From patchwork Thu Dec 9 16:54:47 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 12667173 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58BD9C433EF for ; Thu, 9 Dec 2021 16:55:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241617AbhLIQ6p (ORCPT ); Thu, 9 Dec 2021 11:58:45 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:41509 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241625AbhLIQ6c (ORCPT ); Thu, 9 Dec 2021 11:58:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639068898; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=txiUwFn6LAU9WLX8nAEhd/3eVdsKrcCT/qigEzpFoBU=; b=E1yrr3hcQrssOa0ilhE5nRcieP6SZQbI6+dbARrHbGayTcNqx9CozYOvEpf1SnEi4kf6fP wE4v1M/YfMzgNbGWoUFC+psE1VTHjvVYNGCfW3wfASMJaAlYFZxfHke/M+sZfVNKtFtOIN arIcDVXA0HoJY/WT5SPXiw36DJt9FHE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-72-KYhtqsjfPZC3bzPLw8PaoQ-1; Thu, 09 Dec 2021 11:54:53 -0500 X-MC-Unique: KYhtqsjfPZC3bzPLw8PaoQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6A88839382; Thu, 9 Dec 2021 16:54:51 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.122]) by smtp.corp.redhat.com (Postfix) with ESMTP id 340EF60BF1; Thu, 9 Dec 2021 16:54:48 +0000 (UTC) Organization: Red Hat UK Ltd. 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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH v2 07/67] fscache: Implement a hash function From: David Howells To: linux-cachefs@redhat.com Cc: dhowells@redhat.com, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , Matthew Wilcox , Alexander Viro , Omar Sandoval , JeffleXu , Linus Torvalds , linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 09 Dec 2021 16:54:47 +0000 Message-ID: <163906888735.143852.10944614318596881429.stgit@warthog.procyon.org.uk> In-Reply-To: <163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk> References: <163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Implement a function to generate hashes. It needs to be stable over time and endianness-independent as the hashes will appear on disk in future patches. It can assume that its input is a multiple of four bytes in size and alignment. This is borrowed from the VFS and simplified. Signed-off-by: David Howells cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819586113.215744.1699465806130102367.stgit@warthog.procyon.org.uk/ # v1 --- fs/fscache/internal.h | 2 ++ fs/fscache/main.c | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h index ea52f8594a77..64767992bd15 100644 --- a/fs/fscache/internal.h +++ b/fs/fscache/internal.h @@ -22,6 +22,8 @@ */ extern unsigned fscache_debug; +extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n); + /* * proc.c */ diff --git a/fs/fscache/main.c b/fs/fscache/main.c index 819de2ee1276..a4afba1b9d3b 100644 --- a/fs/fscache/main.c +++ b/fs/fscache/main.c @@ -24,6 +24,45 @@ MODULE_PARM_DESC(fscache_debug, struct workqueue_struct *fscache_wq; EXPORT_SYMBOL(fscache_wq); +/* + * 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 */