[PATCH] gcf2 + extsearch: check for unlinked files on Linux

[Eric Wong <e@80x24.org>]

Eric Wong <e@80x24.org> wrote:
> Konstantin Ryabitsev <konstantin@linuxfoundation.org> wrote:
> > Well, it may also not be something that's the responsibility of public-inbox
> > either, e.g. other long-running daemons don't perform such checks. We can just
> > issue a reload after we've done repacking.
> 
> The less operational knowledge required, the better; especially
> since I'd like to see more self-hosted instances pop up.

I've lightly tested the patch below; but I'm questioning the
need for Gcf2 if /all/ is configured (more on that later, need nap)

-----------8<---------
Subject: [PATCH] gcf2 + extsearch: check for unlinked files on Linux

Check for unlinked mmap-ed files via /proc/$PID/maps every 60s
or so.

ExtSearch (extindex) is compatible-enough with Inbox objects to
be wired into the old per-inbox code, but the startup cost is
projected to be much higher down the line when there's >30K
inboxes, so we scan /proc/$PID/maps for deleted files before
unlinking.  With old Inbox objects, it was (and is) simpler to
just kill processes w/o checking due to the low startup cost
(and non-portability of checking).

Reported-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Link: https://public-inbox.org/meta/20210921144754.gulkneuulzo27qbw@meerkat.local/
---
 lib/PublicInbox/ExtSearch.pm | 10 ++++++++--
 lib/PublicInbox/Gcf2.pm      | 26 +++++++++++++++++++++++---
 lib/PublicInbox/Git.pm       | 16 +++++++++++++++-
 lib/PublicInbox/Inbox.pm     | 11 +++++++++--
 4 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/lib/PublicInbox/ExtSearch.pm b/lib/PublicInbox/ExtSearch.pm
index bd301158..cd7cba2e 100644
--- a/lib/PublicInbox/ExtSearch.pm
+++ b/lib/PublicInbox/ExtSearch.pm
@@ -33,12 +33,18 @@ sub misc {
 # same as per-inbox ->over, for now...
 sub over {
 	my ($self) = @_;
-	$self->{over} //= PublicInbox::Over->new("$self->{xpfx}/over.sqlite3");
+	$self->{over} //= do {
+		PublicInbox::Inbox::_cleanup_later($self);
+		PublicInbox::Over->new("$self->{xpfx}/over.sqlite3");
+	};
 }
 
 sub git {
 	my ($self) = @_;
-	$self->{git} //= PublicInbox::Git->new("$self->{topdir}/ALL.git");
+	$self->{git} //= do {
+		PublicInbox::Inbox::_cleanup_later($self);
+		PublicInbox::Git->new("$self->{topdir}/ALL.git");
+	};
 }
 
 # returns a hashref of { $NEWSGROUP_NAME => $ART_NO } using the `xref3' table
diff --git a/lib/PublicInbox/Gcf2.pm b/lib/PublicInbox/Gcf2.pm
index 64945ca6..f546208f 100644
--- a/lib/PublicInbox/Gcf2.pm
+++ b/lib/PublicInbox/Gcf2.pm
@@ -8,6 +8,7 @@ use strict;
 use v5.10.1;
 use PublicInbox::Spawn qw(which popen_rd); # may set PERL_INLINE_DIRECTORY
 use Fcntl qw(LOCK_EX SEEK_SET);
+use Time::HiRes qw(clock_gettime CLOCK_MONOTONIC);
 use IO::Handle; # autoflush
 BEGIN {
 	my (%CFG, $c_src);
@@ -96,11 +97,21 @@ sub add_alt ($$) {
 	1;
 }
 
-# Usage: $^X -MPublicInbox::Gcf2 -e PublicInbox::Gcf2::loop
+sub have_unlinked_files () {
+	# FIXME: port gcf2-like over to git.git so we won't need to
+	# deal with libgit2
+	return 1 if $^O ne 'linux';
+	open my $fh, '<', "/proc/$$/maps" or return;
+	while (<$fh>) { return 1 if /\.(?:idx|pack) \(deleted\)$/ }
+	undef;
+}
+
+# Usage: $^X -MPublicInbox::Gcf2 -e PublicInbox::Gcf2::loop [EXPIRE-TIMEOUT]
 # (see lib/PublicInbox/Gcf2Client.pm)
-sub loop () {
+sub loop (;$) {
+	my $exp = $_[0] || $ARGV[0] || 60; # seconds
 	my $gcf2 = new();
-	my %seen;
+	my (%seen, $check_at);
 	STDERR->autoflush(1);
 	STDOUT->autoflush(1);
 
@@ -116,6 +127,7 @@ sub loop () {
 
 			$gcf2 = new();
 			%seen = ($git_dir => add_alt($gcf2,"$git_dir/objects"));
+			$check_at = clock_gettime(CLOCK_MONOTONIC) + $exp;
 
 			if ($gcf2->cat_oid(1, $oid)) {
 				warn "I: $$ $oid found after retry\n";
@@ -123,6 +135,14 @@ sub loop () {
 				warn "W: $$ $oid missing after retry\n";
 				print "$oid missing\n"; # mimic git-cat-file
 			}
+		} else { # check expiry to deal with deleted pack files
+			my $now = clock_gettime(CLOCK_MONOTONIC);
+			$check_at //= $now + $exp;
+			if ($now > $check_at && have_unlinked_files()) {
+				undef $check_at;
+				$gcf2 = new();
+				%seen = ();
+			}
 		}
 	}
 }
diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index 5ef1db2f..cf51239f 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -12,7 +12,7 @@ use v5.10.1;
 use parent qw(Exporter);
 use POSIX ();
 use IO::Handle; # ->autoflush
-use Errno qw(EINTR EAGAIN);
+use Errno qw(EINTR EAGAIN ENOENT);
 use File::Glob qw(bsd_glob GLOB_NOSORT);
 use File::Spec ();
 use Time::HiRes qw(stat);
@@ -523,6 +523,20 @@ sub manifest_entry {
 	$ent;
 }
 
+sub cleanup_if_unlinked {
+	my ($self) = @_;
+	return cleanup($self) if $^O ne 'linux';
+	# Linux-specific /proc/$PID/maps access
+	# TODO: support this inside git.git
+	for my $fld (qw(pid pid_c)) {
+		my $pid = $self->{$fld} // next;
+		open my $fh, '<', "/proc/$pid/maps" or next;
+		while (<$fh>) {
+			return cleanup($self) if /\.(?:idx|pack) \(deleted\)$/;
+		}
+	}
+}
+
 1;
 __END__
 =pod
diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index 20f8c884..02ffc7be 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -22,8 +22,15 @@ my $CLEANUP = {}; # string(inbox) -> inbox
 
 sub git_cleanup ($) {
 	my ($self) = @_;
-	my $git = $self->{git} or return;
-	$git->cleanup;
+	if ($self->isa(__PACKAGE__)) {
+		# normal Inbox; low startup cost, and likely to have many
+		# many so this keeps process/pipe counts in check
+		$self->{git}->cleanup if $self->{git};
+	} else {
+		# ExtSearch, high startup cost if ->ALL, and probably
+		# only one per-daemon, so teardown only if required:
+		$self->git->cleanup_if_unlinked;
+	}
 }
 
 sub cleanup_task () {