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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 81762C433EF for ; Tue, 4 Jan 2022 08:18:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EE9936B007D; Tue, 4 Jan 2022 03:18:02 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E72116B007E; Tue, 4 Jan 2022 03:18:02 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D3A366B0080; Tue, 4 Jan 2022 03:18:02 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0252.hostedemail.com [216.40.44.252]) by kanga.kvack.org (Postfix) with ESMTP id C11186B007D for ; Tue, 4 Jan 2022 03:18:02 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 7721D18195407 for ; Tue, 4 Jan 2022 08:18:02 +0000 (UTC) X-FDA: 78991901604.24.BD3AE88 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf28.hostedemail.com (Postfix) with ESMTP id 22128C000D for ; Tue, 4 Jan 2022 08:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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=03DwN3sfpSuEE5tC5xkBqsXfZ6yGIEsyQDiXYz6q4sE=; b=BIKYbD2id3e+lcSe8fmKamVRzG 2pQiRvDyKzZ1jn9r8sAPeGNAPnwWlRp2EJWwdCEuqnP3wtY38yhEtXsAzB7i/mGvTTtu11A5B17lJ j1Ypaqg7i63XLnkK7fXfiOuV+nQK779ns83PC33DyHm7HNQwCICGq1AVLxaM8MfPYykCBnMOPMAN3 mL764c+0BcMk5PZTxfVwyv+S+CMI0LDpYXtDb5ydJzs4PMq9L2lJ6biom4psw03lxzNc8U0wJb6Bb WO4HwFHrylOdOGUCbVUjbG+ocYYn72gypoWf6wP1RdVISZyfrq86QofnMGNHcx40abx3po9njVSTi 7lnuXepQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1n4f16-00Ahtr-Oh; Tue, 04 Jan 2022 08:18:00 +0000 Date: Tue, 4 Jan 2022 00:18:00 -0800 From: Christoph Hellwig To: "Matthew Wilcox (Oracle)" Cc: linux-mm@kvack.org, John Hubbard , Andrew Morton Subject: Re: [PATCH 05/17] gup: Add try_get_folio() Message-ID: References: <20220102215729.2943705-1-willy@infradead.org> <20220102215729.2943705-6-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220102215729.2943705-6-willy@infradead.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: 22128C000D X-Stat-Signature: w1jc388u7bm9uuc3th5u3aiy4d8mo3ky Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=BIKYbD2i; dmarc=none; spf=none (imf28.hostedemail.com: domain of BATV+e6cc8b46eea779d11ede+6708+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+e6cc8b46eea779d11ede+6708+infradead.org+hch@bombadil.srs.infradead.org X-Rspamd-Server: rspam02 X-HE-Tag: 1641284281-978021 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 Sun, Jan 02, 2022 at 09:57:17PM +0000, Matthew Wilcox (Oracle) wrote: > This replaces try_get_compound_head(). It includes a small optimisation > for the race where a folio is split between being looked up from its > tail page and the reference count being obtained. Before, it returned > NULL, which presumably triggered a retry under the mmap_lock, whereas > now it will retry without the lock. Finding a frozen page will still > return NULL. Looks good: Reviewed-by: Christoph Hellwig Although I think splitting out the rety optimization into a separate patch would be nicer to document the change and to ease bisection if that arises.