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* [PATCH] ds: tmpio: avoid Perl target cache
@ 2021-10-06 11:50 Eric Wong
  0 siblings, 0 replies; only message in thread
From: Eric Wong @ 2021-10-06 11:50 UTC (permalink / raw)
  To: meta

The use of `substr' here an argument to `print' was causing Perl
to internally cache its target buffer.  Since `syswrite()'
already offers a buffer offset arg and length limits, just use
`syswrite' directly.  We were using autoflush anyways, so the
lack of buffering was of no concern performance-wise.

The target buffer could get to roughly ~10MB under some loads,
but it was usually a cold path and using memory which cannot be
released nor reused in other places.

note: IO::Handle::write uses `substr' internally, too;
so nothing would be gained using IO::Handle:write.
 lib/PublicInbox/ | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/ b/lib/PublicInbox/
index debb777a..9cca02d7 100644
--- a/lib/PublicInbox/
+++ b/lib/PublicInbox/
@@ -494,16 +494,15 @@ sub drop {
-# n.b.: use ->write/->read for this buffer to allow compatibility with
-# PerlIO::mmap or PerlIO::scalar if needed
 sub tmpio ($$$) {
 	my ($self, $bref, $off) = @_;
 	my $fh = tmpfile('wbuf', $self->{sock}, O_APPEND) or
 		return drop($self, "tmpfile $!");
 	my $len = length($$bref) - $off;
-	print $fh substr($$bref, $off, $len) or
+	my $n = syswrite($fh, $$bref, $len, $off) //
 		return drop($self, "write ($len): $!");
+	$n == $len or return drop($self, "wrote $n < $len bytes");
 	[ $fh, 0 ] # [1] = offset, [2] = length, not set by us

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2021-10-06 11:50 [PATCH] ds: tmpio: avoid Perl target cache Eric Wong

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