From patchwork Thu Jul 27 15:20:20 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chengming Zhou X-Patchwork-Id: 13330278 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 993EDC0015E for ; Thu, 27 Jul 2023 15:21:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234561AbjG0PV6 (ORCPT ); Thu, 27 Jul 2023 11:21:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234573AbjG0PVx (ORCPT ); Thu, 27 Jul 2023 11:21:53 -0400 Received: from out-68.mta0.migadu.com (out-68.mta0.migadu.com [IPv6:2001:41d0:1004:224b::44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2145D30E1 for ; Thu, 27 Jul 2023 08:21:46 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1690471303; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MHEGgdVdHj4vY18bdOXyRtJoqYQZlvIgYxDQJPuL59w=; b=Vv/FGX69XOHCDVN28FE8R9XfgBkvYOjRJ9IrvFT4uw+lvzw0cVFHnWmhOhZGe5DGQq4Vm6 xenzswl7kJ31dEbx9wuTzt3TmK2vDnonf0xi2V8MGao8+9SF3mSueeizHrtPzSG04Vm5+Z hNGBLEjRgjptwa72wdpo33hUSoujnnA= From: chengming.zhou@linux.dev To: axboe@kernel.dk, osandov@fb.com, ming.lei@redhat.com, kbusch@kernel.org, krisman@suse.de Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com Subject: [PATCH v2 3/3] sbitmap: drop wrap logic in __sbitmap_get_word() Date: Thu, 27 Jul 2023 23:20:20 +0800 Message-ID: <20230727152020.3633009-3-chengming.zhou@linux.dev> In-Reply-To: <20230727152020.3633009-1-chengming.zhou@linux.dev> References: <20230727152020.3633009-1-chengming.zhou@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org From: Chengming Zhou The complex wrap logic in __sbitmap_get_word() seems unnecessary: 1. Strict round-robin mode: wrap == false 1.1 hint == 0: we search sb->map_nr words, won't wrap 1.2 hint > 0: we search (sb->map_nr + 1) words, won't wrap 2. Non round-robin mode: wrap == true 2.1 hint == 0: we search sb->map_nr words, don't need wrap 2.2 hint > 0: we search sb->map_nr words, need wrap So 2.2 is the only reason we need wrap logic in __sbitmap_get_word(), the only user like 2.2 is __sbitmap_get_shallow(). __sbitmap_get_shallow() always set wrap == true no matter the sbitmap is round-robin or not, seems that it doesn't want strict round-robin tag in this limited case. We can remove 2.2 case by setting hint == 0 in __sbitmap_get_shallow(), since there is no point in looping twice in find_next_zero_bit() if we don't want strict round-robin tag for this case. Signed-off-by: Chengming Zhou --- lib/sbitmap.c | 47 +++++++++++++---------------------------------- 1 file changed, 13 insertions(+), 34 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 6e098a46be26..d042dc5d53c3 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -134,41 +134,21 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth) EXPORT_SYMBOL_GPL(sbitmap_resize); static int __sbitmap_get_word(unsigned long *word, unsigned long depth, - unsigned int hint, bool wrap) + unsigned int hint) { int nr; - /* don't wrap if starting from 0 */ - wrap = wrap && hint; - while (1) { nr = find_next_zero_bit(word, depth, hint); - if (unlikely(nr >= depth)) { - /* - * We started with an offset, and we didn't reset the - * offset to 0 in a failure case, so start from 0 to - * exhaust the map. - */ - if (wrap) { - wrap = false; - hint = 0; - continue; - } + if (unlikely(nr >= depth)) return -1; - } if (!test_and_set_bit_lock(nr, word)) break; hint = nr + 1; - if (unlikely(hint >= depth)) { - if (wrap) { - wrap = false; - hint = 0; - continue; - } + if (unlikely(hint >= depth)) return -1; - } } return nr; @@ -176,14 +156,13 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth, static int sbitmap_find_bit_in_word(struct sbitmap_word *map, unsigned int depth, - unsigned int alloc_hint, - bool wrap) + unsigned int alloc_hint) { int nr; do { nr = __sbitmap_get_word(&map->word, depth, - alloc_hint, wrap); + alloc_hint); if (nr != -1) break; if (!sbitmap_deferred_clear(map)) @@ -196,8 +175,7 @@ static int sbitmap_find_bit_in_word(struct sbitmap_word *map, static int sbitmap_find_bit(struct sbitmap *sb, unsigned int depth, unsigned int index, - unsigned int alloc_hint, - bool wrap) + unsigned int alloc_hint) { unsigned int map_nr = sb->map_nr; unsigned int i; @@ -207,7 +185,7 @@ static int sbitmap_find_bit(struct sbitmap *sb, * If we have alloc_hint > 0 and don't wrap, we need to * recheck sb->map[index] with hint == 0 to exhaust the map. */ - if (alloc_hint && !wrap) + if (alloc_hint) map_nr += 1; for (i = 0; i < map_nr; i++) { @@ -215,7 +193,7 @@ static int sbitmap_find_bit(struct sbitmap *sb, min_t(unsigned int, __map_depth(sb, index), depth), - alloc_hint, wrap); + alloc_hint); if (nr != -1) { nr += index << sb->shift; @@ -247,8 +225,7 @@ static int __sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint) else alloc_hint = 0; - return sbitmap_find_bit(sb, UINT_MAX, index, alloc_hint, - !sb->round_robin); + return sbitmap_find_bit(sb, UINT_MAX, index, alloc_hint); } int sbitmap_get(struct sbitmap *sb) @@ -275,9 +252,11 @@ static int __sbitmap_get_shallow(struct sbitmap *sb, unsigned int index; index = SB_NR_TO_INDEX(sb, alloc_hint); - alloc_hint = SB_NR_TO_BIT(sb, alloc_hint); - return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint, true); + /* No point in looping twice in find_next_zero_bit() for this case. */ + alloc_hint = 0; + + return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint); } int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth)