【小ネタ】Linux 6.15でExFATのファイル削除が高速化された話

int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
{
	int i, b;
	unsigned int ent_idx;
	struct super_block *sb = inode->i_sb;
	struct exfat_sb_info *sbi = EXFAT_SB(sb);
	struct exfat_mount_options *opts = &sbi->options;

	if (!is_valid_cluster(sbi, clu))
		return -EIO;

	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);

	if (!test_bit_le(b, sbi->vol_amap[i]->b_data))
		return -EIO;

	clear_bit_le(b, sbi->vol_amap[i]->b_data);

	exfat_update_bh(sbi->vol_amap[i], sync);

	if (opts->discard) {
		int ret_discard;

		ret_discard = sb_issue_discard(sb,
			exfat_cluster_to_sector(sbi, clu),
			(1 << sbi->sect_per_clus_bits), GFP_NOFS, 0);

		if (ret_discard == -EOPNOTSUPP) {
			exfat_err(sb, "discard not supported by device, disabling");
			opts->discard = 0;
		}
	}

	return 0;
}

/* This function must be called with bitmap_lock held */
static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
{
	struct super_block *sb = inode->i_sb;
	struct exfat_sb_info *sbi = EXFAT_SB(sb);
	int cur_cmap_i, next_cmap_i;
	unsigned int num_clusters = 0;
	unsigned int clu;
...
	if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
		int err;
		unsigned int last_cluster = p_chain->dir + p_chain->size - 1;
		do {
			bool sync = false;

			if (clu < last_cluster)
				next_cmap_i =
				  BITMAP_OFFSET_SECTOR_INDEX(sb, CLUSTER_TO_BITMAP_ENT(clu+1));

			/* flush bitmap only if index would be changed or for last cluster */
			if (clu == last_cluster || cur_cmap_i != next_cmap_i) {
				sync = true;
				cur_cmap_i = next_cmap_i;
			}

			err = exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode)));
			if (err)
				break;
			clu++;
			num_clusters++;
		} while (num_clusters < p_chain->size);
	} else {
		do {
			bool sync = false;
			unsigned int n_clu = clu;
			int err = exfat_get_next_cluster(sb, &n_clu);

			if (err || n_clu == EXFAT_EOF_CLUSTER)
				sync = true;
			else
				next_cmap_i =
				  BITMAP_OFFSET_SECTOR_INDEX(sb, CLUSTER_TO_BITMAP_ENT(n_clu));

			if (cur_cmap_i != next_cmap_i) {
				sync = true;
				cur_cmap_i = next_cmap_i;
			}

			if (exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode))))
				break;
			clu = n_clu;
			num_clusters++;

			if (err)
				break;

			if (num_clusters >= sbi->num_clusters - EXFAT_FIRST_CLUSTER) {
				/*
				 * The cluster chain includes a loop, scan the
				 * bitmap to get the number of used clusters.
				 */
				exfat_count_used_clusters(sb, &sbi->used_clusters);

				return 0;
			}
		} while (clu != EXFAT_EOF_CLUSTER);
	}

	sbi->used_clusters -= num_clusters;
	return 0;
}

int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
{
	int i, b;
	unsigned int ent_idx;
	struct super_block *sb = inode->i_sb;
	struct exfat_sb_info *sbi = EXFAT_SB(sb);
...
	if (opts->discard) {
...
		ret_discard = sb_issue_discard(sb,
			exfat_cluster_to_sector(sbi, clu),
			(1 << sbi->sect_per_clus_bits), GFP_NOFS, 0);
...
}

static inline int sb_issue_discard(struct super_block *sb, sector_t block,
		sector_t nr_blocks, gfp_t gfp_mask, unsigned long flags)
{
	return blkdev_issue_discard(sb->s_bdev,
				    block << (sb->s_blocksize_bits -
					      SECTOR_SHIFT),
				    nr_blocks << (sb->s_blocksize_bits -
						  SECTOR_SHIFT),
				    gfp_mask);
}

/**
 * blkdev_issue_discard - queue a discard
 * @bdev:	blockdev to issue discard for
 * @sector:	start sector
 * @nr_sects:	number of sectors to discard
 * @gfp_mask:	memory allocation flags (for bio_alloc)
 *
 * Description:
 *    Issue a discard request for the sectors in question.
 */
int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
		sector_t nr_sects, gfp_t gfp_mask)
{
	struct bio *bio = NULL;
	struct blk_plug plug;
	int ret;

	blk_start_plug(&plug);
	ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, &bio);
	if (!ret && bio) {
		ret = submit_bio_wait(bio);
		if (ret == -EOPNOTSUPP)
			ret = 0;
		bio_put(bio);
	}
	blk_finish_plug(&plug);

	return ret;
}

// fs/exfat/exfat_raw.h
/* EXFAT: Main and Backup Boot Sector (512 bytes) */
struct boot_sector {
	__u8	jmp_boot[BOOTSEC_JUMP_BOOT_LEN];
	__u8	fs_name[BOOTSEC_FS_NAME_LEN];
	__u8	must_be_zero[BOOTSEC_OLDBPB_LEN];
	__le64	partition_offset;
	__le64	vol_length;
	__le32	fat_offset;
	__le32	fat_length;
	__le32	clu_offset;
	__le32	clu_count;
	__le32	root_cluster;
	__le32	vol_serial;
	__u8	fs_revision[2];
	__le16	vol_flags;
	__u8	sect_size_bits;
	__u8	sect_per_clus_bits;
	__u8	num_fats;
	__u8	drv_sel;
	__u8	percent_in_use;
	__u8	reserved[7];
	__u8	boot_code[390];
	__le16	signature;
} __packed;

// fs/exfat/super.c
if (p_boot->sect_per_clus_bits > EXFAT_MAX_SECT_PER_CLUS_BITS(p_boot)) {
	exfat_err(sb, "bogus sectors bits per cluster : %u",
			p_boot->sect_per_clus_bits);
	return -EINVAL;
}
sbi->sect_per_clus_bits = p_boot->sect_per_clus_bits;

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index 9ff825f1502d..cc01556c9d9b 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -147,7 +147,6 @@  int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 	unsigned int ent_idx;
 	struct super_block *sb = inode->i_sb;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
-	struct exfat_mount_options *opts = &sbi->options;
 
 	if (!is_valid_cluster(sbi, clu))
 		return -EIO;
@@ -163,19 +162,6 @@  int exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 
 	exfat_update_bh(sbi->vol_amap[i], sync);
 
-	if (opts->discard) {
-		int ret_discard;
-
-		ret_discard = sb_issue_discard(sb,
-			exfat_cluster_to_sector(sbi, clu),
-			(1 << sbi->sect_per_clus_bits), GFP_NOFS, 0);
-
-		if (ret_discard == -EOPNOTSUPP) {
-			exfat_err(sb, "discard not supported by device, disabling");
-			opts->discard = 0;
-		}
-	}
-
 	return 0;
 }

 diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
index 6f3651c6ca91..b9473a69f104 100644
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -144,6 +144,20 @@  int exfat_chain_cont_cluster(struct super_block *sb, unsigned int chain,
 	return 0;
 }
 
+static inline void exfat_discard_cluster(struct super_block *sb,
+		unsigned int clu, unsigned int num_clusters)
+{
+	int ret;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+
+	ret = sb_issue_discard(sb, exfat_cluster_to_sector(sbi, clu),
+			sbi->sect_per_clus * num_clusters, GFP_NOFS, 0);
+	if (ret == -EOPNOTSUPP) {
+		exfat_err(sb, "discard not supported by device, disabling");
+		sbi->options.discard = 0;
+	}
+}
+
 /* This function must be called with bitmap_lock held */
 static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
 {
@@ -196,7 +210,12 @@  static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 			clu++;
 			num_clusters++;
 		} while (num_clusters < p_chain->size);
+
+		if (sbi->options.discard)
+			exfat_discard_cluster(sb, p_chain->dir, p_chain->size);
 	} else {
+		unsigned int nr_clu = 1;
+
 		do {
 			bool sync = false;
 			unsigned int n_clu = clu;
@@ -215,6 +234,16 @@  static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain
 
 			if (exfat_clear_bitmap(inode, clu, (sync && IS_DIRSYNC(inode))))
 				break;
+
+			if (sbi->options.discard) {
+				if (n_clu == clu + 1)
+					nr_clu++;
+				else {
+					exfat_discard_cluster(sb, clu - nr_clu + 1, nr_clu);
+					nr_clu = 1;
+				}
+			}
+
 			clu = n_clu;
 			num_clusters++;