[Ocfs2-devel] [PATCH] Track negative dentries
Sunil Mushran
sunil.mushran at oracle.com
Fri Jun 18 09:06:00 PDT 2010
Thanks for taking on this task.
One overall comment about comments. Instead of sprinkling
the same line everywhere, add the full description in one place.
Maybe atop ocfs2_attach_dentry_gen(). Describe it fully. And then
let the code speak for itself.
Also, do remember to run the patch thru scripts/checkpatch.pl.
On 06/18/2010 08:02 AM, Goldwyn Rodrigues wrote:
> Track negative dentries by recording the generation number of the parent
> directory in d_fsdata. The generation number for the parent directory is
> recorded in the inode_info, which increments every time the lock on the
> directory is dropped.
>
> If the generation number of the parent directory and the negative dentry
> matches, there is no need to perform the revalidate, else a revalidate
> is forced. This improves performance in situations where nodes look for
> the same non-existent file multiple times.
>
> Thanks Mark for explaining the DLM sequence.
>
> Signed-off-by: Goldwyn Rodrigues<rgoldwyn at suse.de>
> ---
> diff --git a/fs/ocfs2/dcache.c b/fs/ocfs2/dcache.c
> index b4957c7..f29095b 100644
> --- a/fs/ocfs2/dcache.c
> +++ b/fs/ocfs2/dcache.c
> @@ -40,6 +40,16 @@
> #include "inode.h"
> #include "super.h"
>
> +void ocfs2_dentry_attach_gen(struct dentry *dentry)
> +{
> + int *gen = (int *)kmalloc(sizeof(int), GFP_KERNEL);
> + *gen = OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
> + /* Generation numbers are specifically for negative dentries */
> + if (dentry->d_inode)
> + BUG();
> + dentry->d_fsdata = (void *)gen;
> +}
> +
>
kmalloc()s can fail. If this is just an int, why not just store it
directly in d_fsdata. Add appropriate casts.
Also, are you sure about the locking when reading the parent's
generation.
> static int ocfs2_dentry_revalidate(struct dentry *dentry,
> struct nameidata *nd)
> @@ -51,10 +61,21 @@ static int ocfs2_dentry_revalidate(struct dentry *dentry,
> mlog_entry("(0x%p, '%.*s')\n", dentry,
> dentry->d_name.len, dentry->d_name.name);
>
> - /* Never trust a negative dentry - force a new lookup. */
> + /* For a negative dentry -
> + check the generation number of the parent and compare with the
> + one stored in the inode.
> + */
> if (inode == NULL) {
> - mlog(0, "negative dentry: %.*s\n", dentry->d_name.len,
> - dentry->d_name.name);
> + int *gen = (int *)dentry->d_fsdata;
> + int parent_gen =
> + OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
> + mlog(0, "negative dentry: %.*s parent gen: %u dentry gen: %u\n",
> + dentry->d_name.len, dentry->d_name.name,
> + parent_gen, *gen);
> + if (*gen == parent_gen)
> + ret = 1;
> + else
> + *gen = parent_gen;
> goto bail;
> }
>
Code is hard to read. See one possible rewrite below. This rewrite
requires adding a "revalidated" label above ret = 1.
+ int *gen = (int *)dentry->d_fsdata;
+ int pgen = OCFS2_I(dentry->d_parent->d_inode)->ip_generation;
+
+ mlog(0, "negative dentry: %.*s parent gen: %u dentry gen: %u\n",
+ dentry->d_name.len, dentry->d_name.name,
+ parent_gen, *gen);
+
+ if (*gen != pgen) {
+ *gen = pgen;
+ goto bail;
+ }
+
+ goto revalidated;
}
> @@ -227,6 +248,13 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
> if (!inode)
> return 0;
>
> + if (!dentry->d_inode&& dentry->d_fsdata) {
> + /* Converting a negative dentry to positive
> + Clear dentry->d_fsdata */
> + kfree(dentry->d_fsdata);
> + dentry->d_fsdata = dl = NULL;
> + }
> +
>
> if (dl) {
> mlog_bug_on_msg(dl->dl_parent_blkno != parent_blkno,
> " \"%.*s\": old parent: %llu, new: %llu\n",
> @@ -451,6 +479,8 @@ static void ocfs2_dentry_iput(struct dentry
> *dentry, struct inode *inode)
> ocfs2_dentry_lock_put(OCFS2_SB(dentry->d_sb), dl);
>
> out:
> + /* Attach generation number to dentry */
> + ocfs2_dentry_attach_gen(dentry);
> iput(inode);
> }
>
Remove comment. Code is clear.
> @@ -500,7 +530,15 @@ out_move:
> d_move(dentry, target);
> }
>
> +static void ocfs2_dentry_release(struct dentry *dentry)
> +{
> + /* Free the generation number stored in negative dentry */
> + if (!dentry->d_inode&& dentry->d_fsdata)
> + kfree(dentry->d_fsdata);
> +}
>
Shouldn't you be setting d_fsdata to NULL.
> +
> const struct dentry_operations ocfs2_dentry_ops = {
> .d_revalidate = ocfs2_dentry_revalidate,
> .d_iput = ocfs2_dentry_iput,
> + .d_release = ocfs2_dentry_release,
> };
> diff --git a/fs/ocfs2/dcache.h b/fs/ocfs2/dcache.h
> index f5dd178..b79eff7 100644
> --- a/fs/ocfs2/dcache.h
> +++ b/fs/ocfs2/dcache.h
> @@ -64,5 +64,6 @@ void ocfs2_dentry_move(struct dentry *dentry, struct
> dentry *target,
> struct inode *old_dir, struct inode *new_dir);
>
> extern spinlock_t dentry_attach_lock;
> +void ocfs2_dentry_attach_gen(struct dentry *dentry);
>
> #endif /* OCFS2_DCACHE_H */
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 39eb16a..d5fb79b 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -2565,7 +2565,6 @@ void ocfs2_inode_unlock(struct inode *inode,
> if (!ocfs2_is_hard_readonly(OCFS2_SB(inode->i_sb))&&
> !ocfs2_mount_local(osb))
> ocfs2_cluster_unlock(OCFS2_SB(inode->i_sb), lockres, level);
> -
> mlog_exit_void();
> }
>
??
> @@ -3635,10 +3634,18 @@ static int ocfs2_data_convert_worker(struct
> ocfs2_lock_res *lockres,
> {
> struct inode *inode;
> struct address_space *mapping;
> + struct ocfs2_inode_info *oi;
>
> inode = ocfs2_lock_res_inode(lockres);
> mapping = inode->i_mapping;
>
> + if (S_ISDIR(inode->i_mode)) {
> + oi = OCFS2_I(inode);
> + oi->ip_generation++;
> + mlog(0, "generation: %u\n", oi->ip_generation);
> + goto out;
> + }
> +
> if (!S_ISREG(inode->i_mode))
> goto out;
>
> diff --git a/fs/ocfs2/inode.h b/fs/ocfs2/inode.h
> index 9f5f5fc..529729c 100644
> --- a/fs/ocfs2/inode.h
> +++ b/fs/ocfs2/inode.h
> @@ -70,6 +70,8 @@ struct ocfs2_inode_info
> /* Only valid if the inode is the dir. */
> u32 ip_last_used_slot;
> u64 ip_last_used_group;
> + /* Generation number for negative inodes */
> + u32 ip_generation;
>
> struct ocfs2_alloc_reservation ip_la_data_resv;
> };
>
Move the comment to the right. The comment above holds valid
for this field too.
> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> index f171b51..c06753a 100644
> --- a/fs/ocfs2/namei.c
> +++ b/fs/ocfs2/namei.c
> @@ -172,6 +172,8 @@ bail_add:
> goto bail_unlock;
> }
> }
> + else /* Attach generation number for negative dentry */
> + ocfs2_dentry_attach_gen(dentry);
>
Remove comment. Code is clear. Also, else needs to be in the same
line as }.
> bail_unlock:
> /* Don't drop the cluster lock until *after* the d_add --
>
>
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