From patchwork Fri Sep 15 18:37:05 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 13387415 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 1DD99EED629 for ; Fri, 15 Sep 2023 18:38:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236551AbjIOShr (ORCPT ); Fri, 15 Sep 2023 14:37:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236593AbjIOShY (ORCPT ); Fri, 15 Sep 2023 14:37:24 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D42151A5; Fri, 15 Sep 2023 11:37:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To: Content-Type:Content-ID:Content-Description; bh=3Pka9W0lBex+AQwPauK3FVj6595pxpOZ2H5fxz/mNAA=; b=dFE/BuzQ/4dk84AB1Iba3+XdrC JXMu/iEd34lZucm5IbEtzAh+uiXBzC6JWIWXJ6L7G0viTTqwusion1sIbrNWTucYQR93SKyF/Zplk 9ahMcug8JjkZUPz4oWGKulmYYR/++Y385/j2XFDUIPdup9V4Z15DB41Yg2t3NuIfP7KsQttats7Uf BTf4Hpf7CqATNEDHv1XhExUH5g3e0/knqGKLDjxfObp04SXaNypzCk5zeSr3WHLluqDpuJylaIadD O7R+3Y3zcxD3M5re5XX7GAOJy7py560s5Kow44PupHQ/cHTyaIw+bxxmbsRClEkRGDt8tHkwSaLr/ Nmqa0TOw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qhDgk-00BMJ2-9B; Fri, 15 Sep 2023 18:37:10 +0000 From: "Matthew Wilcox (Oracle)" To: linux-kernel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, torvalds@linux-foundation.org, Nicholas Piggin Subject: [PATCH 15/17] mm: Add folio_xor_flags_has_waiters() Date: Fri, 15 Sep 2023 19:37:05 +0100 Message-Id: <20230915183707.2707298-16-willy@infradead.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20230915183707.2707298-1-willy@infradead.org> References: <20230915183707.2707298-1-willy@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Optimise folio_end_read() by setting the uptodate bit at the same time we clear the unlock bit. This saves at least one memory barrier and one write-after-write hazard. Signed-off-by: Matthew Wilcox (Oracle) --- include/linux/page-flags.h | 19 +++++++++++++++++++ mm/filemap.c | 14 +++++++++++--- 2 files changed, 30 insertions(+), 3 deletions(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 5c02720c53a5..a88e64acebfe 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -692,6 +692,25 @@ TESTPAGEFLAG_FALSE(Ksm, ksm) u64 stable_page_flags(struct page *page); +/** + * folio_xor_flags_has_waiters - Change some folio flags. + * @folio: The folio. + * @mask: Bits set in this word will be changed. + * + * This must only be used for flags which are changed with the folio + * lock held. For example, it is unsafe to use for PG_dirty as that + * can be set without the folio lock held. It can also only be used + * on flags which are in the range 0-6 as some of the implementations + * only affect those bits. + * + * Return: Whether there are tasks waiting on the folio. + */ +static inline bool folio_xor_flags_has_waiters(struct folio *folio, + unsigned long mask) +{ + return xor_unlock_is_negative_byte(mask, folio_flags(folio, 0)); +} + /** * folio_test_uptodate - Is this folio up to date? * @folio: The folio. diff --git a/mm/filemap.c b/mm/filemap.c index 330e21da6863..8262b85593be 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1499,7 +1499,7 @@ void folio_unlock(struct folio *folio) BUILD_BUG_ON(PG_waiters != 7); BUILD_BUG_ON(PG_locked > 7); VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); - if (xor_unlock_is_negative_byte(1 << PG_locked, folio_flags(folio, 0))) + if (folio_xor_flags_has_waiters(folio, 1 << PG_locked)) folio_wake_bit(folio, PG_locked); } EXPORT_SYMBOL(folio_unlock); @@ -1520,9 +1520,17 @@ EXPORT_SYMBOL(folio_unlock); */ void folio_end_read(struct folio *folio, bool success) { + unsigned long mask = 1 << PG_locked; + + /* Must be in bottom byte for x86 to work */ + BUILD_BUG_ON(PG_uptodate > 7); + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio); + if (success) - folio_mark_uptodate(folio); - folio_unlock(folio); + mask |= 1 << PG_uptodate; + if (folio_xor_flags_has_waiters(folio, mask)) + folio_wake_bit(folio, PG_locked); } EXPORT_SYMBOL(folio_end_read);