From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f169.google.com (mail-pd0-f169.google.com [209.85.192.169]) by kanga.kvack.org (Postfix) with ESMTP id 6B6FC6B0085 for ; Wed, 19 Nov 2014 18:32:38 -0500 (EST) Received: by mail-pd0-f169.google.com with SMTP id fp1so1825727pdb.0 for ; Wed, 19 Nov 2014 15:32:38 -0800 (PST) Received: from lgeamrelo01.lge.com (lgeamrelo01.lge.com. [156.147.1.125]) by mx.google.com with ESMTP id ra6si768224pbb.60.2014.11.19.15.32.35 for ; Wed, 19 Nov 2014 15:32:37 -0800 (PST) Date: Thu, 20 Nov 2014 08:32:32 +0900 From: Minchan Kim Subject: Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails Message-ID: <20141119233232.GA2627@bbox> References: <1415926147-9023-1-git-send-email-minchan@kernel.org> <20141118152336.d58b7b61a711b7d9982deb9d@linux-foundation.org> <20141118235201.GB7393@bbox> <20141119131535.7d848c148535c076a17b9d29@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20141119131535.7d848c148535c076a17b9d29@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Nitin Gupta , Jerome Marchand , Sergey Senozhatsky , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Matthew Wilcox , Karam Lee , Dave Chinner Hello, On Wed, Nov 19, 2014 at 01:15:35PM -0800, Andrew Morton wrote: > 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 It's not bdev_read_page but upper functions. (ie, do_mpage_readpage, swap_readpage, __mpage_writepage, __swap_writepage) > how the bio I/O complete handler (which one?) gets involved. bio->bi_end_io. > > 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. Indeed. I was terrible. Hope this is better.