[llvm-commits] [llvm] r151834 - in /llvm/trunk: lib/Support/Allocator.cpp unittests/Support/AllocatorTest.cpp

[Benjamin Kramer]

On 01.03.2012, at 21:36, Argyrios Kyrtzidis wrote:

> Author: akirtzidis
> Date: Thu Mar  1 14:36:32 2012
> New Revision: 151834
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=151834&view=rev
> Log:
> If BumpPtrAllocator is requested to allocate a size that exceeds the slab size,
> increase the slab size.
> 
> Modified:
>    llvm/trunk/lib/Support/Allocator.cpp
>    llvm/trunk/unittests/Support/AllocatorTest.cpp
> 
> Modified: llvm/trunk/lib/Support/Allocator.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Allocator.cpp?rev=151834&r1=151833&r2=151834&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/Allocator.cpp (original)
> +++ llvm/trunk/lib/Support/Allocator.cpp Thu Mar  1 14:36:32 2012
> @@ -87,15 +87,21 @@
> /// Allocate - Allocate space at the specified alignment.
> ///
> void *BumpPtrAllocator::Allocate(size_t Size, size_t Alignment) {
> +  // 0-byte alignment means 1-byte alignment.
> +  if (Alignment == 0) Alignment = 1;
> +
> +  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
> +
> +  // If requested size exceeds slab size, increase slab size.
> +  while (PaddedSize > SlabSize)
> +    SlabSize *= 2;

Have you measured that this doesn't make us waste a ton of memory? Also this makes the "separate slab" code below redundant.

BumpPtrAllocator already (slowly) grows the allocation size when a lot of stuff is allocated, see StartNewSlab. Back then I tweaked the parameters there to minimize wasted memory in clang's ASTContext. If you're seeing a lot of malloc calls it may make sense to revisit the parameters there or initialize an allocator with a bigger slab size.

- Ben

> +
>   if (!CurSlab) // Start a new slab if we haven't allocated one already.
>     StartNewSlab();
> 
>   // Keep track of how many bytes we've allocated.
>   BytesAllocated += Size;
> 
> -  // 0-byte alignment means 1-byte alignment.
> -  if (Alignment == 0) Alignment = 1;
> -
>   // Allocate the aligned space, going forwards from CurPtr.
>   char *Ptr = AlignPtr(CurPtr, Alignment);
> 
> @@ -106,7 +112,6 @@
>   }
> 
>   // If Size is really big, allocate a separate slab for it.
> -  size_t PaddedSize = Size + sizeof(MemSlab) + Alignment - 1;
>   if (PaddedSize > SizeThreshold) {
>     MemSlab *NewSlab = Allocator.Allocate(PaddedSize);
> 
> 
> Modified: llvm/trunk/unittests/Support/AllocatorTest.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/AllocatorTest.cpp?rev=151834&r1=151833&r2=151834&view=diff
> ==============================================================================
> --- llvm/trunk/unittests/Support/AllocatorTest.cpp (original)
> +++ llvm/trunk/unittests/Support/AllocatorTest.cpp Thu Mar  1 14:36:32 2012
> @@ -93,6 +93,14 @@
>   EXPECT_EQ(2U, Alloc.GetNumSlabs());
> }
> 
> +// Test allocating with a size larger than the initial slab size.
> +TEST(AllocatorTest, TestSmallSlabSize) {
> +  BumpPtrAllocator Alloc(128);
> +
> +  Alloc.Allocate(200, 0);
> +  EXPECT_EQ(1U, Alloc.GetNumSlabs());
> +}
> +
> // Mock slab allocator that returns slabs aligned on 4096 bytes.  There is no
> // easy portable way to do this, so this is kind of a hack.
> class MockSlabAllocator : public SlabAllocator {
> 
> 
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