linux-kernel - Re: [PATCH V2 4/4] riscv: mm: Optimize TASK

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Date: Fri, 22 Dec 2023 19:25:16 +0800
From: Guo Ren <guoren@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: linux-kernel@...r.kernel.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	alexghiti@...osinc.com, charlie@...osinc.com, xiao.w.wang@...el.com, 
	david@...hat.com, panqinglin2020@...as.ac.cn, rick.p.edgecombe@...el.com, 
	willy@...radead.org, bjorn@...osinc.com, conor.dooley@...rochip.com, 
	cleger@...osinc.com, linux-riscv@...ts.infradead.org, 
	Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V2 4/4] riscv: mm: Optimize TASK_SIZE definition

On Fri, Dec 22, 2023 at 1:09 PM Leonardo Bras <leobras@...hat.com> wrote:
>
> On Thu, Dec 21, 2023 at 10:47:01AM -0500, guoren@...nel.org wrote:
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > Unify the TASK_SIZE definition with VA_BITS for better readability.
> > Add COMPAT mode user address space info in the comment.
> >
> > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@...nel.org>
> > ---
> >  arch/riscv/include/asm/pgtable.h | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index e415582276ec..d165ddae3b42 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -866,6 +866,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> >   * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> >   * Task size is:
> >   * -        0x9fc00000       (~2.5GB) for RV32.
> > + * -        0x80000000       (   2GB) for RV64 compat mode
> >   * -      0x4000000000       ( 256GB) for RV64 using SV39 mmu
> >   * -    0x800000000000       ( 128TB) for RV64 using SV48 mmu
> >   * - 0x100000000000000       (  64PB) for RV64 using SV57 mmu
> > @@ -877,11 +878,11 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> >   * Similarly for SV57, bits 63–57 must be equal to bit 56.
> >   */
> >  #ifdef CONFIG_64BIT
> > -#define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > +#define TASK_SIZE_64 (UL(1) << (VA_BITS - 1))
>
> Checked for l5, l4 and l3, and it seems a correct replacement.
>
> >
> >  #ifdef CONFIG_COMPAT
> > -#define TASK_SIZE_32 (_AC(0x80000000, UL))
> > -#define TASK_SIZE    (test_thread_flag(TIF_32BIT) ? \
> > +#define TASK_SIZE_32 (UL(1) << (VA_BITS_SV32 - 1))
>
> Oh, much better. Thanks for removing the magic number :)
>
> > +#define TASK_SIZE    (is_compat_task() ? \
> >                        TASK_SIZE_32 : TASK_SIZE_64)
I would remove is_compat_task() in the next version because your patch
contains that.

> >  #else
> >  #define TASK_SIZE    TASK_SIZE_64
> > --
> > 2.40.1
> >
>
> That's much more readable IMO now. Thanks!
>
> FWIW:
> Reviewed-by: Leonardo Bras <leobras@...hat.com>
>


-- 
Best Regards
 Guo Ren