From 7c8fc8142e990b862333ea62d446618f249f70e3 Mon Sep 17 00:00:00 2001 From: Rui Ueyama Date: Wed, 23 Jan 2019 02:03:26 +0000 Subject: MemoryBlock: Do not automatically extend a given size to a multiple of page size. Previously, MemoryBlock automatically extends a requested buffer size to a multiple of page size because (I believe) doing it was thought to be harmless and with that you could get more memory (on average 2KiB on 4KiB-page systems) "for free". That programming interface turned out to be error-prone. If you request N bytes, you usually expect that a resulting object returns N for `size()`. That's not the case for MemoryBlock. Looks like there is only one place where we take the advantage of allocating more memory than the requested size. So, with this patch, I simply removed the automatic size expansion feature from MemoryBlock and do it on the caller side when needed. MemoryBlock now always returns a buffer whose size is equal to the requested size. Differential Revision: https://reviews.llvm.org/D56941 llvm-svn: 351916 --- llvm/lib/Support/Unix/Memory.inc | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'llvm/lib/Support/Unix/Memory.inc') diff --git a/llvm/lib/Support/Unix/Memory.inc b/llvm/lib/Support/Unix/Memory.inc index c20629c8217..3c4d324a8bb 100644 --- a/llvm/lib/Support/Unix/Memory.inc +++ b/llvm/lib/Support/Unix/Memory.inc @@ -91,9 +91,6 @@ Memory::allocateMappedMemory(size_t NumBytes, if (NumBytes == 0) return MemoryBlock(); - static const size_t PageSize = Process::getPageSize(); - const size_t NumPages = (NumBytes+PageSize-1)/PageSize; - int fd = -1; int MMFlags = MAP_PRIVATE | @@ -113,11 +110,12 @@ Memory::allocateMappedMemory(size_t NumBytes, // Use any near hint and the page size to set a page-aligned starting address uintptr_t Start = NearBlock ? reinterpret_cast(NearBlock->base()) + NearBlock->size() : 0; + static const size_t PageSize = Process::getPageSize(); if (Start && Start % PageSize) Start += PageSize - Start % PageSize; - void *Addr = ::mmap(reinterpret_cast(Start), PageSize*NumPages, - Protect, MMFlags, fd, 0); + void *Addr = ::mmap(reinterpret_cast(Start), NumBytes, Protect, + MMFlags, fd, 0); if (Addr == MAP_FAILED) { if (NearBlock) //Try again without a near hint return allocateMappedMemory(NumBytes, nullptr, PFlags, EC); @@ -128,7 +126,7 @@ Memory::allocateMappedMemory(size_t NumBytes, MemoryBlock Result; Result.Address = Addr; - Result.Size = NumPages*PageSize; + Result.Size = NumBytes; // Rely on protectMappedMemory to invalidate instruction cache. if (PFlags & MF_EXEC) { -- cgit v1.2.3