Btrfs: add readahead for send_write
Btrfs send reads data from disk and then writes to a stream via pipe or
a file via flush.
Currently we're going to read each page a time, so every page results
in a disk read, which is not friendly to disks, esp. HDD. Given that,
the performance can be gained by adding readahead for those pages.
Here is a quick test:
$ btrfs subvolume create send
$ xfs_io -f -c "pwrite 0 1G" send/foobar
$ btrfs subvolume snap -r send ro
$ time "btrfs send ro -f /dev/null"
w/o w
real 1m37.527s 0m9.097s
user 0m0.122s 0m0.086s
sys 0m53.191s 0m12.857s
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 112eb64..6463691 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -124,6 +124,8 @@
struct list_head name_cache_list;
int name_cache_size;
+ struct file_ra_state ra;
+
char *read_buf;
/*
@@ -4170,6 +4172,13 @@
goto out;
last_index = (offset + len - 1) >> PAGE_CACHE_SHIFT;
+
+ /* initial readahead */
+ memset(&sctx->ra, 0, sizeof(struct file_ra_state));
+ file_ra_state_init(&sctx->ra, inode->i_mapping);
+ btrfs_force_ra(inode->i_mapping, &sctx->ra, NULL, index,
+ last_index - index + 1);
+
while (index <= last_index) {
unsigned cur_len = min_t(unsigned, len,
PAGE_CACHE_SIZE - pg_offset);