> -----Original Message-----
> From: Wangkai (Kevin,C)
> Sent: Monday, August 07, 2017 5:55 PM
> To: linux-fsdevel@xxxxxxxxxxxxxxx; viro@xxxxxxxxxxxxxxxxxx
> Cc: Wangkai (Kevin,C); Renjinyong (Renjinyong, Business Support Dept)
> Subject: [PATCH] fs/dcache: dentries should free after files unlinked or
> directories removed
>
> sometimes, on my server, there were lots of files creating and removing, and I
> found that memory usage were high, and I checked, almost all the memory was
> occupied by slab recliamable, the slab struct was dentry, and I checked the
> code of dcache, and found that when a file was deleted the dentry never free,
> unless a memory recliam was triggerd.
>
> I made this patch to mark the dentry as a remove state after file unlinked or
> directory removed, and when the dentry’s reference count dec to zero and
> free it, and it worked well on my server base on kernel 4.4.
>
>
> Signed-off-by: Wangkai <wangkai86@xxxxxxxxxx>
> ---
> fs/dcache.c | 12 +++++++++++-
> fs/namei.c | 6 ++++++
> include/linux/dcache.h | 2 +-
> 3 files changed, 18 insertions(+), 2 deletions(-)
> mode change 100644 => 100755 fs/dcache.c
> mode change 100644 => 100755 fs/namei.c
> mode change 100644 => 100755 include/linux/dcache.h
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> old mode 100644
> new mode 100755
> index f901413..6828463
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -722,7 +722,8 @@ static inline bool fast_dput(struct dentry *dentry)
> */
> smp_rmb();
> d_flags = ACCESS_ONCE(dentry->d_flags);
> - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST |
> DCACHE_DISCONNECTED;
> + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST |
> DCACHE_DISCONNECTED
> + | DCACHE_FILE_REMOVED;
>
> /* Nothing to do? Dropping the reference was all we needed? */
> if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST)
> && !d_unhashed(dentry))
> @@ -816,6 +817,15 @@ void dput(struct dentry *dentry)
> dentry_lru_add(dentry);
>
> dentry->d_lockref.count--;
> +
> + /*
> + * if file has been declare as removed and reference count is zero
> + * then we can free the dentry rather than leave it stay in dcache
> + */
> + if (unlikely(dentry->d_flags & DCACHE_FILE_REMOVED)) {
> + if (dentry->d_lockref.count == 0)
> + goto kill_it;
> + }
> spin_unlock(&dentry->d_lock);
> return;
>
> diff --git a/fs/namei.c b/fs/namei.c
> old mode 100644
> new mode 100755
> index ddb6a7c..0ec1478
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3918,6 +3918,9 @@ static long do_rmdir(int dfd, const char __user
> *pathname)
> goto exit3;
> error = vfs_rmdir(path.dentry->d_inode, dentry);
> exit3:
> + /* after remove the dir set dentry remove flag */
> + if (!error)
> + dentry->d_flags |= DCACHE_FILE_REMOVED;
> dput(dentry);
> exit2:
> inode_unlock(path.dentry->d_inode);
> @@ -4042,6 +4045,9 @@ static long do_unlinkat(int dfd, const char __user
> *pathname)
> goto exit2;
> error = vfs_unlink(path.dentry->d_inode, dentry, &delegated_inode);
> exit2:
> + /* after unlink file set dentry remove flag */
> + if (!error)
> + dentry->d_flags |= DCACHE_FILE_REMOVED;
> dput(dentry);
> }
> inode_unlock(path.dentry->d_inode);
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> old mode 100644
> new mode 100755
> index aae1cdb..2d65bd6
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -215,7 +215,7 @@ struct dentry_operations {
> #define DCACHE_FALLTHRU 0x01000000 /* Fall through to lower
> layer */
> #define DCACHE_ENCRYPTED_WITH_KEY 0x02000000 /* dir is encrypted
> with a valid key */
> #define DCACHE_OP_REAL 0x04000000
> -
> +#define DCACHE_FILE_REMOVED 0x08000000 /* file or dir has been
> unlinked or removed */
> #define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with
> parent locked shared) */
> #define DCACHE_DENTRY_CURSOR 0x20000000
>
> --
> 2.8.0.GIT
Hi, all
The negative dentries keep growing and waste a lots of kernel memory, this problem has been
Occurred on my server, and I looked for internet, and many people had met the same problem.
Recently, I discussed with Longman, we have two different patches to solve this problem,
In my patch, remove the negative dentries with the files unlinked, I checked 15 years ago,
Viro and linus had talked about this, that unlink was only worth doing.
ref: http://yarchive.net/comp/linux/negative_dentries.html
in Longman patch, limit the negative dentries number
maybe we can discuss.
Thanks,
Kevin
