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http2: streamline OnStreamRead streamline memory accounting
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* avoid consecutive decrement/increment session memory calls.
* only Resize the buffer when it is needed.
* flip `stream_buf_offset_` condition to the LIKELY case.

PR-URL: #30351
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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lundibundi authored and targos committed Dec 9, 2019
1 parent 3840abe commit 71bb026
Showing 1 changed file with 11 additions and 9 deletions.
20 changes: 11 additions & 9 deletions src/node_http2.cc
Original file line number Diff line number Diff line change
Expand Up @@ -1862,7 +1862,11 @@ void Http2Session::OnStreamRead(ssize_t nread, const uv_buf_t& buf_) {

statistics_.data_received += nread;

if (UNLIKELY(stream_buf_offset_ > 0)) {
if (LIKELY(stream_buf_offset_ == 0)) {
// Shrink to the actual amount of used data.
buf.Resize(nread);
IncrementCurrentSessionMemory(nread);
} else {
// This is a very unlikely case, and should only happen if the ReadStart()
// call in OnStreamAfterWrite() immediately provides data. If that does
// happen, we concatenate the data we received with the already-stored
Expand All @@ -1871,20 +1875,18 @@ void Http2Session::OnStreamRead(ssize_t nread, const uv_buf_t& buf_) {
AllocatedBuffer new_buf = env()->AllocateManaged(pending_len + nread);
memcpy(new_buf.data(), stream_buf_.base + stream_buf_offset_, pending_len);
memcpy(new_buf.data() + pending_len, buf.data(), nread);

// The data in stream_buf_ is already accounted for, add nread received
// bytes to session memory but remove the already processed
// stream_buf_offset_ bytes.
IncrementCurrentSessionMemory(nread - stream_buf_offset_);

buf = std::move(new_buf);
nread = buf.size();
stream_buf_offset_ = 0;
stream_buf_ab_.Reset();

// We have now fully processed the stream_buf_ input chunk (by moving the
// remaining part into buf, which will be accounted for below).
DecrementCurrentSessionMemory(stream_buf_.len);
}

// Shrink to the actual amount of used data.
buf.Resize(nread);
IncrementCurrentSessionMemory(nread);

// Remember the current buffer, so that OnDataChunkReceived knows the
// offset of a DATA frame's data into the socket read buffer.
stream_buf_ = uv_buf_init(buf.data(), nread);
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