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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 909F4C34035 for ; Tue, 18 Feb 2020 06:21:59 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4FE8420722 for ; Tue, 18 Feb 2020 06:21:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4FE8420722 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48M9jx3YGpzDqTx for ; Tue, 18 Feb 2020 17:21:57 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.helo=mail105.syd.optusnet.com.au (client-ip=211.29.132.249; helo=mail105.syd.optusnet.com.au; envelope-from=david@fromorbit.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Received: from mail105.syd.optusnet.com.au (mail105.syd.optusnet.com.au [211.29.132.249]) by lists.ozlabs.org (Postfix) with ESMTP id 48M9jq6SwmzDqQL for ; Tue, 18 Feb 2020 17:21:49 +1100 (AEDT) Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id D25FD3A2514; Tue, 18 Feb 2020 17:21:48 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j3wGR-0006EU-Pg; Tue, 18 Feb 2020 17:21:47 +1100 Date: Tue, 18 Feb 2020 17:21:47 +1100 From: Dave Chinner To: Matthew Wilcox Subject: Re: [PATCH v6 08/19] mm: Add readahead address space operation Message-ID: <20200218062147.GN10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-14-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200217184613.19668-14-willy@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=zAxSp4fFY/GQY8/esVNjqw==:117 a=zAxSp4fFY/GQY8/esVNjqw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=l697ptgUJYAA:10 a=JfrnYn6hAAAA:8 a=7-415B0cAAAA:8 a=ZUKaNjAUM_NwrQaOQj4A:9 a=JQFMNDVPDCAknBdf:21 a=DU4q-3mnrf8zicIu:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" On Mon, Feb 17, 2020 at 10:45:54AM -0800, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > This replaces ->readpages with a saner interface: > - Return void instead of an ignored error code. > - Pages are already in the page cache when ->readahead is called. Might read better as: - Page cache is already populates with locked pages when ->readahead is called. > - Implementation looks up the pages in the page cache instead of > having them passed in a linked list. Add: - cleanup of unused readahead handled by ->readahead caller, not the method implementation. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > Documentation/filesystems/locking.rst | 6 +++++- > Documentation/filesystems/vfs.rst | 13 +++++++++++++ > include/linux/fs.h | 2 ++ > include/linux/pagemap.h | 18 ++++++++++++++++++ > mm/readahead.c | 8 +++++++- > 5 files changed, 45 insertions(+), 2 deletions(-) > > diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst > index 5057e4d9dcd1..0ebc4491025a 100644 > --- a/Documentation/filesystems/locking.rst > +++ b/Documentation/filesystems/locking.rst > @@ -239,6 +239,7 @@ prototypes:: > int (*readpage)(struct file *, struct page *); > int (*writepages)(struct address_space *, struct writeback_control *); > int (*set_page_dirty)(struct page *page); > + void (*readahead)(struct readahead_control *); > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > int (*write_begin)(struct file *, struct address_space *mapping, > @@ -271,7 +272,8 @@ writepage: yes, unlocks (see below) > readpage: yes, unlocks > writepages: > set_page_dirty no > -readpages: > +readahead: yes, unlocks > +readpages: no > write_begin: locks the page exclusive > write_end: yes, unlocks exclusive > bmap: > @@ -295,6 +297,8 @@ the request handler (/dev/loop). > ->readpage() unlocks the page, either synchronously or via I/O > completion. > > +->readahead() unlocks the pages like ->readpage(). > + "... the pages that I/O is attempted on ..." > ->readpages() populates the pagecache with the passed pages and starts > I/O against them. They come unlocked upon I/O completion. > > diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst > index 7d4d09dd5e6d..81ab30fbe45c 100644 > --- a/Documentation/filesystems/vfs.rst > +++ b/Documentation/filesystems/vfs.rst > @@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined: > int (*readpage)(struct file *, struct page *); > int (*writepages)(struct address_space *, struct writeback_control *); > int (*set_page_dirty)(struct page *page); > + void (*readahead)(struct readahead_control *); > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > int (*write_begin)(struct file *, struct address_space *mapping, > @@ -781,12 +782,24 @@ cache in your filesystem. The following members are defined: > If defined, it should set the PageDirty flag, and the > PAGECACHE_TAG_DIRTY tag in the radix tree. > > +``readahead`` > + Called by the VM to read pages associated with the address_space > + object. The pages are consecutive in the page cache and are > + locked. The implementation should decrement the page refcount > + after starting I/O on each page. Usually the page will be > + unlocked by the I/O completion handler. If the function does > + not attempt I/O on some pages, the caller will decrement the page > + refcount and unlock the pages for you. Set PageUptodate if the > + I/O completes successfully. Setting PageError on any page will > + be ignored; simply unlock the page if an I/O error occurs. > + > ``readpages`` > called by the VM to read pages associated with the address_space > object. This is essentially just a vector version of readpage. > Instead of just one page, several pages are requested. > readpages is only used for read-ahead, so read errors are > ignored. If anything goes wrong, feel free to give up. > + This interface is deprecated; implement readahead instead. What is the removal schedule for the deprecated interface? > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 3613154e79e4..bd4291f78f41 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -665,6 +665,24 @@ static inline void readahead_next(struct readahead_control *rac) > #define readahead_for_each(rac, page) \ > for (; (page = readahead_page(rac)); readahead_next(rac)) > > +/* The byte offset into the file of this readahead block */ > +static inline loff_t readahead_offset(struct readahead_control *rac) > +{ > + return (loff_t)rac->_start * PAGE_SIZE; > +} Urk. Didn't an early page use "offset" for the page index? That was was "mm: Remove 'page_offset' from readahead loop" did, right? That's just going to cause confusion to have different units for readahead "offsets".... > + > +/* The number of bytes in this readahead block */ > +static inline loff_t readahead_length(struct readahead_control *rac) > +{ > + return (loff_t)rac->_nr_pages * PAGE_SIZE; > +} > + > +/* The index of the first page in this readahead block */ > +static inline unsigned int readahead_index(struct readahead_control *rac) > +{ > + return rac->_start; > +} Based on this, I suspect the earlier patch should use "index" rather than "offset" when walking the page cache indexes... > + > /* The number of pages in this readahead block */ > static inline unsigned int readahead_count(struct readahead_control *rac) > { > diff --git a/mm/readahead.c b/mm/readahead.c > index 9e430daae42f..975ff5e387be 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -121,7 +121,13 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages) > > blk_start_plug(&plug); > > - if (aops->readpages) { > + if (aops->readahead) { > + aops->readahead(rac); > + readahead_for_each(rac, page) { > + unlock_page(page); > + put_page(page); > + } This needs a comment to explain the unwinding that needs to be done here. I'm not going to remember in a year's time that this is just for the pages that weren't submitted by ->readahead.... Cheers, Dave. -- Dave Chinner david@fromorbit.com