From mboxrd@z Thu Jan 1 00:00:00 1970 From: Davidlohr Bueso Subject: [PATCH 2/5] lib/rhashtable: guarantee initial hashtable allocation Date: Fri, 1 Jun 2018 09:01:22 -0700 Message-ID: <20180601160125.30031-3-dave@stgolabs.net> References: <20180601160125.30031-1-dave@stgolabs.net> Return-path: In-Reply-To: <20180601160125.30031-1-dave@stgolabs.net> Sender: linux-kernel-owner@vger.kernel.org To: akpm@linux-foundation.org, torvalds@linux-foundation.org Cc: tgraf@suug.ch, herbert@gondor.apana.org.au, manfred@colorfullife.com, mhocko@kernel.org, guillaume.knispel@supersonicimagine.com, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Davidlohr Bueso , Davidlohr Bueso List-Id: linux-api@vger.kernel.org rhashtable_init() may fail due to -ENOMEM, thus making the entire api unusable. This patch removes this scenario, however unlikely. In order to guarantee memory allocation, this patch always ends up doing GFP_KERNEL|__GFP_NOFAIL for both the tbl as well as alloc_bucket_spinlocks(). Upon the first table allocation failure, we shrink the size to the smallest value that makes sense retry with __GFP_NOFAIL semantics. With the defaults, this means that from 64 buckets, we retry with only 4. Any later issues regarding performance due to collisions or larger table resizing (when more memory becomes available) is the last of our problems. Suggested-by: Linus Torvalds Signed-off-by: Davidlohr Bueso --- lib/rhashtable.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 05a4b1b8b8ce..ae17da6f0c75 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -175,7 +175,7 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht, int i; size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]); - if (gfp != GFP_KERNEL) + if ((gfp & ~__GFP_NOFAIL) != GFP_KERNEL) tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY); else tbl = kvzalloc(size, gfp); @@ -1067,9 +1067,16 @@ int rhashtable_init(struct rhashtable *ht, } } + /* + * This is api initialization and thus we need to guarantee the + * initial rhashtable allocation. Upon failure, retry with the + * smallest possible size with __GFP_NOFAIL semantics. + */ tbl = bucket_table_alloc(ht, size, GFP_KERNEL); - if (tbl == NULL) - return -ENOMEM; + if (unlikely(tbl == NULL)) { + size = min_t(u16, ht->p.min_size, HASH_MIN_SIZE); + tbl = bucket_table_alloc(ht, size, GFP_KERNEL | __GFP_NOFAIL); + } atomic_set(&ht->nelems, 0); -- 2.16.3