From ac0ad2064763dc0881dd028d3ee04a0169dd6293 Mon Sep 17 00:00:00 2001
From: Wolfgang Draxinger <Wolfgang.Draxinger@draxit.de>
Date: Mon, 6 Apr 2015 01:50:01 +0200
Subject: resource limits checking and diagnostic messages

---
 README   |  6 +++++-
 fmlock.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/README b/README
index cad20e8..f93fa50 100644
--- a/README
+++ b/README
@@ -4,13 +4,17 @@ fmlock is a small tool intended to load file into the block I/O cache and lock
 them there. This is done by mmap-ing the whole file and calling mlock on the
 address space occupied by the file. In addition the whole file is read to heat
 the cache; this should not be necessary, but some systems may require this, for
-this tool to be effective.o
+this tool to be effective.
 
 Once the files are locked into memory and the cache is hot the program puts
 itself to sleep until a signal arrives. Once the program is sleeping that's it.
 Any changes to the files that'd require to remap the files are not caught by
 fmlock and the cache on any changed or grown pages may become cold over time.
 
+Please note, that memory locking is subject to process limits. See prlimit(2)
+and your system's limits configuration. The information found in pam_limits(8) 
+is applicable to most systems.
+
 The purpose of this is that (large) files can be preloaded into RAM, namely the
 block I/O cache for other processes to read from. This is for example required
 to measure the RAM bandwidth and CPU limited throughput of data processing code,
diff --git a/fmlock.c b/fmlock.c
index fa4f3c9..45bb419 100644
--- a/fmlock.c
+++ b/fmlock.c
@@ -1,6 +1,7 @@
 #include <sys/types.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <sys/resource.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <stddef.h>
@@ -26,24 +27,41 @@ int heat_the_cache(int fd)
 
 int main(int argc, char *argv[])
 {
-	int i, fd_null, n_fileslocked;
+	unsigned long long locked_memory;
+	int i, fd_null;
 	fd_set phony_fdset;
-	char *buf;
+	struct rlimit mlock_limit;
 
 	if( 2 > argc ) {
 		fprintf(stderr,
-			"Usage:\n%s [filenames]\n",
+			"Usage:\n\n"
+			"%s [filenames]\n\n"
+			"Once its deed is done kill the process by sending a terminating signal.\n"
+			"SIGINT (Ctrl+C) on the controlling terminal should do the trick.\n",
 			argv[0] );
 		return 1;
 	}
 
-	n_fileslocked = 0;
+	if( -1 == getrlimit(RLIMIT_MEMLOCK, &mlock_limit) ) {
+		fprintf(stderr,
+			"error getrlimit(RLIMIT_MEMLOCK): %s\n",
+			strerror(errno) );
+		return 1;
+	}
+	fprintf(stderr,
+		"memlock rlimit: %llu\n",
+		(unsigned long long)mlock_limit.rlim_cur );
+
+	locked_memory = 0;
 	for(i = 1; i < argc; ++i) {
 		char const * const filename = argv[i];
 		int fd;
 		struct stat st;
 		void *ptr;
 
+		fprintf(stderr,
+			"mlocking '%s'... ", filename);
+
 	retry_open:
 		fd = open(filename, O_RDONLY);
 		if( -1 == fd ) {
@@ -67,6 +85,19 @@ int main(int argc, char *argv[])
 			goto finish_file;
 		}
 
+		if( locked_memory + st.st_size > mlock_limit.rlim_cur ) {
+			fprintf(stderr,
+				"error: exceeded the memlock resource limit for this process.\n"
+				"Required limit to mlock '%s': %llu (counting already mlocked files)\n"
+				"Locked memory resource limit set to: %llu\n"
+				"Increase the locked memory resource limit and try again.\n",
+				filename,
+				(unsigned long long)locked_memory + st.st_size,
+				(unsigned long long)mlock_limit.rlim_cur );
+			close(fd);
+			break;
+		}
+
 		ptr = mmap(
 			NULL,
 			st.st_size,
@@ -91,19 +122,31 @@ int main(int argc, char *argv[])
 				strerror(errno) );
 			goto finish_file;
 		}
-		++n_fileslocked;
+
+		if( locked_memory + st.st_size < locked_memory ) {
+			/* overflow */
+			locked_memory = -1;
+		} else
+		{
+			locked_memory += st.st_size;
+		}
 
 		heat_the_cache(fd);
 
 	finish_file:
 		close(fd);
+		fputs("done\n", stderr);
 	}
 
-	if( !n_fileslocked ) {
+	if( !locked_memory ) {
+		fprintf(stderr,
+			"nothing locked, exiting.\n");
 		return 1;
 	}
 
-	fprintf(stderr, "Files locked and cache heated up. Going to sleep, .zZ...\n");
+	fprintf(stderr,
+		"Files locked and cache heated up. pid=%lld. Going to sleep, .zZ...\n",
+		(long long)getpid() );
 
 	/* At this point the program shall sleep until a terminating
 	 * signal arrives. To do so a nice side effect of the definition
-- 
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