xfs: add debug knobs to control btree bulk load slack factors

Add some debug knobs so that we can control the leaf and node block
slack when rebuilding btrees.

For developers, it might be useful to construct btrees of various
heights by crafting a filesystem with a certain number of records and
then using repair+knobs to rebuild the index with a certain shape.
Practically speaking, you'd only ever do that for extreme stress
testing of the runtime code or the btree generator.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/scrub/newbt.c b/fs/xfs/scrub/newbt.c
index 992cf34..4688360 100644 (file)
--- a/fs/xfs/scrub/newbt.c
+++ b/fs/xfs/scrub/newbt.c
@@ -32,6 +32,7 @@
  * btree bulk loading code calculates for us.  However, there are some
  * exceptions to this rule:
  *
+ * (0) If someone turned one of the debug knobs.
  * (1) If this is a per-AG btree and the AG has less than 10% space free.
  * (2) If this is an inode btree and the FS has less than 10% space free.
 
@@ -47,9 +48,13 @@ xrep_newbt_estimate_slack(
        uint64_t                free;
        uint64_t                sz;
 
-       /* Let the btree code compute the default slack values. */
-       bload->leaf_slack = -1;
-       bload->node_slack = -1;
+       /*
+        * The xfs_globals values are set to -1 (i.e. take the bload defaults)
+        * unless someone has set them otherwise, so we just pull the values
+        * here.
+        */
+       bload->leaf_slack = xfs_globals.bload_leaf_slack;
+       bload->node_slack = xfs_globals.bload_node_slack;
 
        if (sc->ops->type == ST_PERAG) {
                free = sc->sa.pag->pagf_freeblks;

diff --git a/fs/xfs/xfs_globals.c b/fs/xfs/xfs_globals.c
index 9edc1f2..f18fec0 100644 (file)
--- a/fs/xfs/xfs_globals.c
+++ b/fs/xfs/xfs_globals.c
@@ -44,4 +44,16 @@ struct xfs_globals xfs_globals = {
        .pwork_threads          =       -1,     /* automatic thread detection */
        .larp                   =       false,  /* log attribute replay */
 #endif
+
+       /*
+        * Leave this many record slots empty when bulk loading btrees.  By
+        * default we load new btree leaf blocks 75% full.
+        */
+       .bload_leaf_slack       =       -1,
+
+       /*
+        * Leave this many key/ptr slots empty when bulk loading btrees.  By
+        * default we load new btree node blocks 75% full.
+        */
+       .bload_node_slack       =       -1,
 };

diff --git a/fs/xfs/xfs_sysctl.h b/fs/xfs/xfs_sysctl.h
index f78ad6b..276696a 100644 (file)
--- a/fs/xfs/xfs_sysctl.h
+++ b/fs/xfs/xfs_sysctl.h
@@ -85,6 +85,8 @@ struct xfs_globals {
        int     pwork_threads;          /* parallel workqueue threads */
        bool    larp;                   /* log attribute replay */
 #endif
+       int     bload_leaf_slack;       /* btree bulk load leaf slack */
+       int     bload_node_slack;       /* btree bulk load node slack */
        int     log_recovery_delay;     /* log recovery delay (secs) */
        int     mount_delay;            /* mount setup delay (secs) */
        bool    bug_on_assert;          /* BUG() the kernel on assert failure */

diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
index 871f16a..1748566 100644 (file)
--- a/fs/xfs/xfs_sysfs.c
+++ b/fs/xfs/xfs_sysfs.c
@@ -262,6 +262,58 @@ larp_show(
 XFS_SYSFS_ATTR_RW(larp);
 #endif /* DEBUG */
 
+STATIC ssize_t
+bload_leaf_slack_store(
+       struct kobject  *kobject,
+       const char      *buf,
+       size_t          count)
+{
+       int             ret;
+       int             val;
+
+       ret = kstrtoint(buf, 0, &val);
+       if (ret)
+               return ret;
+
+       xfs_globals.bload_leaf_slack = val;
+       return count;
+}
+
+STATIC ssize_t
+bload_leaf_slack_show(
+       struct kobject  *kobject,
+       char            *buf)
+{
+       return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.bload_leaf_slack);
+}
+XFS_SYSFS_ATTR_RW(bload_leaf_slack);
+
+STATIC ssize_t
+bload_node_slack_store(
+       struct kobject  *kobject,
+       const char      *buf,
+       size_t          count)
+{
+       int             ret;
+       int             val;
+
+       ret = kstrtoint(buf, 0, &val);
+       if (ret)
+               return ret;
+
+       xfs_globals.bload_node_slack = val;
+       return count;
+}
+
+STATIC ssize_t
+bload_node_slack_show(
+       struct kobject  *kobject,
+       char            *buf)
+{
+       return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.bload_node_slack);
+}
+XFS_SYSFS_ATTR_RW(bload_node_slack);
+
 static struct attribute *xfs_dbg_attrs[] = {
        ATTR_LIST(bug_on_assert),
        ATTR_LIST(log_recovery_delay),
@@ -271,6 +323,8 @@ static struct attribute *xfs_dbg_attrs[] = {
        ATTR_LIST(pwork_threads),
        ATTR_LIST(larp),
 #endif
+       ATTR_LIST(bload_leaf_slack),
+       ATTR_LIST(bload_node_slack),
        NULL,
 };
 ATTRIBUTE_GROUPS(xfs_dbg);