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=-6.9 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=ham 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 2BE7DC433E0 for ; Tue, 7 Jul 2020 14:45:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E0552078D for ; Tue, 7 Jul 2020 14:45:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RVqtSMX6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728259AbgGGOpJ (ORCPT ); Tue, 7 Jul 2020 10:45:09 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:29308 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726946AbgGGOpJ (ORCPT ); Tue, 7 Jul 2020 10:45:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594133108; 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=+Rc8UffssJDHnOarGy+MDwuizYchxVZvOHLs0Aalc1w=; b=RVqtSMX6hiznRGu9toC2JipZNziiTCl00h4jym/CyvpcXDTCt3UdFNQ4NTHB8eAnnifDU1 WoVydbhDSDCDdJuml4LpAINlNtVlhw76HoHfdTDbwisO1CBGcLeaXg/X+biZO0K0xWQbRe adN2SioZKcqrEcU+fWtyu9qIGt8Jx74= 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-460-IGP8yhUsNAq5HY_0rN31jA-1; Tue, 07 Jul 2020 10:45:05 -0400 X-MC-Unique: IGP8yhUsNAq5HY_0rN31jA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2C54B19057A0; Tue, 7 Jul 2020 14:45:04 +0000 (UTC) Received: from max.home.com (unknown [10.40.192.179]) by smtp.corp.redhat.com (Postfix) with ESMTP id 33C915F7D8; Tue, 7 Jul 2020 14:45:01 +0000 (UTC) From: Andreas Gruenbacher To: Linus Torvalds Cc: Matthew Wilcox , Dave Chinner , Jens Axboe , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Gruenbacher Subject: [RFC v3 1/2] fs: Add IOCB_NOIO flag for generic_file_read_iter Date: Tue, 7 Jul 2020 16:44:56 +0200 Message-Id: <20200707144457.1603400-2-agruenba@redhat.com> In-Reply-To: <20200707144457.1603400-1-agruenba@redhat.com> References: <20200707144457.1603400-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 | 23 +++++++++++++++++++++-- 2 files changed, 22 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..385759c4ce4b 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); @@ -2160,6 +2164,11 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, } readpage: + if (iocb->ki_flags & IOCB_NOIO) { + unlock_page(page); + put_page(page); + goto would_block; + } /* * A previous I/O error may have been due to temporary * failures, eg. multipath errors. @@ -2249,9 +2258,19 @@ 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 no new I/O + * requests shall be made for the read or for readahead. When no data + * can be read, -EAGAIN shall be returned. When readahead would be + * triggered, a partial, possibly empty read shall be returned. + * * 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