git: ba0689009b71 - stable/13 - cache: add back target entry on rename

[Mateusz Guzik]

The branch stable/13 has been updated by mjg:

URL: https://cgit.FreeBSD.org/src/commit/?id=ba0689009b712c558f4ec2b28202a4e45c5bab91

commit ba0689009b712c558f4ec2b28202a4e45c5bab91
Author:     Mateusz Guzik <mjg at FreeBSD.org>
AuthorDate: 2021-01-23 17:21:42 +0000
Commit:     Mateusz Guzik <mjg at FreeBSD.org>
CommitDate: 2021-02-01 12:39:15 +0000

    cache: add back target entry on rename
    
    (cherry picked from commit 02ec31bdf60fa3a8530544cb3c8c4ec1df6cde0d)
---
 sys/kern/vfs_cache.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 770c8ebf061b..03bafc75acaa 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -367,6 +367,10 @@ static bool __read_frequently cache_fast_revlookup = true;
 SYSCTL_BOOL(_vfs, OID_AUTO, cache_fast_revlookup, CTLFLAG_RW,
     &cache_fast_revlookup, 0, "");
 
+static bool __read_mostly cache_rename_add = true;
+SYSCTL_BOOL(_vfs, OID_AUTO, cache_rename_add, CTLFLAG_RW,
+    &cache_rename_add, 0, "");
+
 static u_int __exclusive_cache_line neg_cycle;
 
 #define ncneghash	3
@@ -2731,6 +2735,21 @@ cache_vop_rename(struct vnode *fdvp, struct vnode *fvp, struct vnode *tdvp,
 	} else {
 		cache_remove_cnp(tdvp, tcnp);
 	}
+
+	/*
+	 * TODO
+	 *
+	 * Historically renaming was always purging all revelang entries,
+	 * but that's quite wasteful. In particular turns out that in many cases
+	 * the target file is immediately accessed after rename, inducing a cache
+	 * miss.
+	 *
+	 * Recode this to reduce relocking and reuse the existing entry (if any)
+	 * instead of just removing it above and allocating a new one here.
+	 */
+	if (cache_rename_add) {
+		cache_enter(tdvp, fvp, tcnp);
+	}
 }
 
 void