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    SubjectRe: [PATCH 2/6] lib/rhashtable: guarantee initial hashtable allocation
    On Thu, May 24, 2018 at 02:11:31PM -0700, Davidlohr Bueso wrote:
    >
    > -static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
    > - size_t nbuckets,
    > - gfp_t gfp)
    > +static struct bucket_table *__bucket_table_alloc(struct rhashtable *ht,
    > + size_t nbuckets,
    > + gfp_t gfp, bool retry)
    > {
    > struct bucket_table *tbl = NULL;
    > size_t size, max_locks;
    > int i;
    >
    > size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
    > + if (retry) {
    > + gfp |= __GFP_NOFAIL;
    > + tbl = kzalloc(size, gfp);
    > + } /* fall-through */

    I'd prefer this logic to be moved to the caller. So just call the
    function with GFP_KERNEL | __GFP_NOFAIL.

    Of course you need to modify bucket_table_alloc so that it still
    treats this as GFP_KERNEL (as opposed to GFP_ATOMIC). That is,
    instead of

    > if (gfp != GFP_KERNEL)

    You will need
    if ((gfp & ~__GFP_NOFAIL) != GFP_KERNEL)

    > @@ -1067,9 +1086,20 @@ int rhashtable_init(struct rhashtable *ht,
    > }
    > }
    >
    > + /*
    > + * This is api initialization and thus we need to guarantee the
    > + * initial rhashtable allocation. Upon failure, retry with a
    > + * smallest possible size, otherwise we exhaust our options with
    > + * __GFP_NOFAIL.
    > + */
    > tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
    > - if (tbl == NULL)
    > - return -ENOMEM;
    > + if (unlikely(tbl == NULL)) {
    > + size = HASH_MIN_SIZE;
    > +
    > + tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
    > + if (tbl == NULL)
    > + tbl = bucket_table_alloc_retry(ht, size, GFP_KERNEL);
    > + }

    Perhaps you should also explain here why we don't just try the
    minimum size with __GFP_NOFAIL as the second step rather than the
    third.

    Cheers,
    --
    Email: Herbert Xu <herbert@gondor.apana.org.au>
    Home Page: http://gondor.apana.org.au/~herbert/
    PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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