From patchwork Fri Oct 9 14:30:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 269007 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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 4DB08C2BD0C for ; Fri, 9 Oct 2020 14:31:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06A63222BA for ; Fri, 9 Oct 2020 14:31:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="BiC282mR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388893AbgJIObU (ORCPT ); Fri, 9 Oct 2020 10:31:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53618 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388880AbgJIObR (ORCPT ); Fri, 9 Oct 2020 10:31:17 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 50174C0613DC; Fri, 9 Oct 2020 07:31:14 -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=ck7tjnyWrUbu2fgU3wEmHKO8ECkKRvYNOzxLe93kaKs=; b=BiC282mRNnUukNWWTqgtbnhsqu 2W6Gbvyh9SISCymJu5kFXw5QdqjGbdQzamuQbRf1rL8tiIeP0p40GR7yl2ar7Eb+6xSyY8upJelEN ntmagHzfaNWfBwLcJVs3aeWLtV3tJpfcnnVa/yp99qw7rtgUWxNDXTTwII/m5GhJ7TlS+CpNQSQhq wA1CvIYl0LWqu3b5YY0VMcEG1BR4mSICeWJ+Ox/QHS1wPbDG6jm7ZN6TzE2IVH0Yu8DWdd5pc6FLh yslfa5C0Y3/JNM4OSc4GK5KFNVIm0ZICpAtFs9Hxnm8fI9rz5cJBc/h+X0blwHudPVU8k6vDV6Cvz t42dWX/g==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQtQI-0005uT-Hr; Fri, 09 Oct 2020 14:31:06 +0000 From: "Matthew Wilcox (Oracle)" To: linux-fsdevel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , linux-mm@kvack.org, v9fs-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org, ecryptfs@vger.kernel.org, linux-um@lists.infradead.org, linux-mtd@lists.infradead.org, Richard Weinberger , linux-xfs@vger.kernel.org Subject: [PATCH v2 01/16] mm: Add AOP_UPDATED_PAGE return value Date: Fri, 9 Oct 2020 15:30:49 +0100 Message-Id: <20201009143104.22673-2-willy@infradead.org> X-Mailer: git-send-email 2.21.3 In-Reply-To: <20201009143104.22673-1-willy@infradead.org> References: <20201009143104.22673-1-willy@infradead.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org Allow synchronous ->readpage implementations to execute more efficiently by skipping the re-locking of the page. Signed-off-by: Matthew Wilcox (Oracle) --- Documentation/filesystems/locking.rst | 7 ++++--- Documentation/filesystems/vfs.rst | 21 ++++++++++++++------- include/linux/fs.h | 5 +++++ mm/filemap.c | 15 +++++++++++++-- 4 files changed, 36 insertions(+), 12 deletions(-) diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 64f94a18d97e..06a7a8bf2362 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -269,7 +269,7 @@ locking rules: ops PageLocked(page) i_rwsem ====================== ======================== ========= writepage: yes, unlocks (see below) -readpage: yes, unlocks +readpage: yes, may unlock writepages: set_page_dirty no readahead: yes, unlocks @@ -294,8 +294,9 @@ swap_deactivate: no ->write_begin(), ->write_end() and ->readpage() may be called from the request handler (/dev/loop). -->readpage() unlocks the page, either synchronously or via I/O -completion. +->readpage() may return AOP_UPDATED_PAGE if the page is now Uptodate +or 0 if the page will be unlocked asynchronously by I/O completion. +If it returns -errno, it should unlock the page. ->readahead() unlocks the pages that I/O is attempted on like ->readpage(). diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index ca52c82e5bb5..16248c299aaa 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -643,7 +643,7 @@ set_page_dirty to write data into the address_space, and writepage and writepages to writeback data to storage. Adding and removing pages to/from an address_space is protected by the -inode's i_mutex. +inode's i_rwsem held exclusively. When data is written to a page, the PG_Dirty flag should be set. It typically remains set until writepage asks for it to be written. This @@ -757,12 +757,19 @@ cache in your filesystem. The following members are defined: ``readpage`` called by the VM to read a page from backing store. The page - will be Locked when readpage is called, and should be unlocked - and marked uptodate once the read completes. If ->readpage - discovers that it needs to unlock the page for some reason, it - can do so, and then return AOP_TRUNCATED_PAGE. In this case, - the page will be relocated, relocked and if that all succeeds, - ->readpage will be called again. + will be Locked and !Uptodate when readpage is called. Ideally, + the filesystem will bring the page Uptodate and return + AOP_UPDATED_PAGE. If the filesystem encounters an error, it + should unlock the page and return a negative errno without marking + the page Uptodate. It does not need to mark the page as Error. + If the filesystem returns 0, this means the page will be unlocked + asynchronously by I/O completion. The VFS will wait for the + page to be unlocked, so there is no advantage to executing this + operation asynchronously. + + The filesystem can also return AOP_TRUNCATED_PAGE to indicate + that it had to unlock the page to avoid a deadlock. The caller + will re-check the page cache and call ->readpage again. ``writepages`` called by the VM to write out pages associated with the diff --git a/include/linux/fs.h b/include/linux/fs.h index 7519ae003a08..badf80e133fd 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -273,6 +273,10 @@ struct iattr { * reference, it should drop it before retrying. Returned * by readpage(). * + * @AOP_UPDATED_PAGE: The readpage method has brought the page Uptodate + * without releasing the page lock. This is suitable for synchronous + * implementations of readpage. + * * address_space_operation functions return these large constants to indicate * special semantics to the caller. These are much larger than the bytes in a * page to allow for functions that return the number of bytes operated on in a @@ -282,6 +286,7 @@ struct iattr { enum positive_aop_returns { AOP_WRITEPAGE_ACTIVATE = 0x80000, AOP_TRUNCATED_PAGE = 0x80001, + AOP_UPDATED_PAGE = 0x80002, }; #define AOP_FLAG_CONT_EXPAND 0x0001 /* called from cont_expand */ diff --git a/mm/filemap.c b/mm/filemap.c index 1aaea26556cc..95b68ec1f22c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2254,8 +2254,13 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, * PG_error will be set again if readpage fails. */ ClearPageError(page); - /* Start the actual read. The read will unlock the page. */ + /* Start the actual read. The read may unlock the page. */ error = mapping->a_ops->readpage(filp, page); + if (error == AOP_UPDATED_PAGE) { + unlock_page(page); + error = 0; + goto page_ok; + } if (unlikely(error)) { if (error == AOP_TRUNCATED_PAGE) { @@ -2619,7 +2624,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) */ if (unlikely(!PageUptodate(page))) goto page_not_uptodate; - +page_ok: /* * We've made it this far and we had to drop our mmap_lock, now is the * time to return to the upper layer and have it re-find the vma and @@ -2654,6 +2659,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) ClearPageError(page); fpin = maybe_unlock_mmap_for_io(vmf, fpin); error = mapping->a_ops->readpage(file, page); + if (error == AOP_UPDATED_PAGE) + goto page_ok; if (!error) { wait_on_page_locked(page); if (!PageUptodate(page)) @@ -2867,6 +2874,10 @@ static struct page *do_read_cache_page(struct address_space *mapping, err = filler(data, page); else err = mapping->a_ops->readpage(data, page); + if (err == AOP_UPDATED_PAGE) { + unlock_page(page); + goto out; + } if (err < 0) { put_page(page);