From: Charlie Jenkins <charlie@rivosinc.com>
To: Stefan O'Rear <sorear@fastmail.com>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>, Shuah Khan <shuah@kernel.org>,
Jonathan Corbet <corbet@lwn.net>, Yangyu Chen <cyy@cyyself.name>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH 1/3] riscv: mm: Use hint address in mmap if available
Date: Mon, 29 Jan 2024 18:04:29 -0800 [thread overview]
Message-ID: <ZbhZLewEscaayuaG@ghost> (raw)
In-Reply-To: <46b90dbc-3b5f-4f52-8539-0f6fa7e28ce9@app.fastmail.com>
On Mon, Jan 29, 2024 at 08:53:31PM -0500, Stefan O'Rear wrote:
> On Mon, Jan 29, 2024, at 7:37 PM, Charlie Jenkins wrote:
> > On riscv it is guaranteed that the address returned by mmap is less than
> > the hint address. Allow mmap to return an address all the way up to
> > addr, if provided, rather than just up to the lower address space.
> >
> > This provides a performance benefit as well, allowing mmap to exit after
> > checking that the address is in range rather than searching for a valid
> > address.
> >
> > It is possible to provide an address that uses at most the same number
> > of bits, however it is significantly more computationally expensive to
> > provide that number rather than setting the max to be the hint address.
> > There is the instruction clz/clzw in Zbb that returns the highest set bit
> > which could be used to performantly implement this, but it would still
> > be slower than the current implementation. At worst case, half of the
> > address would not be able to be allocated when a hint address is
> > provided.
> >
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> > arch/riscv/include/asm/processor.h | 21 ++++++++-------------
> > 1 file changed, 8 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/processor.h
> > b/arch/riscv/include/asm/processor.h
> > index f19f861cda54..f3ea5166e3b2 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -22,14 +22,11 @@
> > ({ \
> > unsigned long mmap_end; \
> > typeof(addr) _addr = (addr); \
> > - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> > - mmap_end = STACK_TOP_MAX; \
>
> Setting mmap_end in the no-hint case seems to have been lost?
>
> -s
Thanks for catching that, will fix in v2.
- Charlie
>
> > - else if ((_addr) >= VA_USER_SV57) \
> > - mmap_end = STACK_TOP_MAX; \
> > - else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
> > - mmap_end = VA_USER_SV48; \
> > + if ((_addr) == 0 || \
> > + (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
> > + ((_addr + len) > BIT(VA_BITS - 1))) \
> > else \
> > - mmap_end = VA_USER_SV39; \
> > + mmap_end = (_addr + len); \
> > mmap_end; \
> > })
> >
> > @@ -39,14 +36,12 @@
> > typeof(addr) _addr = (addr); \
> > typeof(base) _base = (base); \
> > unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base); \
> > - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> > + if ((_addr) == 0 || \
> > + (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) || \
> > + ((_addr + len) > BIT(VA_BITS - 1))) \
> > mmap_base = (_base); \
> > - else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
> > - mmap_base = VA_USER_SV57 - rnd_gap; \
> > - else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
> > - mmap_base = VA_USER_SV48 - rnd_gap; \
> > else \
> > - mmap_base = VA_USER_SV39 - rnd_gap; \
> > + mmap_base = (_addr + len) - rnd_gap; \
> > mmap_base; \
> > })
> >
> >
> > --
> > 2.43.0
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2024-01-30 2:04 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-30 0:36 [PATCH 0/3] riscv: mm: Use hint address in mmap if available Charlie Jenkins
2024-01-30 0:37 ` [PATCH 1/3] " Charlie Jenkins
2024-01-30 1:53 ` Stefan O'Rear
2024-01-30 2:04 ` Charlie Jenkins [this message]
2024-01-30 2:34 ` Yangyu Chen
2024-01-30 2:50 ` Charlie Jenkins
2024-01-30 7:42 ` Yangyu Chen
2024-01-30 21:05 ` kernel test robot
2024-01-30 22:12 ` kernel test robot
2024-01-30 0:37 ` [PATCH 2/3] selftests: riscv: Generalize mm selftests Charlie Jenkins
2024-01-30 0:37 ` [PATCH 3/3] docs: riscv: Define behavior of mmap Charlie Jenkins
2024-01-30 2:04 ` [PATCH 0/3] riscv: mm: Use hint address in mmap if available Stefan O'Rear
2024-01-30 2:13 ` Charlie Jenkins
2024-01-30 22:04 ` Stefan O'Rear
2024-01-30 22:10 ` Charlie Jenkins
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