From e1813512c55d9464265e92f63f48593cb4055cff Mon Sep 17 00:00:00 2001 From: Adam Sawicki Date: Sat, 30 Oct 2021 23:29:01 +0200 Subject: [PATCH] Made virtual allocations not applying VMA_DEBUG_MARGIN Improved and regenerated documentation. --- docs/html/custom_memory_pools.html | 9 ++- docs/html/virtual_allocator.html | 4 +- include/vk_mem_alloc.h | 107 ++++++++++++++++++----------- 3 files changed, 72 insertions(+), 48 deletions(-) diff --git a/docs/html/custom_memory_pools.html b/docs/html/custom_memory_pools.html index c21f2e9..ff89d80 100644 --- a/docs/html/custom_memory_pools.html +++ b/docs/html/custom_memory_pools.html @@ -151,7 +151,7 @@ Linear allocation algorithm

Default allocation algorithm

Sometimes there is a need to use simpler, linear allocation algorithm. You can create custom pool that uses such algorithm by adding flag VMA_POOL_CREATE_LINEAR_ALGORITHM_BIT to VmaPoolCreateInfo::flags while creating VmaPool object. Then an alternative metadata management is used. It always creates new allocations after last one and doesn't reuse free regions after allocations freed in the middle. It results in better allocation performance and less memory consumed by metadata.

Linear allocation algorithm

-

With this one flag, you can create a custom pool that can be used in many ways: free-at-once, stack, double stack, and ring buffer. See below for details.

+

With this one flag, you can create a custom pool that can be used in many ways: free-at-once, stack, double stack, and ring buffer. See below for details. You don't need to specify explicitly which of these options you are going to use - it is detected automatically.

Free-at-once

In a pool that uses linear algorithm, you still need to free all the allocations individually, e.g. by using vmaFreeMemory() or vmaDestroyBuffer(). You can free them in any order. New allocations are always made after last one - free space in the middle is not reused. However, when you release all the allocation and the pool becomes empty, allocation starts from the beginning again. This way you can use linear algorithm to speed up creation of allocations that you are going to release all at once.

@@ -169,7 +169,7 @@ Double stack
  • First, default one, growing up from offset 0.
  • Second, "upper" one, growing down from the end towards lower offsets.
    • -

    To make allocation from upper stack, add flag VMA_ALLOCATION_CREATE_UPPER_ADDRESS_BIT to VmaAllocationCreateInfo::flags.

    +

    To make allocation from the upper stack, add flag VMA_ALLOCATION_CREATE_UPPER_ADDRESS_BIT to VmaAllocationCreateInfo::flags.

    Double stack

    Double stack is available only in pools with one memory block - VmaPoolCreateInfo::maxBlockCount must be 1. Otherwise behavior is undefined.

    When the two stacks' ends meet so there is not enough space between them for a new allocation, such allocation fails with usual VK_ERROR_OUT_OF_DEVICE_MEMORY error.

    @@ -182,10 +182,9 @@ Ring buffer

    Ring buffer is available only in pools with one memory block - VmaPoolCreateInfo::maxBlockCount must be 1. Otherwise behavior is undefined.

    Buddy allocation algorithm

    -

    There is another allocation algorithm that can be used with custom pools, called "buddy". Its internal data structure is based on a tree of blocks, each having size that is a power of two and a half of its parent's size. When you want to allocate memory of certain size, a free node in the tree is located. If it is too large, it is recursively split into two halves (called "buddies"). However, if requested allocation size is not a power of two, the size of a tree node is aligned up to the nearest power of two and the remaining space is wasted. When two buddy nodes become free, they are merged back into one larger node.

    +

    There is another allocation algorithm that can be used with custom pools, called "buddy". Its internal data structure is based on a binary tree of blocks, each having size that is a power of two and a half of its parent's size. When you want to allocate memory of certain size, a free node in the tree is located. If it is too large, it is recursively split into two halves (called "buddies"). However, if requested allocation size is not a power of two, the size of the allocation is aligned up to the nearest power of two and the remaining space is wasted. When two buddy nodes become free, they are merged back into one larger node.

    Buddy allocator

    -

    The advantage of buddy allocation algorithm over default algorithm is faster allocation and deallocation, as well as smaller external fragmentation. The disadvantage is more wasted space (internal fragmentation).

    -

    For more information, please search the Internet for "Buddy memory allocation" - sources that describe this concept in general.

    +

    The advantage of buddy allocation algorithm over default algorithm is faster allocation and deallocation, as well as smaller external fragmentation. The disadvantage is more wasted space (internal fragmentation). For more information, please search the Internet for "Buddy memory allocation" - sources that describe this concept in general.

    To use buddy allocation algorithm with a custom pool, add flag VMA_POOL_CREATE_BUDDY_ALGORITHM_BIT to VmaPoolCreateInfo::flags while creating VmaPool object.

    Several limitations apply to pools that use buddy algorithm: