On Fri, Sep 13, 2024 at 4:32 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> Commit 681ce8623567 ("vfs: Delete the associated dentry when deleting a
> file") introduced an unconditional deletion of the associated dentry when a
> file is removed. However, this led to performance regressions in specific
> benchmarks, such as ilebench.sum_operations/s [0], prompting a revert in
> commit 4a4be1ad3a6e ("Revert "vfs: Delete the associated dentry when
> deleting a file"").
>
> This patch seeks to reintroduce the concept conditionally, where the
> associated dentry is deleted only when the user explicitly opts for it
> during file removal. A new sysctl fs.automated_deletion_of_dentry is
> added for this purpose. Its default value is set to 0.
>
> There are practical use cases for this proactive dentry reclamation.
> Besides the Elasticsearch use case mentioned in commit 681ce8623567,
> additional examples have surfaced in our production environment. For
> instance, in video rendering services that continuously generate temporary
> files, upload them to persistent storage servers, and then delete them, a
> large number of negative dentries—serving no useful purpose—accumulate.
> Users in such cases would benefit from proactively reclaiming these
> negative dentries.
>
> Link: https://lore.kernel.org/linux-fsdevel/202405291318.4dfbb352-oliver.sang@xxxxxxxxx [0]
> Link: https://lore.kernel.org/all/20240912-programm-umgibt-a1145fa73bb6@brauner/
> Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
> ---
> fs/dcache.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 3d8daaecb6d1..ffd2cae2ba8d 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -130,6 +130,7 @@ struct dentry_stat_t {
> static DEFINE_PER_CPU(long, nr_dentry);
> static DEFINE_PER_CPU(long, nr_dentry_unused);
> static DEFINE_PER_CPU(long, nr_dentry_negative);
> +static int automated_deletion_of_dentry;
>
> #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
> /* Statistics gathering. */
> @@ -194,6 +195,15 @@ static struct ctl_table fs_dcache_sysctls[] = {
> .mode = 0444,
> .proc_handler = proc_nr_dentry,
> },
> + {
> + .procname = "automated_deletion_of_dentry",
> + .data = &automated_deletion_of_dentry,
> + .maxlen = sizeof(automated_deletion_of_dentry),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = SYSCTL_ONE,
> + },
> };
>
> static int __init init_fs_dcache_sysctls(void)
> @@ -2394,6 +2404,8 @@ void d_delete(struct dentry * dentry)
> * Are we the only user?
> */
> if (dentry->d_lockref.count == 1) {
> + if (automated_deletion_of_dentry)
> + __d_drop(dentry);
> dentry->d_flags &= ~DCACHE_CANT_MOUNT;
> dentry_unlink_inode(dentry);
> } else {
> --
> 2.43.5
>
Gently ping. Any feedback on this change?
--
Regards
Yafang
