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(unknown []) by gzsmtp3 (Coremail) with SMTP id PigvCgB3TegF8oJpYIHPNw--.186S3; Wed, 04 Feb 2026 15:15:20 +0800 (CST) From: Chi Zhiling To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Namjae Jeon , Sungjong Seo , Yuezhang Mo , Chi Zhiling Subject: [PATCH v1 1/3] exfat: add block readahead in exfat_chain_cont_cluster Date: Wed, 4 Feb 2026 15:14:33 +0800 Message-ID: <20260204071435.602246-2-chizhiling@163.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260204071435.602246-1-chizhiling@163.com> References: <20260204071435.602246-1-chizhiling@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:PigvCgB3TegF8oJpYIHPNw--.186S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxWw18GFWftrWUZr1kZryrJFb_yoW5uFWkpa nxCayftrWUGa47Ww4fKw1kJ3Wru3s7Gry5Gry3ur1rAryavrs3ur9rKryFqFWkt3y5Wa1j qF4YvFWjkrZrW37anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jzyIUUUUUU= X-CM-SenderInfo: hfkl6xxlol0wi6rwjhhfrp/xtbC3Am5V2mC8glMpQAA3C From: Chi Zhiling The conversion from NO_FAT_CHAIN format to FAT_CHAIN format occurs when the file cannot allocate contiguous space. When the file to be converted is very large, this process can take a long time. This patch introduces simple readahead to read all the blocks in advance, as these blocks are consecutive. Test in an empty exfat filesystem: dd if=/dev/zero of=/mnt/file bs=1M count=30k dd if=/dev/zero of=/mnt/file2 bs=1M count=1 time cat /mnt/file2 >> /mnt/file | cluster size | before patch | after patch | | ------------ | ------------ | ----------- | | 512 | 47.667s | 4.316s | | 4k | 6.436s | 0.541s | | 32k | 0.758s | 0.071s | | 256k | 0.117s | 0.011s | Signed-off-by: Chi Zhiling --- fs/exfat/exfat_fs.h | 9 +++++++-- fs/exfat/fatent.c | 38 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+), 2 deletions(-) diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h index 2dbed5f8ec26..5a3cdf725846 100644 --- a/fs/exfat/exfat_fs.h +++ b/fs/exfat/exfat_fs.h @@ -10,6 +10,7 @@ #include #include #include +#include #include #define EXFAT_ROOT_INO 1 @@ -79,6 +80,10 @@ enum { #define EXFAT_HINT_NONE -1 #define EXFAT_MIN_SUBDIR 2 +#define EXFAT_BLK_RA_SIZE(sb) \ +(min((sb)->s_bdi->ra_pages, (sb)->s_bdi->io_pages) \ + << (PAGE_SHIFT - sb->s_blocksize_bits)) + /* * helpers for cluster size to byte conversion. */ @@ -117,9 +122,9 @@ enum { #define FAT_ENT_SIZE (4) #define FAT_ENT_SIZE_BITS (2) #define FAT_ENT_OFFSET_SECTOR(sb, loc) (EXFAT_SB(sb)->FAT1_start_sector + \ - (((u64)loc << FAT_ENT_SIZE_BITS) >> sb->s_blocksize_bits)) + (((u64)(loc) << FAT_ENT_SIZE_BITS) >> sb->s_blocksize_bits)) #define FAT_ENT_OFFSET_BYTE_IN_SECTOR(sb, loc) \ - ((loc << FAT_ENT_SIZE_BITS) & (sb->s_blocksize - 1)) + (((loc) << FAT_ENT_SIZE_BITS) & (sb->s_blocksize - 1)) /* * helpers for bitmap. diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c index 71ee16479c43..0c17621587d5 100644 --- a/fs/exfat/fatent.c +++ b/fs/exfat/fatent.c @@ -142,13 +142,51 @@ int exfat_ent_get(struct super_block *sb, unsigned int loc, return -EIO; } +static int exfat_blk_readahead(struct super_block *sb, sector_t sec, + sector_t *ra, blkcnt_t *ra_cnt, sector_t end) +{ + struct blk_plug plug; + + if (sec < *ra) + return 0; + + *ra += *ra_cnt; + + /* No blocks left (or only the last block), skip readahead. */ + if (*ra >= end) + return 0; + + *ra_cnt = min(end - *ra + 1, EXFAT_BLK_RA_SIZE(sb)); + if (*ra_cnt == 0) { + /* Move 'ra' to the end to disable readahead. */ + *ra = end; + return 0; + } + + blk_start_plug(&plug); + for (unsigned int i = 0; i < *ra_cnt; i++) + sb_breadahead(sb, *ra + i); + blk_finish_plug(&plug); + return 0; +} + int exfat_chain_cont_cluster(struct super_block *sb, unsigned int chain, unsigned int len) { + sector_t sec, end, ra; + blkcnt_t ra_cnt; + if (!len) return 0; + ra_cnt = 0; + ra = FAT_ENT_OFFSET_SECTOR(sb, chain); + end = FAT_ENT_OFFSET_SECTOR(sb, chain + len - 1); + while (len > 1) { + sec = FAT_ENT_OFFSET_SECTOR(sb, chain); + exfat_blk_readahead(sb, sec, &ra, &ra_cnt, end); + if (exfat_ent_set(sb, chain, chain + 1)) return -EIO; chain++; -- 2.43.0