[PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap

[Kundan Kumar <kundan.kumar@samsung.com>]

Add per-inode structures to track predicted AGs of dirty folios using
an xarray and bitmap. This enables efficient identification of AGs
involved in writeback.

Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/xfs/xfs_icache.c | 27 +++++++++++++++++++++++++++
 fs/xfs/xfs_inode.h  |  5 +++++
 2 files changed, 32 insertions(+)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index e44040206851..f97aa6d66271 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -80,6 +80,25 @@ static inline xa_mark_t ici_tag_to_mark(unsigned int tag)
 	return XFS_PERAG_BLOCKGC_MARK;
 }
 
+static int xfs_inode_init_ag_bitmap(struct xfs_inode *ip)
+{
+	unsigned int bits = ip->i_mount->m_sb.sb_agcount;
+	unsigned int nlongs;
+
+	xa_init_flags(&ip->i_ag_pmap, XA_FLAGS_LOCK_IRQ);
+	ip->i_ag_dirty_bitmap = NULL;
+	ip->i_ag_dirty_bits = bits;
+
+	if (!bits)
+		return 0;
+
+	nlongs = BITS_TO_LONGS(bits);
+	ip->i_ag_dirty_bitmap = kcalloc(nlongs, sizeof(unsigned long),
+					GFP_NOFS);
+
+	return ip->i_ag_dirty_bitmap ? 0 : -ENOMEM;
+}
+
 /*
  * Allocate and initialise an xfs_inode.
  */
@@ -131,6 +150,8 @@ xfs_inode_alloc(
 	ip->i_next_unlinked = NULLAGINO;
 	ip->i_prev_unlinked = 0;
 
+	xfs_inode_init_ag_bitmap(ip);
+
 	return ip;
 }
 
@@ -194,6 +215,12 @@ xfs_inode_free(
 	ip->i_ino = 0;
 	spin_unlock(&ip->i_flags_lock);
 
+	/* free xarray contents (values are immediate packed ints) */
+	xa_destroy(&ip->i_ag_pmap);
+	kfree(ip->i_ag_dirty_bitmap);
+	ip->i_ag_dirty_bitmap = NULL;
+	ip->i_ag_dirty_bits = 0;
+
 	__xfs_inode_free(ip);
 }
 
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index bd6d33557194..dee449168605 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -99,6 +99,11 @@ typedef struct xfs_inode {
 	spinlock_t		i_ioend_lock;
 	struct work_struct	i_ioend_work;
 	struct list_head	i_ioend_list;
+
+	/* AG prediction map: pgoff_t -> packed u32 */
+	struct xarray           i_ag_pmap;
+	unsigned long           *i_ag_dirty_bitmap;
+	unsigned int            i_ag_dirty_bits;
 } xfs_inode_t;
 
 static inline bool xfs_inode_on_unlinked_list(const struct xfs_inode *ip)
-- 
2.25.1