From: Robin Dong <sanbai@xxxxxxxxxx>
We found performance regression when using bigalloc with "nodelalloc" (1MB cluster size):
1. mke2fs -C 1048576 -O ^has_journal,bigalloc /dev/sda
2. mount -o nodelalloc /dev/sda /test/
3. time dd if=/dev/zero of=/test/io bs=1048576 count=1024
The "dd" will cost about 2 seconds to finish, but if we mke2fs without "bigalloc",
"dd" will only cost lesss than 1 second.
The reason is: when using ext4 with "nodelalloc", it will call ext4_find_delalloc_cluster() nearly
everytime it call ext4_ext_map_blocks(), and ext4_find_delalloc_cluster() will also scan all pages
in cluster because no buffer is "delayed".
A cluster has 256 pages (1MB cluster), so it will scan 256 * 256k pags when creating a 1G file. That
severely hurts the performance.
Therefore, we don't call ext4_find_delalloc_cluster() when use "nodelalloc".
Signed-off-by: Robin Dong <sanbai@xxxxxxxxxx>
---
fs/ext4/extents.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 61fa9e1..e15d32b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3724,7 +3724,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
if (!(flags & EXT4_GET_BLOCKS_PUNCH_OUT_EXT) &&
ext4_ext_in_cache(inode, map->m_lblk, &newex)) {
if (!newex.ee_start_lo && !newex.ee_start_hi) {
- if ((sbi->s_cluster_ratio > 1) &&
+ if ((flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
+ (sbi->s_cluster_ratio > 1) &&
ext4_find_delalloc_cluster(inode, map->m_lblk, 0))
map->m_flags |= EXT4_MAP_FROM_CLUSTER;
@@ -3900,7 +3901,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
}
}
- if ((sbi->s_cluster_ratio > 1) &&
+ if ((flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
+ (sbi->s_cluster_ratio > 1) &&
ext4_find_delalloc_cluster(inode, map->m_lblk, 0))
map->m_flags |= EXT4_MAP_FROM_CLUSTER;
--
1.7.4.1
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