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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 7028BC433ED for ; Thu, 13 May 2021 14:52:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E8E1261433 for ; Thu, 13 May 2021 14:52:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E8E1261433 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4D64C6B0036; Thu, 13 May 2021 10:52:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 485F56B006E; Thu, 13 May 2021 10:52:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 34DE06B0070; Thu, 13 May 2021 10:52:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0243.hostedemail.com [216.40.44.243]) by kanga.kvack.org (Postfix) with ESMTP id 074326B0036 for ; Thu, 13 May 2021 10:52:04 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 890E0181AF5CC for ; Thu, 13 May 2021 14:52:04 +0000 (UTC) X-FDA: 78136497768.12.3818A43 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf26.hostedemail.com (Postfix) with ESMTP id 504A240002E2 for ; Thu, 13 May 2021 14:51:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=H1NmysONfH93wRxMzbKIRXMjO3sQy9N1aOQConHhku0=; b=j0U7U0KxCjG8TbXLUokLW8ygK4 unQ5UMYf+It+N2ARfOjZrJUGd7raTpl84OmLbbydENw/nOS6I/ySHPrIBlTK86QPnCnT94yZL6lSY VCTmecp5NB+CiHdvaxcktwj55f2yaubMcP/6DD/23YUZ6z4xyk5FthNt7tHt6Skbas0IcEdD6D9fX WoxcuTkvUkO3e+w3qCeEqpHjXGt+X/OLX1t9sHVC9286L4izzDh1/EGdDGLQKESrIVIQ5Swz1T6TZ /RdWq8rD4m7LYJ5mwp1sRhlEPvk6v9rPITP6/Ch/Qn1NQ7q8FwC0xZAJhkTzR+lfcNx0H3oEMM+ip i/bpWC5A==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lhCfh-009W9H-1T; Thu, 13 May 2021 14:50:52 +0000 Date: Thu, 13 May 2021 15:50:41 +0100 From: Matthew Wilcox To: akpm@linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v10 00/33] Memory folios Message-ID: References: <20210511214735.1836149-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210511214735.1836149-1-willy@infradead.org> Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=j0U7U0Kx; dmarc=none; spf=none (imf26.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 504A240002E2 X-Stat-Signature: ytyp1wkubsrw6srmexg5njsgcgg1dkw3 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf26; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620917509-704471 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 11, 2021 at 10:47:02PM +0100, Matthew Wilcox (Oracle) wrote: > We also waste a lot of instructions ensuring that we're not looking at > a tail page. Almost every call to PageFoo() contains one or more hidden > calls to compound_head(). This also happens for get_page(), put_page() > and many more functions. There does not appear to be a way to tell gcc > that it can cache the result of compound_head(), nor is there a way to > tell it that compound_head() is idempotent. I instrumented _compound_head() on a test VM: +++ b/include/linux/page-flags.h @@ -179,10 +179,13 @@ enum pageflags { #ifndef __GENERATING_BOUNDS_H +extern atomic_t chcc; + static inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); + atomic_inc(&chcc); if (unlikely(head & 1)) return head - 1; return (unsigned long)page; which means it catches both calls to compound_head() and page_folio(). Between patch 8/96 in folio_v9 and patch 96/96, the number of calls in an idle VM went down from almost 7k/s to just over 5k/s; about 25%.