Commit 5abd85f6 authored by Baokun Li's avatar Baokun Li Committed by Theodore Ts'o
Browse files

ext4: factor out ext4_mb_might_prefetch() 



Extract ext4_mb_might_prefetch() to make the code clearer and to
prepare for the later conversion of 'choose group' to 'scan groups'.
No functional changes.

Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarZhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-14-libaokun1@huawei.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 45704f92

fs/ext4/mballoc.c

+38 −24
Original line number Diff line number Diff line
@@ -2781,6 +2781,37 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group, 
	return group;

}



/*

 * Batch reads of the block allocation bitmaps to get

 * multiple READs in flight; limit prefetching at inexpensive

 * CR, otherwise mballoc can spend a lot of time loading

 * imperfect groups

 */

static void ext4_mb_might_prefetch(struct ext4_allocation_context *ac,

				   ext4_group_t group)

{

	struct ext4_sb_info *sbi;



	if (ac->ac_prefetch_grp != group)

		return;



	sbi = EXT4_SB(ac->ac_sb);

	if (ext4_mb_cr_expensive(ac->ac_criteria) ||

	    ac->ac_prefetch_ios < sbi->s_mb_prefetch_limit) {

		unsigned int nr = sbi->s_mb_prefetch;



		if (ext4_has_feature_flex_bg(ac->ac_sb)) {

			nr = 1 << sbi->s_log_groups_per_flex;

			nr -= group & (nr - 1);

			nr = umin(nr, sbi->s_mb_prefetch);

		}



		ac->ac_prefetch_nr = nr;

		ac->ac_prefetch_grp = ext4_mb_prefetch(ac->ac_sb, group, nr,

						       &ac->ac_prefetch_ios);

	}

}



/*

 * Prefetching reads the block bitmap into the buffer cache; but we

 * need to make sure that the buddy bitmap in the page cache has been
@@ -2817,10 +2848,9 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, 
static noinline_for_stack int

ext4_mb_regular_allocator(struct ext4_allocation_context *ac)

{

	ext4_group_t prefetch_grp = 0, ngroups, group, i;

	ext4_group_t ngroups, group, i;

	enum criteria new_cr, cr = CR_GOAL_LEN_FAST;

	int err = 0, first_err = 0;

	unsigned int nr = 0, prefetch_ios = 0;

	struct ext4_sb_info *sbi;

	struct super_block *sb;

	struct ext4_buddy e4b;
@@ -2881,6 +2911,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) 
		cr = CR_POWER2_ALIGNED;



	ac->ac_e4b = &e4b;

	ac->ac_prefetch_ios = 0;

repeat:

	for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) {

		ac->ac_criteria = cr;
@@ -2890,8 +2921,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) 
		 */

		group = ac->ac_g_ex.fe_group;

		ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;

		prefetch_grp = group;

		nr = 0;

		ac->ac_prefetch_grp = group;

		ac->ac_prefetch_nr = 0;



		for (i = 0, new_cr = cr; i < ngroups; i++,

		     ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
@@ -2903,24 +2934,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) 
				goto repeat;

			}



			/*

			 * Batch reads of the block allocation bitmaps

			 * to get multiple READs in flight; limit

			 * prefetching at inexpensive CR, otherwise mballoc

			 * can spend a lot of time loading imperfect groups

			 */

			if ((prefetch_grp == group) &&

			    (ext4_mb_cr_expensive(cr) ||

			     prefetch_ios < sbi->s_mb_prefetch_limit)) {

				nr = sbi->s_mb_prefetch;

				if (ext4_has_feature_flex_bg(sb)) {

					nr = 1 << sbi->s_log_groups_per_flex;

					nr -= group & (nr - 1);

					nr = min(nr, sbi->s_mb_prefetch);

				}

				prefetch_grp = ext4_mb_prefetch(sb, group,

							nr, &prefetch_ios);

			}

			ext4_mb_might_prefetch(ac, group);



			/* prevent unnecessary buddy loading. */

			if (cr < CR_ANY_FREE &&
@@ -3018,8 +3032,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) 
		 ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status,

		 ac->ac_flags, cr, err);



	if (nr)

		ext4_mb_prefetch_fini(sb, prefetch_grp, nr);

	if (ac->ac_prefetch_nr)

		ext4_mb_prefetch_fini(sb, ac->ac_prefetch_grp, ac->ac_prefetch_nr);



	return err;

}

fs/ext4/mballoc.h

+4 −0
Original line number Diff line number Diff line
@@ -192,6 +192,10 @@ struct ext4_allocation_context { 
	 */

	ext4_grpblk_t	ac_orig_goal_len;



	ext4_group_t ac_prefetch_grp;

	unsigned int ac_prefetch_ios;

	unsigned int ac_prefetch_nr;



	__u32 ac_flags;		/* allocation hints */

	__u32 ac_groups_linear_remaining;

	__u16 ac_groups_scanned;