Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752850AbaBXPQ1 (ORCPT ); Mon, 24 Feb 2014 10:16:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38012 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752442AbaBXPQ0 (ORCPT ); Mon, 24 Feb 2014 10:16:26 -0500 Message-ID: <530B621E.9010309@redhat.com> Date: Mon, 24 Feb 2014 16:15:42 +0100 From: Jerome Marchand User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Joonsoo Kim CC: Joonsoo Kim , Andrew Morton , Minchan Kim , Nitin Gupta , LKML , Sergey Senozhatsky Subject: Re: [PATCH] zram: support REQ_DISCARD References: <1393221070-21674-1-git-send-email-iamjoonsoo.kim@lge.com> <530B4AFB.5060006@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/24/2014 04:02 PM, Joonsoo Kim wrote: > 2014-02-24 22:36 GMT+09:00 Jerome Marchand : >> On 02/24/2014 06:51 AM, Joonsoo Kim wrote: >>> zram is ram based block device and can be used by backend of filesystem. >>> When filesystem deletes a file, it normally doesn't do anything on data >>> block of that file. It just marks on metadata of that file. This behavior >>> has no problem on disk based block device, but has problems on ram based >>> block device, since we can't free memory used for data block. To overcome >>> this disadvantage, there is REQ_DISCARD functionality. If block device >>> support REQ_DISCARD and filesystem is mounted with discard option, >>> filesystem sends REQ_DISCARD to block device whenever some data blocks are >>> discarded. All we have to do is to handle this request. >>> >>> This patch implements to flag up QUEUE_FLAG_DISCARD and handle this >>> REQ_DISCARD request. With it, we can free memory used by zram if it isn't >>> used. >>> >>> Signed-off-by: Joonsoo Kim >>> --- >>> This patch is based on master branch of linux-next tree. >>> >>> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c >>> index 5ec61be..cff2c0e 100644 >>> --- a/drivers/block/zram/zram_drv.c >>> +++ b/drivers/block/zram/zram_drv.c >>> @@ -501,6 +501,20 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, >>> return ret; >>> } >>> >>> +static void zram_bio_discard(struct zram *zram, struct bio *bio) >>> +{ >>> + u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT; >> >> Hi Joonsoo, >> >> If bi_sector is not aligned on a page size, we might end up discarding >> a page that still contain valid data. >> >> > > Hello, Jerome. > > Is it possible that request isn't aligned on a page size if > logical/physical block size > is PAGE_SIZE? Yes, zram has an logical block size of 4k (ZRAM_LOGICAL_BLOCK_SIZE), while its physical block size, which is a page size, can be bigger. > When I tested it, I didn't find any invalid io. > If we meet any misaligned request, it would be filtered by > valid_io_request(). :) zram accepts request aligned on logical blocks. So valid_io_request() wouldn't filter misaligned requests out as long as they are aligned on logical blocks. If your system use 4k pages, your tests would never trigger the issue, but on a system which uses 64k pages, it could. Jerome > > Thanks. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/