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From:   Atish Patra <atishp@atishpatra.org>
Date:   Mon, 14 Sep 2020 10:53:00 -0700
Message-ID: <CAOnJCUKqUZVTKzgjK0=Kj_WCZU+hP27SX8V0mvT+2AVk_MMC5w@mail.gmail.com>
Subject: Re: [PATCH] RISC-V: Consider sparse memory while removing unusable memory
To:     Anup Patel <anup@brainfault.org>
Cc:     Mike Rapoport <rppt@kernel.org>, Anup Patel <anup.patel@wdc.com>,
        Atish Patra <atish.patra@wdc.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Zong Li <zong.li@sifive.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv <linux-riscv@lists.infradead.org>
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On Mon, Sep 14, 2020 at 4:52 AM Anup Patel <anup@brainfault.org> wrote:
>
> On Mon, Sep 14, 2020 at 5:18 AM Atish Patra <atishp@atishpatra.org> wrote:
> >
> > On Sat, Sep 12, 2020 at 3:45 AM Mike Rapoport <rppt@kernel.org> wrote:
> > >
> > > Hello Atish,
> > >
> > > On Fri, Sep 11, 2020 at 05:23:41PM -0700, Atish Patra wrote:
> > > > Currently, any usable memory area beyond page_offset is removed by adding the
> > > > memory sizes from each memblock. That may not work for sparse memory
> > > > as memory regions can be very far apart resulting incorrect removal of some
> > > > usable memory.
> > >
> > > If I understand correctly, the memory with physical addresses larger
> > > than (-PAGE_OFFSET) cannot be used. Since it was aready
> > > memblock_add()'ed during device tree parsing, you need to remove it from
> > > memblock.
> > >
> >
> > IIRC, the original intention was to fix MAXPHYSMEM_2GB option for RV64
> > for the medlow model.
> > That's why the patch removed any memory beyond -PAGE_OFFSET.
> >
> > > For that you can use memblock_enforce_memory_limit(-PAGE_OFFSET).
> > >
> > Thanks. I think we can just call memblock_enforce_memory_limit without
> > tracking the total memory size
> > and whether maximum memory described in DT is greater than  -PAGE_OFFSET.
> >
> > @Anup Patel Was there any other reason for this change originally?
>
> No other reason. We just wanted to ensure that amount of memory addressable
> by kernel (i.e. -PAGE_OFFSET) is also considered when removing memblock.
>

It looks like we have an agreement here then. I will update the patch
to directly call
memblock_enforce_memory_limit as suggested by Mike.

> Regards,
> Anup
>
> >
> > > > Just use the start of the first memory block and the end of the last memory
> > > > block to compute the size of the total memory that can be used.
> > > >
> > > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > > > ---
> > > >  arch/riscv/mm/init.c | 6 ++----
> > > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > > > index 787c75f751a5..188281fc2816 100644
> > > > --- a/arch/riscv/mm/init.c
> > > > +++ b/arch/riscv/mm/init.c
> > > > @@ -147,7 +147,6 @@ void __init setup_bootmem(void)
> > > >  {
> > > >       struct memblock_region *reg;
> > > >       phys_addr_t mem_size = 0;
> > > > -     phys_addr_t total_mem = 0;
> > > >       phys_addr_t mem_start, end = 0;
> > > >       phys_addr_t vmlinux_end = __pa_symbol(&_end);
> > > >       phys_addr_t vmlinux_start = __pa_symbol(&_start);
> > > > @@ -155,18 +154,17 @@ void __init setup_bootmem(void)
> > > >       /* Find the memory region containing the kernel */
> > > >       for_each_memblock(memory, reg) {
> > > >               end = reg->base + reg->size;
> > > > -             if (!total_mem)
> > > > +             if (!mem_start)
> > > >                       mem_start = reg->base;
> > > >               if (reg->base <= vmlinux_start && vmlinux_end <= end)
> > > >                       BUG_ON(reg->size == 0);
> > > > -             total_mem = total_mem + reg->size;
> > > >       }
> > > >
> > > >       /*
> > > >        * Remove memblock from the end of usable area to the
> > > >        * end of region
> > > >        */
> > > > -     mem_size = min(total_mem, (phys_addr_t)-PAGE_OFFSET);
> > > > +     mem_size = min(end - mem_start, (phys_addr_t)-PAGE_OFFSET);
> > > >       if (mem_start + mem_size < end)
> > > >               memblock_remove(mem_start + mem_size,
> > > >                               end - mem_start - mem_size);
> > > > --
> > > > 2.24.0
> > > >
> > >
> > > --
> > > Sincerely yours,
> > > Mike.
> > >
> > > _______________________________________________
> > > linux-riscv mailing list
> > > linux-riscv@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
> >
> >
> > --
> > Regards,
> > Atish


-- 
Regards,
Atish