From c86b6a2c769c821a64fc14c62a953244b41cb190 Mon Sep 17 00:00:00 2001
From: Eric Wong <normalperson@yhbt.net>
Date: Fri, 21 Jun 2013 03:34:20 +0000
Subject: dev: shrink and cache-align struct mog_dev

We will have structures inside the dev struct accessed by multiple
threads frequently, so keep it cache-aligned.

To reduce memory usage for large-numbered devices, avoid storing the
prefix on output and instead just rely on the printf-family of
routines to generate stringified output in uncommon code paths.
---
 cmogstored.h   |  1 -
 dev.c          | 44 +++++++++++++++++++++++++-------------------
 path_parser.rl |  2 +-
 3 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/cmogstored.h b/cmogstored.h
index 1134827..66193b7 100644
--- a/cmogstored.h
+++ b/cmogstored.h
@@ -100,7 +100,6 @@ struct mog_wbuf;
 struct mog_dev {
 	dev_t st_dev;
 	uint32_t devid;
-	char prefix[FLEXIBLE_ARRAY_MEMBER];
 };
 
 struct mog_rbuf {
diff --git a/dev.c b/dev.c
index 7454b2d..cd39c5d 100644
--- a/dev.c
+++ b/dev.c
@@ -4,25 +4,31 @@
  */
 #include "cmogstored.h"
 
+static int stat_prefix(struct mog_svc *svc, struct stat *sb, uint32_t mog_devid)
+{
+	char prefix[sizeof("/dev" MOG_STR(MOG_DEVID_MAX) "/")];
+	int rc;
+
+	assert(mog_devid <= MOG_DEVID_MAX && "mog_devid not filtered");
+	rc = snprintf(prefix, sizeof(prefix), "/dev%u/", mog_devid);
+	assert(rc > 0 && rc < (int)sizeof(prefix) && "we suck at snprintf");
+
+	return mog_stat(svc, prefix, sb);
+}
+
 static struct mog_dev *mog_dev_new(struct mog_svc *svc, uint32_t mog_devid)
 {
 	struct mog_dev *dev;
 	struct stat sb;
-	char *devprefix = xasprintf("/dev%u/", mog_devid);
-	size_t len = strlen(devprefix);
 
-	if (mog_stat(svc, devprefix, &sb) < 0) {
-		PRESERVE_ERRNO( free(devprefix) );
+	/* we have no space on stack */
+	if (mog_devid > MOG_DEVID_MAX)
 		return NULL;
-	}
 
-	dev = xmalloc(sizeof(struct mog_dev) + len);
-
-	assert(devprefix[len - 1] == '/' && "not trailing slash");
-	devprefix[len - 1] = '\0';
-	memcpy(dev->prefix, devprefix, len);
-	free(devprefix);
+	if (stat_prefix(svc, &sb, mog_devid) < 0)
+		return NULL;
 
+	dev = mog_cachealign(sizeof(struct mog_dev));
 	dev->devid = mog_devid;
 	dev->st_dev = sb.st_dev;
 
@@ -46,7 +52,7 @@ struct mog_dev *mog_dev_for(struct mog_svc *svc, uint32_t mog_devid)
 		 * Possible FS/device error, it could come back, so do
 		 * not remove here.
 		 */
-		if (mog_stat(svc, ret->prefix, &sb) < 0)
+		if (stat_prefix(svc, &sb, ret->devid) < 0)
 			goto out;
 
 		/* st_dev may change due to remount, update if needed */
@@ -112,7 +118,7 @@ const struct mog_dev *dev, struct mog_svc *svc, int fd, struct statvfs *v)
 		static const char usage_fmt[] =
 			"available: %llu\n"
 			"device: %s\n"
-			"disk: %s%s\n"
+			"disk: %s/dev%u\n"
 			"time: %lld\n"
 			"total: %llu\n"
 			"use: %u%%\n"
@@ -121,18 +127,18 @@ const struct mog_dev *dev, struct mog_svc *svc, int fd, struct statvfs *v)
 		errno = 0;
 		rc = dprintf(fd, usage_fmt,
 			     available, me->me_devname, svc->docroot,
-			     dev->prefix, now, total, use, used);
+			     (unsigned)dev->devid, now, total, use, used);
 
 		PRESERVE_ERRNO( mog_mnt_release(me) );
 		if (rc < 0 || errno == ENOSPC) {
 			PRESERVE_ERRNO(do {
-				syslog(LOG_ERR, "dprintf(%s%s/usage): %m",
-				       svc->docroot, dev->prefix);
+				syslog(LOG_ERR, "dprintf(%s/dev%u/usage): %m",
+				       svc->docroot, (unsigned)dev->devid);
 			} while (0));
 		}
 	} else {
-		syslog(LOG_ERR, "mount entry not found for %s%s",
-		       svc->docroot, dev->prefix);
+		syslog(LOG_ERR, "mount entry not found for %s/dev%u",
+		       svc->docroot, (unsigned)dev->devid);
 		errno = ENODEV;
 	}
 
@@ -149,7 +155,7 @@ int mog_dev_mkusage(const struct mog_dev *dev, struct mog_svc *svc)
 	if (!svc->mgmt_mfd)
 		return 0;
 
-	usage_path = xasprintf("%s/usage", dev->prefix);
+	usage_path = xasprintf("/dev%u/usage", (unsigned)dev->devid);
 	tmp_path = xasprintf("%s.%x", usage_path, (unsigned)getpid());
 
 	if (mog_unlink(svc, tmp_path) < 0 && errno != ENOENT) goto out;
diff --git a/path_parser.rl b/path_parser.rl
index fc77c98..e403607 100644
--- a/path_parser.rl
+++ b/path_parser.rl
@@ -11,7 +11,7 @@
 
 	devid = "dev"
 		(digit+) $ {
-			/* no overflow checking here, no need */
+			/* no overflow checking here, we do it in mog_dev_new */
 			*mog_devid *= 10;
 			*mog_devid += fc - '0';
 		}
-- 
cgit v1.2.3-24-ge0c7