From mboxrd@z Thu Jan 1 00:00:00 1970 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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 8C3ADC49ED7 for ; Fri, 13 Sep 2019 13:41:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 65B4F2084F for ; Fri, 13 Sep 2019 13:41:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389846AbfIMNl1 (ORCPT ); Fri, 13 Sep 2019 09:41:27 -0400 Received: from mail.ispras.ru ([83.149.199.45]:32892 "EHLO mail.ispras.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388927AbfIMNl1 (ORCPT ); Fri, 13 Sep 2019 09:41:27 -0400 Received: from mail.ispras.ru (localhost [127.0.0.1]) by mail.ispras.ru (Postfix) with ESMTPSA id 9EB1654008B; Fri, 13 Sep 2019 16:41:24 +0300 (MSK) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Fri, 13 Sep 2019 16:41:24 +0300 From: efremov To: Denis Efremov Cc: Matthew Wilcox , akpm@linux-foundation.org, Akinobu Mita , Jan Kara , linux-kernel@vger.kernel.org, Matthew Wilcox , dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-media@vger.kernel.org, Erdem Tumurov , Vladimir Shelekhov Subject: Re: [PATCH v2] lib/memweight.c: open codes bitmap_weight() Organization: ISPRAS In-Reply-To: <85d9e45a-9631-a139-2d65-86a6753a35e6@ispras.ru> References: <20190821074200.2203-1-efremov@ispras.ru> <20190824100102.1167-1-efremov@ispras.ru> <20190825061158.GC28002@bombadil.infradead.org> <20190826183956.GF15933@bombadil.infradead.org> <85d9e45a-9631-a139-2d65-86a6753a35e6@ispras.ru> Message-ID: X-Sender: efremov@ispras.ru User-Agent: Roundcube Webmail/1.1.2 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Sorry, no question, pointer alignment of course. Denis Efremov писал 2019-09-13 14:48: > Hi, > > Sorry for reviving this conversation, but it looks to me like > this function could be reduced to a single bitmap_weight call: > > static inline size_t memweight(const void *ptr, size_t bytes) > { > BUG_ON(bytes >= UINT_MAX / BITS_PER_BYTE); > return bitmap_weight(ptr, bytes * BITS_PER_BYTE); > } > > Comparing to the current implementation > https://elixir.bootlin.com/linux/latest/source/lib/memweight.c#L11 > this results in a signification simplification. > > __bitmap_weight already count last bits with hweight_long as we > discussed earlier. > > int __bitmap_weight(const unsigned long *bitmap, unsigned int bits) > { > ... > if (bits % BITS_PER_LONG) > w += hweight_long(bitmap[k] & BITMAP_LAST_WORD_MASK(bits)); > ... > } > > and __arch_hweight* functions use popcnt instruction. > > I've briefly tested the equivalence of 2 implementations on x86_64 with > fuzzing here: > https://gist.github.com/evdenis/95a8b9b8041e09368b31c3a9510491a5 > > What do you think making this function static inline and moving it > to include/linux/string.h? I could prepare a patch for it and add some > tests for > memweight and bitmap_weight. Or maybe I miss something again? > > Best regards, > Denis