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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 EE5CCC433E0 for ; Fri, 3 Jul 2020 09:53:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAD5920836 for ; Fri, 3 Jul 2020 09:53:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VHu7N1Kg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726152AbgGCJxm (ORCPT ); Fri, 3 Jul 2020 05:53:42 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:41077 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725915AbgGCJxf (ORCPT ); Fri, 3 Jul 2020 05:53:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593770013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=H3F7Np/uM/15jpMjri5ryOy3uvdVrn3PYgDhCmIq6hw=; b=VHu7N1KgO+LkAB0yNVNU7MftNrb8HBg3gc9k49D0itahg9FcOsIi4yMyv2idXMm+WV+dJf EpckcxV3tjuNE1IYZlIIOrt9LxrsqkVD2G/QpJuh65vcF7au/nTqyt2h5TeXYBp7D2hmMT sW1wsrpsaRRqV7/jHHlUe+1SZQEtoN0= 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-144-g2LTuadCPpCwQwFgSo78mw-1; Fri, 03 Jul 2020 05:53:32 -0400 X-MC-Unique: g2LTuadCPpCwQwFgSo78mw-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 1109F107ACF4; Fri, 3 Jul 2020 09:53:31 +0000 (UTC) Received: from max.home.com (unknown [10.40.192.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id 494ED6111F; Fri, 3 Jul 2020 09:53:29 +0000 (UTC) From: Andreas Gruenbacher To: Linus Torvalds Cc: Matthew Wilcox , Dave Chinner , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Gruenbacher Subject: [RFC v2 1/2] fs: Add IOCB_NOIO flag for generic_file_read_iter Date: Fri, 3 Jul 2020 11:53:24 +0200 Message-Id: <20200703095325.1491832-2-agruenba@redhat.com> In-Reply-To: <20200703095325.1491832-1-agruenba@redhat.com> References: <20200703095325.1491832-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it shouldn't trigger any filesystem I/O for the actual request or for readahead. This allows to do tentative reads out of the page cache as some filesystems allow, and to take the appropriate locks and retry the reads only if the requested pages are not cached. Signed-off-by: Andreas Gruenbacher --- include/linux/fs.h | 1 + mm/filemap.c | 17 +++++++++++++++-- 2 files changed, 16 insertions(+), 2 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 3f881a892ea7..1ab2ea19e883 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -315,6 +315,7 @@ enum rw_hint { #define IOCB_SYNC (1 << 5) #define IOCB_WRITE (1 << 6) #define IOCB_NOWAIT (1 << 7) +#define IOCB_NOIO (1 << 8) struct kiocb { struct file *ki_filp; diff --git a/mm/filemap.c b/mm/filemap.c index f0ae9a6308cb..22f7ff2d369e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2028,7 +2028,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, page = find_get_page(mapping, index); if (!page) { - if (iocb->ki_flags & IOCB_NOWAIT) + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) goto would_block; page_cache_sync_readahead(mapping, ra, filp, @@ -2038,6 +2038,10 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, goto no_cached_page; } if (PageReadahead(page)) { + if (iocb->ki_flags & IOCB_NOIO) { + put_page(page); + goto out; + } page_cache_async_readahead(mapping, ra, filp, page, index, last_index - index); @@ -2249,9 +2253,18 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read); * * This is the "read_iter()" routine for all filesystems * that can use the page cache directly. + * + * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall + * be returned when no data can be read without waiting for I/O requests + * to complete; it doesn't prevent readahead. + * + * The IOCB_NOIO flag in iocb->ki_flags indicates that -EAGAIN shall be + * returned when no data can be read without issuing new I/O requests, + * and 0 shall be returned when readhead would have been triggered. + * * Return: * * number of bytes copied, even for partial reads - * * negative error code if nothing was read + * * negative error code (or 0 if IOCB_NOIO) if nothing was read */ ssize_t generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) -- 2.26.2