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s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=OHbnhUmSKXKUNQXDuUhAYkDR4SHYPZJ41RILLR4eq0o=; b=WJD6WJqsGwCY3P1j5e3ovPL//F 5RbS0a3Lg88hg9MB0jYULiy/rFKJzbGCbrOapYTb266XbbyKA8CTrtvek66/nG33VaFg7VdMBRbZR rnPMGsBm9j06adyP+A8QTZhRk0UEwOFu8zRa/WX5OeKUuZ+8YrF+LcaXS/z87nWR3tKlZ6cwW0Syp kq9Y5/xMHFDtxNLwNsH9lKI3RuLMynoTNQK4hzK4Vqwfsf9J1ZXgGgduQBDRr8PlJm3OFdHS6ZrwQ 3fhRurJFVDu4wmnenxltcI7MoWu83uWJo+ueqXyOwnSdoY74gjndAyvqk62MAvIAKmI/huMjFZFAX h7v56bTQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lNn6Q-006Ymd-I3; Sun, 21 Mar 2021 01:42:05 +0000 Date: Sun, 21 Mar 2021 01:42:02 +0000 From: Matthew Wilcox To: David Howells Cc: Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, David Wysochanski , Alexander Viro , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 08/28] netfs: Provide readahead and readpage netfs helpers Message-ID: <20210321014202.GF3420@casper.infradead.org> References: <161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk> <161539537375.286939.16642940088716990995.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161539537375.286939.16642940088716990995.stgit@warthog.procyon.org.uk> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: E06916000100 X-Stat-Signature: wmmqnrc4cq5bygke4yqd9hnnqwetxrbk Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf25; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616290960-906552 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 10, 2021 at 04:56:13PM +0000, David Howells wrote: > +void netfs_readahead(struct readahead_control *ractl, > + const struct netfs_read_request_ops *ops, > + void *netfs_priv) > +{ > + struct netfs_read_request *rreq; > + struct page *page; > + unsigned int debug_index = 0; > + > + _enter("%lx,%x", readahead_index(ractl), readahead_count(ractl)); > + > + if (readahead_count(ractl) == 0) > + goto cleanup; > + > + rreq = netfs_alloc_read_request(ops, netfs_priv, ractl->file); > + if (!rreq) > + goto cleanup; > + rreq->mapping = ractl->mapping; > + rreq->start = readahead_pos(ractl); > + rreq->len = readahead_length(ractl); > + > + netfs_rreq_expand(rreq, ractl); > + > + atomic_set(&rreq->nr_rd_ops, 1); > + do { > + if (!netfs_rreq_submit_slice(rreq, &debug_index)) > + break; > + > + } while (rreq->submitted < rreq->len); > + > + while ((page = readahead_page(ractl))) > + put_page(page); You don't need this pair of lines (unless I'm missing something). read_pages() in mm/readahead.c puts the reference and unlocks any pages which are not read by the readahead op. Indeed, I think doing this is buggy because you don't unlock the page. > + /* If we decrement nr_rd_ops to 0, the ref belongs to us. */ > + if (atomic_dec_and_test(&rreq->nr_rd_ops)) > + netfs_rreq_assess(rreq, false); > + return; > + > +cleanup: > + if (netfs_priv) > + ops->cleanup(ractl->mapping, netfs_priv); > + return; > +} > +EXPORT_SYMBOL(netfs_readahead); > +int netfs_readpage(struct file *file, > + struct page *page, > + const struct netfs_read_request_ops *ops, > + void *netfs_priv) > +{ > + struct netfs_read_request *rreq; > + unsigned int debug_index = 0; > + int ret; > + > + _enter("%lx", page->index); > + > + rreq = netfs_alloc_read_request(ops, netfs_priv, file); > + if (!rreq) { > + if (netfs_priv) > + ops->cleanup(netfs_priv, page->mapping); > + unlock_page(page); > + return -ENOMEM; > + } > + rreq->mapping = page->mapping; FYI, this isn't going to work with swap-over-NFS. You have to use page_file_mapping(). > + rreq->start = page->index * PAGE_SIZE; and page_index() here. I rather dislike it that swap-over-NFS uses readpage which makes this need to exist. If somebody were to switch SWP_FS_OPS to using kiocbs, some of this pain could go away.