From patchwork Thu Sep 17 15:10:38 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 11782745 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 024EA14F6 for ; Thu, 17 Sep 2020 15:12:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6DE82137B for ; Thu, 17 Sep 2020 15:12:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ffihf+5N" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727980AbgIQPMl (ORCPT ); Thu, 17 Sep 2020 11:12:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727483AbgIQPL0 (ORCPT ); Thu, 17 Sep 2020 11:11:26 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3F991C06178A; Thu, 17 Sep 2020 08:10:54 -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=zXmx2Q9ib8LaEq/cmNv7DtrHg7rQIIRhLXukJQtl2ug=; b=ffihf+5NKGdlu+XW5it3GHqzVB wV8ybsOqFAy9WktF9PdPXd2BwOQSZANCWWHyXH/mEtngJKZf3xOEoD9JCKHw4+g0OfYJhOc7AVHQt 0gVu68YvUMnq1NxaLz4/tNIjq6X8ua6zUp61z7DR7po/TtyHZqAGyOz8Qmm34stw6FLTlWzyQU6q8 zXEfP6psDDzJxwpQ37M6Vy63mhmgRcc+ySyhcVXVUyv2+3LUWSotVTI55QattpfbF6nlaRo1GDL2O qMZwLGHUezabQa6mru/yTdiLJl/oC5Uym3hl6B7ZdxB6DB89vrx3fYbLzg2Qq8u59Wa6KAzr+PRZQ 57dfGvYQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIvYi-0001PJ-AR; Thu, 17 Sep 2020 15:10:52 +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 Subject: [PATCH 01/13] mm: Add AOP_UPDATED_PAGE return value Date: Thu, 17 Sep 2020 16:10:38 +0100 Message-Id: <20200917151050.5363-2-willy@infradead.org> X-Mailer: git-send-email 2.21.3 In-Reply-To: <20200917151050.5363-1-willy@infradead.org> References: <20200917151050.5363-1-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 | 12 ++++++++++-- 4 files changed, 33 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 e019ea2f1347..6fc650050d20 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..131a2aaa1537 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2254,8 +2254,10 @@ 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) + goto page_ok; if (unlikely(error)) { if (error == AOP_TRUNCATED_PAGE) { @@ -2619,7 +2621,7 @@ 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 +2656,8 @@ 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 +2871,10 @@ 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);