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    SubjectRe: [RFC PATCH v3 14/15] dcache: Implement partial shrink via Slab Movable Objects
    On Thu, Apr 11, 2019 at 11:34:40AM +1000, Tobin C. Harding wrote:
    > +/*
    > + * d_isolate() - Dentry isolation callback function.
    > + * @s: The dentry cache.
    > + * @v: Vector of pointers to the objects to isolate.
    > + * @nr: Number of objects in @v.
    > + *
    > + * The slab allocator is holding off frees. We can safely examine
    > + * the object without the danger of it vanishing from under us.
    > + */
    > +static void *d_isolate(struct kmem_cache *s, void **v, int nr)
    > +{
    > + struct dentry *dentry;
    > + int i;
    > +
    > + for (i = 0; i < nr; i++) {
    > + dentry = v[i];
    > + __dget(dentry);
    > + }
    > +
    > + return NULL; /* No need for private data */
    > +}

    Huh? This is compeletely wrong; what you need is collecting the ones
    with zero refcount (and not on shrink lists) into a private list.
    *NOT* bumping the refcounts at all. And do it in your isolate thing.

    > +static void d_partial_shrink(struct kmem_cache *s, void **v, int nr,
    > + int node, void *_unused)
    > +{
    > + struct dentry *dentry;
    > + LIST_HEAD(dispose);
    > + int i;
    > +
    > + for (i = 0; i < nr; i++) {
    > + dentry = v[i];
    > + spin_lock(&dentry->d_lock);
    > + dentry->d_lockref.count--;
    > +
    > + if (dentry->d_lockref.count > 0 ||
    > + dentry->d_flags & DCACHE_SHRINK_LIST) {
    > + spin_unlock(&dentry->d_lock);
    > + continue;
    > + }
    > +
    > + if (dentry->d_flags & DCACHE_LRU_LIST)
    > + d_lru_del(dentry);
    > +
    > + d_shrink_add(dentry, &dispose);
    > +
    > + spin_unlock(&dentry->d_lock);
    > + }

    Basically, that loop (sans jerking the refcount up and down) should
    get moved into d_isolate().
    > +
    > + if (!list_empty(&dispose))
    > + shrink_dentry_list(&dispose);
    > +}

    ... with this left in d_partial_shrink(). And you obviously need some way
    to pass the list from the former to the latter...

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