICE_NUM_HIGH)
> > return;
> > - bitmap_or(dst->high_slices, src1->high_slices, src2->high_slices,
> > SLICE_NUM_HIGH);
> > + bitmap_or(dst->high_slices, src1->high_slices, src2->high_slices,
> > + high_slices);
>
> Why a new line here, this line is shorter than before.
> Or that was forgotten in a previous patch ?
Yeah it was previously a longer line. I will fix those.
> > @@ -643,17 +652,17 @@ unsigned long slice_get_unmapped_area(unsigned long
> > addr, unsigned long len,
> > if (addr == -ENOMEM)
> > return -ENOMEM;
> >
> > - slice_range_to_mask(addr, len, &potential_mask);
> > + slice_range_to_mask(addr, len, &potential_mask, high_slices);
> > slice_dbg(" found potential area at 0x%lx\n", addr);
> > slice_print_mask(" mask", &potential_mask);
> >
> > convert:
> > - slice_andnot_mask(&potential_mask, &potential_mask, &good_mask);
> > + slice_andnot_mask(&potential_mask, &potential_mask, &good_mask,
> > high_slices);
> > if (compat_maskp && !fixed)
> > - slice_andnot_mask(&potential_mask, &potential_mask,
> > compat_maskp);
> > + slice_andnot_mask(&potential_mask, &potential_mask,
> > compat_maskp, high_slices);
> > if (potential_mask.low_slices ||
> > (SLICE_NUM_HIGH &&
> > - !bitmap_empty(potential_mask.high_slices, SLICE_NUM_HIGH))) {
> > + !bitmap_empty(potential_mask.high_slices, high_slices))) {
>
> Are we sure high_slices is not nul here when SLICE_NUM_HIGH is not nul ?
On 64/s it should be for 64-bit processes, but perhaps not 32. I have
to look into that, so another good catch.
Perhaps I will leave this patch off the series for now because I didn't
measure much difference. Aneesh wants to expand address space even more,
so I might revisit after his patches go in, to see if the optimistation
becomes worthwhile.
Thanks,
Nick
