From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933653AbaKSVPj (ORCPT ); Wed, 19 Nov 2014 16:15:39 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:57643 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932873AbaKSVPg (ORCPT ); Wed, 19 Nov 2014 16:15:36 -0500 Date: Wed, 19 Nov 2014 13:15:35 -0800 From: Andrew Morton To: Minchan Kim Cc: Nitin Gupta , Jerome Marchand , Sergey Senozhatsky , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Matthew Wilcox , Karam Lee , Dave Chinner Subject: Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails Message-Id: <20141119131535.7d848c148535c076a17b9d29@linux-foundation.org> In-Reply-To: <20141118235201.GB7393@bbox> References: <1415926147-9023-1-git-send-email-minchan@kernel.org> <20141118152336.d58b7b61a711b7d9982deb9d@linux-foundation.org> <20141118235201.GB7393@bbox> X-Mailer: Sylpheed 3.4.0beta7 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 19 Nov 2014 08:52:01 +0900 Minchan Kim wrote: > > > > > > - /* > > > - * Return 0 prevents I/O fallback trial caused by rw_page fail > > > - * and upper layer can handle this IO error via page error. > > > - */ > > > + page_endio(page, rw, 0); > > > return 0; > > > > Losing the comment makes me sad. The code is somewhat odd-looking. We > > should add some words explaining why we're not reporting errors at this > > point. > > Okay. How about this? > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index decca6f161b8..1d7c90d5e0d0 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -975,6 +975,12 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, > err = zram_bvec_rw(zram, &bv, index, offset, rw); > out_unlock: > up_read(&zram->init_lock); > + /* > + * If I/O fails, just return error without calling page_endio. > + * It causes resubmit the I/O with bio request by rw_page fallback > + * and bio I/O complete handler does things to handle the error > + * (e.g., set_page_dirty of swap_writepage fail). > + */ > if (err == 0) > page_endio(page, rw, 0); > return err; I don't understand the comment :( bdev_read_page() doesn't resubmit the IO if block_device_operations.rw_page() returns zero and it's unclear how the bio I/O complete handler (which one?) gets involved. It would help in the comment was more specific. Instead of using vague terms like "rw_page fallback" and "bio I/O complete handler", use actual function names so the reader understand exactly what code we're referring to.