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=-6.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 21B18C4338F for ; Thu, 12 Aug 2021 12:57:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E1EE360F35 for ; Thu, 12 Aug 2021 12:57:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237571AbhHLM5l (ORCPT ); Thu, 12 Aug 2021 08:57:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:48461 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237350AbhHLM5j (ORCPT ); Thu, 12 Aug 2021 08:57:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628773033; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=mCn72IsR7SruuxmCk9O65PvV6CJhIOfP9bZiMHWXYvw=; b=K8IWMSjCT9P0LzkYsTsLVVKIBeTnAXkbOPs/E/WR+xAjOvwU5G+2gzUHjzYYok9UkEv58l ucJeuigSgEJpNJHVK4ziI2TEdHwIxrH12jRJM/tKBkOLHjIeFTkn+mUCIzwd0VLfNJjvqc d54Ra2WGvOflfc4+XwsX79MzLhn+5yU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-391-hBfPyN1kPIaWh0iRWiHLJw-1; Thu, 12 Aug 2021 08:57:10 -0400 X-MC-Unique: hBfPyN1kPIaWh0iRWiHLJw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D465E8799EC; Thu, 12 Aug 2021 12:57:08 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.22.32.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id C811060C05; Thu, 12 Aug 2021 12:57:06 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20210812122104.GB18532@lst.de> References: <20210812122104.GB18532@lst.de> <162876946134.3068428.15475611190876694695.stgit@warthog.procyon.org.uk> <162876947840.3068428.12591293664586646085.stgit@warthog.procyon.org.uk> To: Christoph Hellwig Cc: dhowells@redhat.com, willy@infradead.org, trond.myklebust@primarydata.com, darrick.wong@oracle.com, jlayton@kernel.org, sfrench@samba.org, torvalds@linux-foundation.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm: Make swap_readpage() for SWP_FS_OPS use ->direct_IO() not ->readpage() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3085431.1628773025.1@warthog.procyon.org.uk> Date: Thu, 12 Aug 2021 13:57:05 +0100 Message-ID: <3085432.1628773025@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christoph Hellwig wrote: > On Thu, Aug 12, 2021 at 12:57:58PM +0100, David Howells wrote: > > Make swap_readpage(), when accessing a swap file (SWP_FS_OPS) use > > the ->direct_IO() method on the filesystem rather then ->readpage(). > > ->direct_IO is just a helper for ->read_iter and ->write_iter, so please > don't call it directly. It actually is slowly on its way out, with at > at least all of the iomap implementations not using it, as well as various > other file systems. [Note that __swap_writepage() uses ->direct_IO().] Calling ->write_iter is probably a bad idea here. Imagine that it goes through, say, generic_file_write_iter(), then __generic_file_write_iter() and then generic_file_direct_write(). It adds a number of delays into the system, including: - Taking the inode lock - Removing file privs - Cranking mtime, ctime, file version - Doing mnt_want_write - Setting the inode dirty - Waiting on pages in the range that are being written - Walking over the pagecache to invalidate the range - Redoing the invalidation (can't be skipped since page 0 is pinned) that we might want to skip as they'll end up being done for every page swapped out. > > + ki = kzalloc(sizeof(*ki), GFP_KERNEL); > > + if (!ki) > > + return -ENOMEM; > > for the synchronous case we could avoid this allocation and just use > arguments on stack. True. David