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| -rw-r--r-- | tools/profiler/docs/buffer.rst | 70 |
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diff --git a/tools/profiler/docs/buffer.rst b/tools/profiler/docs/buffer.rst new file mode 100644 index 0000000000..dd7ef30dfd --- /dev/null +++ b/tools/profiler/docs/buffer.rst @@ -0,0 +1,70 @@ +Buffers and Memory Management +============================= + +In a post-Fission world, precise memory management across many threads and processes is +especially important. In order for the profiler to achieve this, it uses a chunked buffer +strategy. + +The `ProfileBuffer`_ is the overall buffer class that controls the memory and storage +for the profile, it allows allocating objects into it. This can be used freely +by things like markers and samples to store data as entries, without needing to know +about the general strategy for how the memory is managed. + +The `ProfileBuffer`_ is then backed by the `ProfileChunkedBuffer`_. This specialized +buffer grows incrementally, by allocating additional `ProfileBufferChunk`_ objects. +More and more chunks will be allocated until a memory limit is reached, where they will +be released. After releasing, the chunk will either be recycled or freed. + +The limiting of memory usage is coordinated by the `ProfilerParent`_ in the parent +process. The `ProfilerParent`_ and `ProfilerChild`_ exchange IPC messages with information +about how much memory is being used. When the maximum byte threshold is passed, +the ProfileChunkManager in the parent process removes the oldest chunk, and then the +`ProfilerParent`_ sends a `DestroyReleasedChunksAtOrBefore`_ message to all of child +processes so that the oldest chunks in the profile are released. This helps long profiles +to keep having data in a similar time frame. + +Profile Buffer Terminology +########################## + +ProfilerParent + The main profiler machinery is installed in the parent process. It uses IPC to + communicate to the child processes. The PProfiler is the actor which is used + to communicate across processes to coordinate things. See `ProfilerParent.h`_. The + ProfilerParent uses the DestroyReleasedChunksAtOrBefore meessage to control the + overall chunk limit. + +ProfilerChild + ProfilerChild is installed in every child process, it will receive requests from + DestroyReleasedChunksAtOrBefore. + +Entry + This is an individual entry in the `ProfileBuffer.h`_,. These entry sizes are not + related to the chunks sizes. An individual entry can straddle two different chunks. + An entry can contain various pieces of data, like markers, samples, and stacks. + +Chunk + An arbitrary sized chunk of memory, managed by the `ProfileChunkedBuffer`_, and + IPC calls from the ProfilerParent. + +Unreleased Chunk + This chunk is currently being used to write entries into. + +Released chunk + This chunk is full of data. When memory limits happen, it can either be recycled + or freed. + +Recycled chunk + This is a chunk that was previously written into, and full. When memory limits occur, + rather than freeing the memory, it is re-used as the next chunk. + +.. _ProfileChunkedBuffer: https://searchfox.org/mozilla-central/search?q=ProfileChunkedBuffer&path=&case=true®exp=false +.. _ProfileChunkManager: https://searchfox.org/mozilla-central/search?q=ProfileBufferChunkManager.h&path=&case=true®exp=false +.. _ProfileBufferChunk: https://searchfox.org/mozilla-central/search?q=ProfileBufferChunk&path=&case=true®exp=false +.. _ProfileBufferChunkManagerWithLocalLimit: https://searchfox.org/mozilla-central/search?q=ProfileBufferChunkManagerWithLocalLimit&case=true&path= +.. _ProfilerParent.h: https://searchfox.org/mozilla-central/source/tools/profiler/public/ProfilerParent.h +.. _ProfilerChild.h: https://searchfox.org/mozilla-central/source/tools/profiler/public/ProfilerChild.h +.. _ProfileBuffer.h: https://searchfox.org/mozilla-central/source/tools/profiler/core/ProfileBuffer.h +.. _ProfileBuffer: https://searchfox.org/mozilla-central/search?q=ProfileBuffer&path=&case=true®exp=false +.. _ProfilerParent: https://searchfox.org/mozilla-central/search?q=ProfilerParent&path=&case=true®exp=false +.. _ProfilerChild: https://searchfox.org/mozilla-central/search?q=ProfilerChild&path=&case=true®exp=false +.. _DestroyReleasedChunksAtOrBefore: https://searchfox.org/mozilla-central/search?q=DestroyReleasedChunksAtOrBefore&path=&case=true®exp=false |