git: 02ec31bdf60f - main - cache: add back target entry on rename

[Oliver Pinter]

On Saturday, January 23, 2021, Mateusz Guzik <mjg at freebsd.org> wrote:

> The branch main has been updated by mjg:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=
> 02ec31bdf60fa3a8530544cb3c8c4ec1df6cde0d
>
> commit 02ec31bdf60fa3a8530544cb3c8c4ec1df6cde0d
> Author:     Mateusz Guzik <mjg at FreeBSD.org>
> AuthorDate: 2021-01-23 17:21:42 +0000
> Commit:     Mateusz Guzik <mjg at FreeBSD.org>
> CommitDate: 2021-01-23 18:10:16 +0000
>
>     cache: add back target entry on rename
> ---
>  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, "");


 It would be really if the description were filled with proper info.

+
>  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
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