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Code Issues Releases Wiki Activity

Limit memory usage of ssh-exec during large pull operations

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Summary: Fixes T4241. Ref T4206. See T4241 for a description here. Generally, when we connect a fat pipe (`git-upload-pack`) to a narrow one (`git` over SSH) we currently read limitless data into memory. Instead, throttle reads until writes catch up. This is now possible because of the previous changes in this sequence.

Test Plan:
  - Ran `git clone` and `git push` on the entire Wine repository.
  - Observed CPU and memory usage.
  - Memory usage was constant and low, CPU usage was high only during I/O (which is expected, since we have to actually do work, although thre might be room to further reduce this).

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4241, T4206

Differential Revision: https://secure.phabricator.com/D7776
This commit is contained in:
epriestley 2013-12-16 12:37:32 -08:00
parent 537f2eabee
commit f7464400a5
1 changed files with 45 additions and 3 deletions
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48
src/infrastructure/ssh/PhabricatorSSHPassthruCommand.php
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@ -97,6 +97,18 @@ final class PhabricatorSSHPassthruCommand extends Phobject {
$channels = array($command_channel, $io_channel, $error_channel);
// We want to limit the amount of data we'll hold in memory for this
// process. See T4241 for a discussion of this issue in general.
$buffer_size = (1024 * 1024); // 1MB
$io_channel->setReadBufferSize($buffer_size);
$command_channel->setReadBufferSize($buffer_size);
// TODO: This just makes us throw away stderr after the first 1MB, but we
// don't currently have the support infrastructure to buffer it correctly.
// It's difficult to imagine this causing problems in practice, though.
$this->execFuture->getStderrSizeLimit($buffer_size);
while (true) {
PhutilChannel::waitForAny($channels);
@ -104,7 +116,29 @@ final class PhabricatorSSHPassthruCommand extends Phobject {
$command_channel->update();
$error_channel->update();
$done = !$command_channel->isOpen();
// If any channel is blocked on the other end, wait for it to flush before
// we continue reading. For example, if a user is running `git clone` on
// a 1GB repository, the underlying `git-upload-pack` may
// be able to produce data much more quickly than we can send it over
// the network. If we don't throttle the reads, we may only send a few
// MB over the I/O channel in the time it takes to read the entire 1GB off
// the command channel. That leaves us with 1GB of data in memory.
while ($command_channel->isOpen() &&
$io_channel->isOpenForWriting() &&
($command_channel->getWriteBufferSize() >= $buffer_size ||
$io_channel->getWriteBufferSize() >= $buffer_size ||
$error_channel->getWriteBufferSize() >= $buffer_size)) {
PhutilChannel::waitForActivity(array(), $channels);
$io_channel->update();
$command_channel->update();
$error_channel->update();
}
// If the subprocess has exited and we've read everything from it,
// we're all done.
$done = !$command_channel->isOpenForReading() &&
$command_channel->isReadBufferEmpty();
$in_message = $io_channel->read();
if ($in_message !== null) {
@ -133,12 +167,20 @@ final class PhabricatorSSHPassthruCommand extends Phobject {
// If the client has disconnected, kill the subprocess and bail.
if (!$io_channel->isOpenForWriting()) {
$this->execFuture->resolveKill();
$this->execFuture
->setStdoutSizeLimit(0)
->setStderrSizeLimit(0)
->setReadBufferSize(null)
->resolveKill();
break;
}
}
list($err) = $this->execFuture->resolve();
list($err) = $this->execFuture
->setStdoutSizeLimit(0)
->setStderrSizeLimit(0)
->setReadBufferSize(null)
->resolve();
return $err;
}