Make Large allocations naturally aligned #124
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This makes any large allocation naturally aligned to its size. This means all alignment requests can be handled without checks.
The PAL API previously allowed for returning more memory than asked for. This was when the PAL performed the alignment work, now this is done in large alloc, so removing from the PAL.
On platforms that do not support aligned mmap/VirtualAlloc, we need to produce heavily aligned blocks to guarantee we can meet all possible alignment requests. This commit grabs a block much larger than requested, and then produces "offcuts" before and after the block of smaller/same "large_classes". This enables one mmap/virtual alloc request to services many other requests for aligned memory.
By turning page access on and off, we can simulate the Windows Commit/Decommit states on Posix platforms. This is just enabled in Debug for now.
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#114 needs this. |
davidchisnall
approved these changes
Feb 5, 2020
davidchisnall
approved these changes
Feb 5, 2020
mjp41
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to mjp41/snmalloc-rs
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Feb 7, 2020
`snmalloc` now supports alignment of all allocations with microsoft/snmalloc#124 This comment is no longer required.
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This makes all large allocations aligned to their size next power of two size.
This introduces a new strategy for aligning blocks on platforms without a way to fetched aligned virtual memory (e.g. VirtualAlloc2, or mmap with MAP_ALIGNED).
To aid in debugging also uses mprotect to switch off unused pages in debug on posix platforms. This enables better testing of the Commit/Decommit code from Posix platforms.