[XFS] Add xfs_rotorstep sysctl for controlling placement of extents for

new files by the inode32 allocator.

SGI-PV: 912624
SGI-Modid: xfs-linux:xfs-kern:181032a
Signed-off-by: Geoffrey Wehrman <gwehrman@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>

fs/xfs/linux-2.6/xfs_globals.c

@@ -64,6 +64,7 @@ xfs_param_t xfs_params = {
 	.xfs_buf_timer	= {	100/2,		1*100,		30*100	},
 	.xfs_buf_age	= {	1*100,		15*100,		7200*100},
 	.inherit_nosym	= {	0,		0,		1	},
+	.rotorstep	= {	1,		1,		255	},
 };
 
 /*

fs/xfs/linux-2.6/xfs_linux.h

@@ -142,6 +142,7 @@ static inline void set_buffer_unwritten_io(struct buffer_head *bh)
 #define xfs_buf_timer_centisecs	xfs_params.xfs_buf_timer.val
 #define xfs_buf_age_centisecs	xfs_params.xfs_buf_age.val
 #define xfs_inherit_nosymlinks	xfs_params.inherit_nosym.val
+#define xfs_rotorstep		xfs_params.rotorstep.val
 
 #define current_cpu()		smp_processor_id()
 #define current_pid()		(current->pid)

fs/xfs/linux-2.6/xfs_sysctl.c

@@ -134,6 +134,11 @@ STATIC ctl_table xfs_table[] = {
 	&sysctl_intvec, NULL,
 	&xfs_params.inherit_nosym.min, &xfs_params.inherit_nosym.max},
 
+	{XFS_ROTORSTEP, "rotorstep", &xfs_params.rotorstep.val,
+	sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+	&sysctl_intvec, NULL, 
+	&xfs_params.rotorstep.min, &xfs_params.rotorstep.max},
+
 	/* please keep this the last entry */
 #ifdef CONFIG_PROC_FS
 	{XFS_STATS_CLEAR, "stats_clear", &xfs_params.stats_clear.val,

fs/xfs/linux-2.6/xfs_sysctl.h

@@ -60,6 +60,7 @@ typedef struct xfs_param {
 	xfs_sysctl_val_t xfs_buf_timer;	/* Interval between xfsbufd wakeups. */
 	xfs_sysctl_val_t xfs_buf_age;	/* Metadata buffer age before flush. */
 	xfs_sysctl_val_t inherit_nosym;	/* Inherit the "nosymlinks" flag. */
+	xfs_sysctl_val_t rotorstep;	/* inode32 AG rotoring control knob */
 } xfs_param_t;
 
 /*
@@ -97,6 +98,7 @@ enum {
 	XFS_BUF_AGE = 17,
 	/* XFS_IO_BYPASS = 18 */
 	XFS_INHERIT_NOSYM = 19,
+	XFS_ROTORSTEP = 20,
 };
 
 extern xfs_param_t	xfs_params;

fs/xfs/xfs_alloc.c

@@ -2247,6 +2247,7 @@ xfs_alloc_vextent(
 	xfs_alloctype_t	type;	/* input allocation type */
 	int		bump_rotor = 0;
 	int		no_min = 0;
+	xfs_agnumber_t	rotorstep = xfs_rotorstep; /* inode32 agf stepper */
 
 	mp = args->mp;
 	type = args->otype = args->type;
@@ -2310,7 +2311,9 @@ xfs_alloc_vextent(
 		 */
 		if ((args->userdata  == XFS_ALLOC_INITIAL_USER_DATA) &&
 		    (mp->m_flags & XFS_MOUNT_32BITINODES)) {
-			args->fsbno = XFS_AGB_TO_FSB(mp, mp->m_agfrotor, 0);
+			args->fsbno = XFS_AGB_TO_FSB(mp,
+					((mp->m_agfrotor / rotorstep) %
+					mp->m_sb.sb_agcount), 0);
 			bump_rotor = 1;
 		}
 		args->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
@@ -2326,7 +2329,8 @@ xfs_alloc_vextent(
 			/*
 			 * Start with the last place we left off.
 			 */
-			args->agno = sagno = mp->m_agfrotor;
+			args->agno = sagno = (mp->m_agfrotor / rotorstep) %
+					mp->m_sb.sb_agcount;
 			args->type = XFS_ALLOCTYPE_THIS_AG;
 			flags = XFS_ALLOC_FLAG_TRYLOCK;
 		} else if (type == XFS_ALLOCTYPE_FIRST_AG) {
@@ -2400,8 +2404,14 @@ xfs_alloc_vextent(
 			}
 		}
 		up_read(&mp->m_peraglock);
-		if (bump_rotor || (type == XFS_ALLOCTYPE_ANY_AG))
-			mp->m_agfrotor = (args->agno + 1) % mp->m_sb.sb_agcount;
+		if (bump_rotor || (type == XFS_ALLOCTYPE_ANY_AG)) {
+			if (args->agno == sagno)
+				mp->m_agfrotor = (mp->m_agfrotor + 1) %
+					(mp->m_sb.sb_agcount * rotorstep);
+			else
+				mp->m_agfrotor = (args->agno * rotorstep + 1) %
+					(mp->m_sb.sb_agcount * rotorstep);
+		}
 		break;
 	default:
 		ASSERT(0);