Re: [PATCH] ext4: Remove expensive flush on fast commit
From: Andreas Dilger <hidden>
Date: 2021-01-08 02:27:12
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On Tue, Jan 5, 2021 at 5:32 PM Daejun Park [off-list ref] wrote:
In the fast commit, it adds REQ_FUA and REQ_PREFLUSH on each fast commit block when barrier is enabled. However, in recovery phase, ext4 compares CRC value in the tail. So it is sufficient adds REQ_FUA and REQ_PREFLUSH on the block that has tail.
Does the tail block *always* contain a CRC, or is that dependent on EXT4_FEATURE_RO_COMPAT_METADATA_CSUM, JBD2_FEATURE_INCOMPAT_CSUM_V2, or JBD2_FEATURE_INCOMPAT_CSUM_V3 being enabled? If one of those features is *required* before the FAST_COMMIT feature can be used, then this patch looks OK. Otherwise, the CSUM feature should be checked before the FUA is skipped for non-tail blocks. Cheers, Andreas
quoted hunk ↗ jump to hunk
Signed-off-by: Daejun Park <redacted> --- fs/ext4/fast_commit.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c index 4fcc21c25e79..e66507be334c 100644 --- a/fs/ext4/fast_commit.c +++ b/fs/ext4/fast_commit.c@@ -604,13 +604,13 @@ void ext4_fc_track_range(handle_t *handle, struct inode *inode, ext4_lblk_t star trace_ext4_fc_track_range(inode, start, end, ret);} -static void ext4_fc_submit_bh(struct super_block *sb) +static void ext4_fc_submit_bh(struct super_block *sb, bool is_tail) { int write_flags = REQ_SYNC; struct buffer_head *bh = EXT4_SB(sb)->s_fc_bh; - /* TODO: REQ_FUA | REQ_PREFLUSH is unnecessarily expensive. */ - if (test_opt(sb, BARRIER)) + /* Add REQ_FUA | REQ_PREFLUSH only its tail */ + if (test_opt(sb, BARRIER) && is_tail) write_flags |= REQ_FUA | REQ_PREFLUSH; lock_buffer(bh); set_buffer_dirty(bh);@@ -684,7 +684,7 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc) *crc = ext4_chksum(sbi, *crc, tl, sizeof(*tl)); if (pad_len > 0) ext4_fc_memzero(sb, tl + 1, pad_len, crc); - ext4_fc_submit_bh(sb); + ext4_fc_submit_bh(sb, false); ret = jbd2_fc_get_buf(EXT4_SB(sb)->s_journal, &bh); if (ret)@@ -741,7 +741,7 @@ static int ext4_fc_write_tail(struct super_block *sb, u32 crc) tail.fc_crc = cpu_to_le32(crc); ext4_fc_memcpy(sb, dst, &tail.fc_crc, sizeof(tail.fc_crc), NULL); - ext4_fc_submit_bh(sb); + ext4_fc_submit_bh(sb, true); return 0;} -- 2.25.1
Cheers, Andreas
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