From patchwork Thu Jul 2 16:51:18 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andreas Gruenbacher X-Patchwork-Id: 11639815 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 833286C1 for ; Thu, 2 Jul 2020 16:51:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BAEB2088E for ; Thu, 2 Jul 2020 16:51:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fadzxGD/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726929AbgGBQve (ORCPT ); Thu, 2 Jul 2020 12:51:34 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:38817 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726300AbgGBQvd (ORCPT ); Thu, 2 Jul 2020 12:51:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593708691; 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=lasbI7WSZBNJiaWUYinp95/I+mBtTJm3Z60zJ8X/hrU=; b=fadzxGD/XkDTPnAnphYgEF7C53oeR3Fgq3s/e+SVtRk+NtHxJuUGiAbZWBESYNtoFBVy+2 zr0cZIUlGabLrkyWgnYeRqCBV1FHo6U34HHxD54rpuZpX/SUy+XXgMjqCVgLVBKEUBK/Zo 4/Vr49tnK5P2OqTe36gcw+jAoZjJUTM= 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-79-sU6N5AAGOCmW1YN2G2tkNA-1; Thu, 02 Jul 2020 12:51:30 -0400 X-MC-Unique: sU6N5AAGOCmW1YN2G2tkNA-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 DA29513E9C1; Thu, 2 Jul 2020 16:51:28 +0000 (UTC) Received: from max.home.com (unknown [10.40.192.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1F5E979231; Thu, 2 Jul 2020 16:51:26 +0000 (UTC) From: Andreas Gruenbacher To: Matthew Wilcox Cc: Dave Chinner , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Gruenbacher Subject: [RFC 2/4] fs: Add IOCB_NOIO flag for generic_file_read_iter Date: Thu, 2 Jul 2020 18:51:18 +0200 Message-Id: <20200702165120.1469875-3-agruenba@redhat.com> In-Reply-To: <20200702165120.1469875-1-agruenba@redhat.com> References: <20200702165120.1469875-1-agruenba@redhat.com> MIME-Version: 1.0 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 | 16 ++++++++++++++-- 2 files changed, 15 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..e8318f99f468 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, @@ -2038,12 +2038,16 @@ 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); } if (!PageUptodate(page)) { - if (iocb->ki_flags & IOCB_NOWAIT) { + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) { put_page(page); goto would_block; } @@ -2249,6 +2253,14 @@ 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 issuing I/O requests; + * this doesn't prevent readahead. The IOCB_NOIO flag indicates that + * -EAGAIN shall be returned when no data can be read without issuing + * I/O requests, and 0 shall be returned when readhead would be + * triggered. + * * Return: * * number of bytes copied, even for partial reads * * negative error code if nothing was read