Received-SPF: pass (google.com: domain of linux-kernel+bounces-45175-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <tencent_34680F3AAAE356C4A485103556F3F909C60A@qq.com>
Subject: Re: [PATCH v2 1/3] riscv: mm: Use hint address in mmap if available
From: Yangyu Chen <cyy@cyyself.name>
To: Charlie Jenkins <charlie@rivosinc.com>, 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>
Cc: linux-mm@kvack.org, linux-riscv@lists.infradead.org, 
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, 
	linux-doc@vger.kernel.org
Date: Wed, 31 Jan 2024 03:15:16 +0800
In-Reply-To: <20240130-use_mmap_hint_address-v2-1-f34ebfd33053@rivosinc.com>
References: <20240130-use_mmap_hint_address-v2-0-f34ebfd33053@rivosinc.com>
	 <20240130-use_mmap_hint_address-v2-1-f34ebfd33053@rivosinc.com>
Autocrypt: addr=cyy@cyyself.name; prefer-encrypt=mutual;
 keydata=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
	0mslfht1JyMf5dUi38RQI/fOO0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.50.3-1 
Precedence: bulk
MIME-Version: 1.0

On Tue, 2024-01-30 at 11:04 -0800, 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.
>=20
> 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.
>=20
> 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.
>=20
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
> =C2=A0arch/riscv/include/asm/processor.h | 22 +++++++++-------------
> =C2=A01 file changed, 9 insertions(+), 13 deletions(-)
>=20
> diff --git a/arch/riscv/include/asm/processor.h
> b/arch/riscv/include/asm/processor.h
> index f19f861cda54..5d966ae81a58 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -22,14 +22,12 @@
> =C2=A0({								\
> =C2=A0	unsigned long
> mmap_end;					\
> =C2=A0	typeof(addr) _addr =3D (addr);				\
> -	if ((_addr) =3D=3D 0 || (IS_ENABLED(CONFIG_COMPAT) &&
> is_compat_task())) \
> -		mmap_end =3D STACK_TOP_MAX;			\
> -	else if ((_addr) >=3D VA_USER_SV57)			\
> -		mmap_end =3D STACK_TOP_MAX;			\
> -	else if ((((_addr) >=3D VA_USER_SV48)) && (VA_BITS >=3D
> VA_BITS_SV48)) \
> -		mmap_end =3D VA_USER_SV48;			\
> +	if ((_addr) =3D=3D 0 ||					\
> +	=C2=A0=C2=A0=C2=A0 (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) ||	\
> +	=C2=A0=C2=A0=C2=A0 ((_addr + len) > BIT(VA_BITS -
> 1)))			\
> +		mmap_end =3D STACK_TOP_MAX			\
> =C2=A0	else							\
> -		mmap_end =3D VA_USER_SV39;			\
> +		mmap_end =3D (_addr + len);			\
> =C2=A0	mmap_end;						\
> =C2=A0})
> =C2=A0
> @@ -39,14 +37,12 @@
> =C2=A0	typeof(addr) _addr =3D (addr);				\
> =C2=A0	typeof(base) _base =3D (base);				\
> =C2=A0	unsigned long rnd_gap =3D DEFAULT_MAP_WINDOW - (_base);	\
> -	if ((_addr) =3D=3D 0 || (IS_ENABLED(CONFIG_COMPAT) &&
> is_compat_task())) \
> +	if ((_addr) =3D=3D 0 ||					\
> +	=C2=A0=C2=A0=C2=A0 (IS_ENABLED(CONFIG_COMPAT) && is_compat_task()) ||	\
> +	=C2=A0=C2=A0=C2=A0 ((_addr + len) > BIT(VA_BITS -
> 1)))			\
> =C2=A0		mmap_base =3D (_base);				\
> -	else if (((_addr) >=3D VA_USER_SV57) && (VA_BITS >=3D
> VA_BITS_SV57)) \
> -		mmap_base =3D VA_USER_SV57 - rnd_gap;		\
> -	else if ((((_addr) >=3D VA_USER_SV48)) && (VA_BITS >=3D
> VA_BITS_SV48)) \
> -		mmap_base =3D VA_USER_SV48 - rnd_gap;		\
> =C2=A0	else							\
> -		mmap_base =3D VA_USER_SV39 - rnd_gap;		\
> +		mmap_base =3D (_addr + len) - rnd_gap;		\

Please mind that rnd_gap can be non-zero, in this case, the map will
fail. It will be better to let mmap_base =3D min((_addr + len), (base) +
TASK_SIZE - DEFAULT_MAP_WINDOW) .

> =C2=A0	mmap_base;						\
> =C2=A0})
> =C2=A0
>=20