From patchwork Thu Sep 16 15:58:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 513744 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C7C3C433EF for ; Thu, 16 Sep 2021 17:19:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6DFD61108 for ; Thu, 16 Sep 2021 17:19:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243446AbhIPRVF (ORCPT ); Thu, 16 Sep 2021 13:21:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:43508 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350881AbhIPRSA (ORCPT ); Thu, 16 Sep 2021 13:18:00 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 372E261423; Thu, 16 Sep 2021 16:40:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631810444; bh=3QzOoWllqrVwAdmoOqhylwbj530Jk04mhqnaBOffYo8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nd0oPe0/oygwtB065DjZLDVRrHd7Zb8XdK3P9SZhoolqOejG0aHHg3DEgKQZJeQav Hx2o0OZ93Xct70bjS08bFhdjHEhVbX7c0rLeaIBQCakNGEhdgxwF0we2qAaiJb7WcU Sl4S/CCjCiFhel5y84rWyTR1PItUXAVxXefV6eU0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Howells , Jeff Layton , linux-cachefs@redhat.com, Sasha Levin Subject: [PATCH 5.14 144/432] fscache: Fix cookie key hashing Date: Thu, 16 Sep 2021 17:58:13 +0200 Message-Id: <20210916155815.643366765@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210916155810.813340753@linuxfoundation.org> References: <20210916155810.813340753@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: David Howells [ Upstream commit 35b72573e977ed6b18b094136a4fa3e0ffb13603 ] The current hash algorithm used for hashing cookie keys is really bad, producing almost no dispersion (after a test kernel build, ~30000 files were split over just 18 out of the 32768 hash buckets). Borrow the full_name_hash() hash function into fscache to do the hashing for cookie keys and, in the future, volume keys. I don't want to use full_name_hash() as-is because I want the hash value to be consistent across arches and over time as the hash value produced may get used on disk. I can also optimise parts of it away as the key will always be a padded array of aligned 32-bit words. Fixes: ec0328e46d6e ("fscache: Maintain a catalogue of allocated cookies") Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/162431201844.2908479.8293647220901514696.stgit@warthog.procyon.org.uk/ Signed-off-by: Sasha Levin --- fs/fscache/cookie.c | 14 +------------- fs/fscache/internal.h | 2 ++ fs/fscache/main.c | 39 +++++++++++++++++++++++++++++++++++++++ 3 files changed, 42 insertions(+), 13 deletions(-) diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c index 751bc5b1cddf..6104f627cc71 100644 --- a/fs/fscache/cookie.c +++ b/fs/fscache/cookie.c @@ -74,10 +74,8 @@ void fscache_free_cookie(struct fscache_cookie *cookie) static int fscache_set_key(struct fscache_cookie *cookie, const void *index_key, size_t index_key_len) { - unsigned long long h; u32 *buf; int bufs; - int i; bufs = DIV_ROUND_UP(index_key_len, sizeof(*buf)); @@ -91,17 +89,7 @@ static int fscache_set_key(struct fscache_cookie *cookie, } memcpy(buf, index_key, index_key_len); - - /* Calculate a hash and combine this with the length in the first word - * or first half word - */ - h = (unsigned long)cookie->parent; - h += index_key_len + cookie->type; - - for (i = 0; i < bufs; i++) - h += buf[i]; - - cookie->key_hash = h ^ (h >> 32); + cookie->key_hash = fscache_hash(0, buf, bufs); return 0; } diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h index c483863b740a..aee639d980ba 100644 --- a/fs/fscache/internal.h +++ b/fs/fscache/internal.h @@ -97,6 +97,8 @@ extern struct workqueue_struct *fscache_object_wq; extern struct workqueue_struct *fscache_op_wq; DECLARE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait); +extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n); + static inline bool fscache_object_congested(void) { return workqueue_congested(WORK_CPU_UNBOUND, fscache_object_wq); diff --git a/fs/fscache/main.c b/fs/fscache/main.c index c1e6cc9091aa..4207f98e405f 100644 --- a/fs/fscache/main.c +++ b/fs/fscache/main.c @@ -93,6 +93,45 @@ static struct ctl_table fscache_sysctls_root[] = { }; #endif +/* + * Mixing scores (in bits) for (7,20): + * Input delta: 1-bit 2-bit + * 1 round: 330.3 9201.6 + * 2 rounds: 1246.4 25475.4 + * 3 rounds: 1907.1 31295.1 + * 4 rounds: 2042.3 31718.6 + * Perfect: 2048 31744 + * (32*64) (32*31/2 * 64) + */ +#define HASH_MIX(x, y, a) \ + ( x ^= (a), \ + y ^= x, x = rol32(x, 7),\ + x += y, y = rol32(y,20),\ + y *= 9 ) + +static inline unsigned int fold_hash(unsigned long x, unsigned long y) +{ + /* Use arch-optimized multiply if one exists */ + return __hash_32(y ^ __hash_32(x)); +} + +/* + * Generate a hash. This is derived from full_name_hash(), but we want to be + * sure it is arch independent and that it doesn't change as bits of the + * computed hash value might appear on disk. The caller also guarantees that + * the hashed data will be a series of aligned 32-bit words. + */ +unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n) +{ + unsigned int a, x = 0, y = salt; + + for (; n; n--) { + a = *data++; + HASH_MIX(x, y, a); + } + return fold_hash(x, y); +} + /* * initialise the fs caching module */