On Wed, Jan 31, 2024 at 03:15:16AM +0800, Yangyu Chen wrote: > 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. > > > > 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 <[email protected]> > > --- > > arch/riscv/include/asm/processor.h | 22 +++++++++------------- > > 1 file changed, 9 insertions(+), 13 deletions(-) > > > > 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 @@ > > ({ \ > > unsigned long > > mmap_end; \ > > typeof(addr) _addr = (addr); \ > > - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && > > is_compat_task())) \ > > - mmap_end = STACK_TOP_MAX; \ > > - 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))) \ > > + mmap_end = STACK_TOP_MAX \ > > else \ > > - mmap_end = VA_USER_SV39; \ > > + mmap_end = (_addr + len); \ > > mmap_end; \ > > }) > > > > @@ -39,14 +37,12 @@ > > 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; \ > > Please mind that rnd_gap can be non-zero, in this case, the map will > fail. It will be better to let mmap_base = min((_addr + len), (base) + > TASK_SIZE - DEFAULT_MAP_WINDOW) .
Why would an rnd_gap that is non-zero cause mmap to fail? mmap will fail if rnd_gap is greater than (_addr + len). That is expected and should be interpreted as no address was available in the requested address space. mmap_base is used if the hint address is not available. I do see that I fumbled the test cases in this patch so I will fix that in a v3. - Charlie > > > mmap_base; \ > > }) > > > > >
