[Linux-cachefs] [PATCH 1/2] cachefilesd can spin when disk space is short.

[David Howells]

From: NeilBrown <neilb at suse.de>

When cachefilesd finds that it needs to cull, but that culling doesn't
achieve anything, it sets an alarm to wake it in 30 seconds to try again.
But as read_cache_state() will detect that culling is still needed, it will
immediately try again anyway.

This results in 100% cpu usage of no value.

This patch causes culling to be blocked until the 30 second alarm goes off.

It also changes the test to decide whether to enter poll() after blocking
signals to test exactly those values that might be changed by a signal.
Testing these is important, testing anything else is pointless.

Signed-off-by: NeilBrown <neilb at suse.de>
Signed-off-by: David Howells <dhowells at redhat.com>
---

 cachefilesd.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/cachefilesd.c b/cachefilesd.c
index 6658ba5..eaa1bb0 100644
--- a/cachefilesd.c
+++ b/cachefilesd.c
@@ -99,6 +99,7 @@ static struct object **cullready;
 static unsigned nr_in_build_table;
 static unsigned nr_in_ready_table;
 static int ncullable;
+static bool cull_delayed;
 
 
 static const char *configfile = "/etc/cachefilesd.conf";
@@ -246,6 +247,7 @@ static void sigio(int sig)
 static void sigalrm(int sig)
 {
 	jumpstart_scan = true;
+	cull_delayed = false;
 }
 
 /*****************************************************************************/
@@ -613,11 +615,11 @@ static void cachefilesd(void)
 
 		/* sleep without racing on reap and cull with the signal
 		 * handlers */
-		if (!scan && !reap && !cull) {
+		if (!scan && !reap && !(cull && !cull_delayed)) {
 			if (sigprocmask(SIG_BLOCK, &sigs, &osigs) < 0)
 				oserror("Unable to block signals");
 
-			if (!reap && !cull) {
+			if (!reap && !stop && !jumpstart_scan) {
 				if (ppoll(pollfds, 1, NULL, &osigs) < 0 &&
 				    errno != EINTR)
 					oserror("Unable to suspend process");
@@ -644,7 +646,7 @@ static void cachefilesd(void)
 			if (cull) {
 				if (nr_in_ready_table > 0)
 					cull_objects();
-				else if (nr_in_build_table == 0)
+				else if (nr_in_build_table == 0 && !cull_delayed)
 					jumpstart_scan = true;
 			}
 
@@ -1364,6 +1366,7 @@ static void decant_cull_table(void)
 
 	/* if nothing there, scan again in a short while */
 	if (nr_in_build_table == 0) {
+		cull_delayed = true;
 		signal(SIGALRM, sigalrm);
 		alarm(30);
 		return;