On Wed, Nov 08, 2017 at 03:56:06PM +1100, Michael Ellerman wrote: > "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes: > > >> > >> If it is decided to keep these kind of heuristics, can we get just a > >> small but reasonably precise description of each change to the > >> interface and ways for using the new functionality, such that would be > >> suitable for the man page? I couldn't fix powerpc because nothing > >> matches and even Aneesh and you differ on some details (MAP_FIXED > >> behaviour). > > > > > > I would consider MAP_FIXED as my mistake. We never discussed this > > explicitly and I kind of assumed it to behave the same way. ie, we > > search in lower address space (128TB) if the hint addr is below 128TB. > > > > IIUC we agree on the below. > > > > 1) MAP_FIXED allow the addr to be used, even if hint addr is below 128TB > > but hint_addr + len is > 128TB. > > So: > mmap(0x7ffffffff000, 0x2000, ..., MAP_FIXED ...) = 0x7ffffffff000 > > > 2) For everything else we search in < 128TB space if hint addr is below > > 128TB > > mmap((x < 128T), 0x1000, ...) = (y < 128T) > ... > mmap(0x7ffffffff000, 0x1000, ...) = 0x7ffffffff000 > mmap(0x800000000000, 0x1000, ...) = 0x800000000000 > ... > mmap((x >= 128T), 0x1000, ...) = (y >= 128T) > > > 3) We don't switch to large address space if hint_addr + len > 128TB. > > The decision to switch to large address space is primarily based on hint > > addr > > But does the mmap succeed in that case or not? > > ie: mmap(0x7ffffffff000, 0x2000, ...) = ? It does, but resulting address doesn't match the hint. It's somewhere below 47-bit border. -- Kirill A. Shutemov
