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ext4: limit the length of per-inode prealloc list

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In the scenario of writing sparse files, the per-inode prealloc list may
be very long, resulting in high overhead for ext4_mb_use_preallocated().
To circumvent this problem, we limit the maximum length of per-inode
prealloc list to 512 and allow users to modify it.

After patching, we observed that the sys ratio of cpu has dropped, and
the system throughput has increased significantly. We created a process
to write the sparse file, and the running time of the process on the
fixed kernel was significantly reduced, as follows:

Running time on unfixed kernel：
[root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
real    0m2.051s
user    0m0.008s
sys     0m2.026s

Running time on fixed kernel：
[root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
real    0m0.471s
user    0m0.004s
sys     0m0.395s

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Link: https://lore.kernel.org/r/d7a98178-056b-6db5-6bce-4ead23f4a257@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
brookxu
2020-08-17 15:36:15 +08:00
committed by Theodore Ts'o
parent 66d5e0277e
commit 27bc446e2d
13 changed files with 104 additions and 29 deletions
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6
fs/ext4/inode.c
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@@ -383,7 +383,7 @@ void ext4_da_update_reserve_space(struct inode *inode,
*/
if ((ei->i_reserved_data_blocks == 0) &&
!inode_is_open_for_write(inode))
ext4_discard_preallocations(inode);
ext4_discard_preallocations(inode, 0);
}
static int __check_block_validity(struct inode *inode, const char *func,
@@ -4055,7 +4055,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
if (stop_block > first_block) {
down_write(&EXT4_I(inode)->i_data_sem);
ext4_discard_preallocations(inode);
ext4_discard_preallocations(inode, 0);
ret = ext4_es_remove_extent(inode, first_block,
stop_block - first_block);
@@ -4210,7 +4210,7 @@ int ext4_truncate(struct inode *inode)
down_write(&EXT4_I(inode)->i_data_sem);
ext4_discard_preallocations(inode);
ext4_discard_preallocations(inode, 0);
if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
err = ext4_ext_truncate(handle, inode);