From: Zheng Liang <zhengliang6@xxxxxxxxxx>
Subject: squashfs: provide backing_dev_info in order to disable read-ahead
Commit c1f6925e1091 ("mm: put readahead pages in cache earlier") causes
the read performance of squashfs to deteriorate.Through testing, we find
that the performance will be back by closing the readahead of squashfs.
So we want to learn the way of ubifs, provides backing_dev_info and
disable read-ahead.
--------------------------------------------------------------------
We tested the following data by fio.
squashfs image blocksize=128K
test command:
fio --name basic --bs=? --filename="/mnt/test_file" --rw=? --iodepth=1 --ioengine=psync --runtime=200 --time_based
turn on squashfs readahead in 5.10 kernel
bs(k) read/randread MB/s
4 randread 271
128 randread 231
1024 randread 246
4 read 310
128 read 245
1024 read 247
turn off squashfs readahead in 5.10 kernel
bs(k) read/randread MB/s
4 randread 293
128 randread 330
1024 randread 363
4 read 338
128 read 360
1024 read 365
turn on squashfs readahead and revert the
commit c1f6925e1091("mm: put readahead
pages in cache earlier") in 5.10 kernel
bs(k) read/randread MB/s
4 randread 289
128 randread 306
1024 randread 335
4 read 337
128 read 336
1024 read 338
Link: https://lkml.kernel.org/r/20211116113141.1391026-1-zhengliang6@xxxxxxxxxx
Signed-off-by: Zheng Liang <zhengliang6@xxxxxxxxxx>
Reviewed-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Cc: Zhang Yi <yi.zhang@xxxxxxxxxx>
Cc: Hou Tao <houtao1@xxxxxxxxxx>
Cc: Miao Xie <miaoxie@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/squashfs/super.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
--- a/fs/squashfs/super.c~squashfs-provides-backing_dev_info-in-order-to-disable-read-ahead
+++ a/fs/squashfs/super.c
@@ -29,6 +29,7 @@
#include <linux/module.h>
#include <linux/magic.h>
#include <linux/xattr.h>
+#include <linux/backing-dev.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
@@ -112,6 +113,24 @@ static const struct squashfs_decompresso
return decompressor;
}
+static int squashfs_bdi_init(struct super_block *sb)
+{
+ int err;
+ unsigned int major = MAJOR(sb->s_dev);
+ unsigned int minor = MINOR(sb->s_dev);
+
+ bdi_put(sb->s_bdi);
+ sb->s_bdi = &noop_backing_dev_info;
+
+ err = super_setup_bdi_name(sb, "squashfs_%u_%u", major, minor);
+ if (err)
+ return err;
+
+ sb->s_bdi->ra_pages = 0;
+ sb->s_bdi->io_pages = 0;
+
+ return 0;
+}
static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
@@ -127,6 +146,20 @@ static int squashfs_fill_super(struct su
TRACE("Entered squashfs_fill_superblock\n");
+ /*
+ * squashfs provides 'backing_dev_info' in order to disable read-ahead. For
+ * squashfs, I/O is not deferred, it is done immediately in readpage,
+ * which means the user would always have to wait their own I/O. So the effect
+ * of readahead is very weak for squashfs. squashfs_bdi_init will set
+ * sb->s_bdi->ra_pages and sb->s_bdi->io_pages to 0 and close readahead for
+ * squashfs.
+ */
+ err = squashfs_bdi_init(sb);
+ if (err) {
+ errorf(fc, "squashfs init bdi failed");
+ return err;
+ }
+
sb->s_fs_info = kzalloc(sizeof(*msblk), GFP_KERNEL);
if (sb->s_fs_info == NULL) {
ERROR("Failed to allocate squashfs_sb_info\n");
_
