91 lines
2.6 KiB
C++
91 lines
2.6 KiB
C++
#pragma once
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#if defined(__linux__)
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# include "../ds/bits.h"
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# include "pal_posix.h"
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# include <string.h>
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# include <sys/mman.h>
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extern "C" int puts(const char* str);
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namespace snmalloc
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{
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class PALLinux : public PALPOSIX<PALLinux>
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{
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public:
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/**
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* Bitmap of PalFeatures flags indicating the optional features that this
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* PAL supports.
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*
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* Linux does not support any features other than those in a generic POSIX
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* platform. This field is declared explicitly to remind anyone who
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* extends this PAL that they may need to extend the set of advertised
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* features.
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*/
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static constexpr uint64_t pal_features = PALPOSIX::pal_features;
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static constexpr size_t page_size =
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Aal::aal_name == PowerPC ? 0x10000 : PALPOSIX::page_size;
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/**
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* Linux requires an explicit no-reserve flag in `mmap` to guarantee lazy
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* commit if /proc/sys/vm/overcommit_memory is set to `heuristic` (0).
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*
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* https://www.kernel.org/doc/html/latest/vm/overcommit-accounting.html
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*/
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static constexpr int default_mmap_flags = MAP_NORESERVE;
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/**
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* OS specific function for zeroing memory.
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*
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* Linux implements an unusual interpretation of `MADV_DONTNEED`, which
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* immediately resets the pages to the zero state (rather than marking them
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* as sensible ones to swap out in high memory pressure). We use this to
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* clear the underlying memory range.
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*/
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template<bool page_aligned = false>
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static void zero(void* p, size_t size) noexcept
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{
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// QEMU does not seem to be giving the desired behaviour for
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// MADV_DONTNEED. switch back to memset only for QEMU.
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# ifndef SNMALLOC_QEMU_WORKAROUND
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if (
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(page_aligned || is_aligned_block<page_size>(p, size)) &&
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(size > 16 * page_size))
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{
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// Only use this on large allocations as memset faster, and doesn't
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// introduce IPI so faster for small allocations.
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SNMALLOC_ASSERT(is_aligned_block<page_size>(p, size));
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madvise(p, size, MADV_DONTNEED);
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}
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else
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# endif
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{
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::memset(p, 0, size);
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}
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}
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static void notify_not_using(void* p, size_t size) noexcept
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{
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SNMALLOC_ASSERT(is_aligned_block<page_size>(p, size));
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if constexpr (PalEnforceAccess)
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{
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# if !defined(NDEBUG)
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// Fill memory so that when we switch the pages back on we don't make
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// assumptions on the content.
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memset(p, 0x5a, size);
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# endif
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madvise(p, size, MADV_FREE);
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mprotect(p, size, PROT_NONE);
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}
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else
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{
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madvise(p, size, MADV_FREE);
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}
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}
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};
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} // namespace snmalloc
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#endif
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