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

[Mateusz Guzik]

The sysctl at hand is temporary in case someone reports trouble --
then they can flip it. I don't expect it to survive more than a month.

On 1/23/21, Oliver Pinter <oliver.pntr at gmail.com> wrote:
> 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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>


-- 
Mateusz Guzik <mjguzik gmail.com>