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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2399CC433FE for ; Wed, 3 Nov 2021 21:43:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1710F610EA for ; Wed, 3 Nov 2021 21:43:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 1710F610EA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 833C06B006C; Wed, 3 Nov 2021 17:43:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7E2786B0072; Wed, 3 Nov 2021 17:43:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D0BA6B0073; Wed, 3 Nov 2021 17:43:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0065.hostedemail.com [216.40.44.65]) by kanga.kvack.org (Postfix) with ESMTP id 5CEA16B006C for ; Wed, 3 Nov 2021 17:43:54 -0400 (EDT) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 1B2651850E7D3 for ; Wed, 3 Nov 2021 21:43:54 +0000 (UTC) X-FDA: 78768946746.10.778A4EF Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf10.hostedemail.com (Postfix) with ESMTP id 9D6836001981 for ; Wed, 3 Nov 2021 21:43:42 +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=6fB7Iv/vTAGVpFaMyL4RC5bfNZ1EkOgkaTbl7yf+osU=; b=rAaAhiBgZ/s/ebe2VxmLb/GcAa 6j8WBKDdATe866nlwbwsA6v+eQAU2hoXeuKIVN6TedPPfh1bDu4MW4AfOapoaFSDgz7kr9ZNrk8kG GvYY7i4RY7/lFdEwR6dTG6KhUhONoma0/A4x3L+lDjw1b7CTRLKAfoD2D/crOc3TMvBp7nQlW9JgL L0I14fkcRwwNQHnF+NSxXJu32zCVZ+jObzNTcQ9oe1K/tBbN5yAuQXVDpN/NgfHhMLwckVa5YtxDt xBJZD+eFUYrqLrkp44NacZL6RnnmnOb4afQz4CQJtRUxKnGYkdsY4zISw3uGwuq4XIA7lnrxScmaO PXQEeIAw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1miO15-005U8D-LY; Wed, 03 Nov 2021 21:42:24 +0000 Date: Wed, 3 Nov 2021 21:41:55 +0000 From: Matthew Wilcox To: Christophe JAILLET Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH] mm/mremap_pages: Save a few cycles in 'get_dev_pagemap()' Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 7ipen3qjjud4zgcz99qu1rhc8gz6yjjs X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9D6836001981 Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rAaAhiBg; dmarc=none; spf=none (imf10.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1635975822-384767 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 Wed, Nov 03, 2021 at 10:35:34PM +0100, Christophe JAILLET wrote: > Use 'percpu_ref_tryget_live_rcu()' instead of 'percpu_ref_tryget_live()' to > save a few cycles when it is known that the rcu lock is already > taken/released. If this is really important, we can add an __xa_load() which doesn't take the RCU read lock. I honestly think that the xarray is the wrong data structure here, and we'd be better off with a simple array of (start, pointer) tuples. > Signed-off-by: Christophe JAILLET > --- > mm/memremap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memremap.c b/mm/memremap.c > index 84de22c14567..012e8d23d365 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -506,7 +506,7 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn, > /* fall back to slow path lookup */ > rcu_read_lock(); > pgmap = xa_load(&pgmap_array, PHYS_PFN(phys)); > - if (pgmap && !percpu_ref_tryget_live(pgmap->ref)) > + if (pgmap && !percpu_ref_tryget_live_rcu(pgmap->ref)) > pgmap = NULL; > rcu_read_unlock(); > > -- > 2.30.2 > >