ext4: Remove the logic to trim inode PAs

Earlier, inode PAs were stored in a linked list. This caused a need to
periodically trim the list down inorder to avoid growing it to a very
large size, as this would severly affect performance during list
iteration.

Recent patches changed this list to an rbtree, and since the tree scales
up much better, we no longer need to have the trim functionality, hence
remove it.

Signed-off-by: Ojaswin Mujoo <[e-mail]>
Reviewed-by: Ritesh Harjani (IBM) <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

Documentation/admin-guide/ext4.rst

···
         multiple of this tuning parameter if the stripe size is not set in the
         ext4 superblock
 
-  mb_max_inode_prealloc
-        The maximum length of per-inode ext4_prealloc_space list.
-
   mb_max_to_scan
         The maximum number of extents the multiblock allocator will search to
         find the best extent.

fs/ext4/ext4.h

···
 	unsigned int s_mb_stats;
 	unsigned int s_mb_order2_reqs;
 	unsigned int s_mb_group_prealloc;
-	unsigned int s_mb_max_inode_prealloc;
 	unsigned int s_max_dir_size_kb;
 	/* where last allocation was done - for stream allocation */
 	unsigned long s_mb_last_group;

fs/ext4/mballoc.c

···
 	sbi->s_mb_stats = MB_DEFAULT_STATS;
 	sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
 	sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
-	sbi->s_mb_max_inode_prealloc = MB_DEFAULT_MAX_INODE_PREALLOC;
 	/*
 	 * The default group preallocation is 512, which for 4k block
 	 * sizes translates to 2 megabytes.  However for bigalloc file
···
 }
 
 /*
- * if per-inode prealloc list is too long, trim some PA
- */
-static void ext4_mb_trim_inode_pa(struct inode *inode)
-{
-	struct ext4_inode_info *ei = EXT4_I(inode);
-	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
-	int count, delta;
-
-	count = atomic_read(&ei->i_prealloc_active);
-	delta = (sbi->s_mb_max_inode_prealloc >> 2) + 1;
-	if (count > sbi->s_mb_max_inode_prealloc + delta) {
-		count -= sbi->s_mb_max_inode_prealloc;
-		ext4_discard_preallocations(inode, count);
-	}
-}
-
-/*
  * release all resource we used in allocation
  */
 static int ext4_mb_release_context(struct ext4_allocation_context *ac)
 {
-	struct inode *inode = ac->ac_inode;
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
 	struct ext4_prealloc_space *pa = ac->ac_pa;
 	if (pa) {
···
 	if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
 		mutex_unlock(&ac->ac_lg->lg_mutex);
 	ext4_mb_collect_stats(ac);
-	ext4_mb_trim_inode_pa(inode);
 	return 0;
 }
 

fs/ext4/mballoc.h

···
 #define MB_DEFAULT_GROUP_PREALLOC	512
 
 /*
- * maximum length of inode prealloc list
- */
-#define MB_DEFAULT_MAX_INODE_PREALLOC	512
-
-/*
  * Number of groups to search linearly before performing group scanning
  * optimization.
  */

fs/ext4/sysfs.c

···
 EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
 EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
 EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
-EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
 EXT4_RW_ATTR_SBI_UI(mb_max_linear_groups, s_mb_max_linear_groups);
 EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
 EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
···
 	ATTR_LIST(mb_order2_req),
 	ATTR_LIST(mb_stream_req),
 	ATTR_LIST(mb_group_prealloc),
-	ATTR_LIST(mb_max_inode_prealloc),
 	ATTR_LIST(mb_max_linear_groups),
 	ATTR_LIST(max_writeback_mb_bump),
 	ATTR_LIST(extent_max_zeroout_kb),