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ceph: make seeky readdir more efficient

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Current cephfs client uses string to indicate start position of
readdir. The string is last entry of previous readdir reply.
This approach does not work for seeky readdir because we can
not easily convert the new postion to a string. For seeky readdir,
mds needs to return dentries from the beginning. Client keeps
retrying if the reply does not contain the dentry it wants.

In current version of ceph, mds sorts CDentry in its cache in
hash order. Client also uses dentry hash to compose dir postion.
For seeky readdir, if client passes the hash part of dir postion
to mds. mds can avoid replying useless dentries.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Yan, Zheng
2017-04-05 12:54:05 -04:00
committed by Ilya Dryomov
parent 2827528da0
commit 79162547b7
5 changed files with 21 additions and 6 deletions
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17
fs/ceph/inode.c
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@@ -1482,10 +1482,17 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
if (test_bit(CEPH_MDS_R_ABORTED, &req->r_req_flags))
return readdir_prepopulate_inodes_only(req, session);
if (rinfo->hash_order && req->r_path2) {
last_hash = ceph_str_hash(ci->i_dir_layout.dl_dir_hash,
req->r_path2, strlen(req->r_path2));
last_hash = ceph_frag_value(last_hash);
if (rinfo->hash_order) {
if (req->r_path2) {
last_hash = ceph_str_hash(ci->i_dir_layout.dl_dir_hash,
req->r_path2,
strlen(req->r_path2));
last_hash = ceph_frag_value(last_hash);
} else if (rinfo->offset_hash) {
/* mds understands offset_hash */
WARN_ON_ONCE(req->r_readdir_offset != 2);
last_hash = le32_to_cpu(rhead->args.readdir.offset_hash);
}
}
if (rinfo->dir_dir &&
@@ -1510,7 +1517,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
}
if (ceph_frag_is_leftmost(frag) && req->r_readdir_offset == 2 &&
!(rinfo->hash_order && req->r_path2)) {
!(rinfo->hash_order && last_hash)) {
/* note dir version at start of readdir so we can tell
* if any dentries get dropped */
req->r_dir_release_cnt = atomic64_read(&ci->i_release_count);