Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753221AbaBXQHY (ORCPT ); Mon, 24 Feb 2014 11:07:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52522 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752489AbaBXQHX (ORCPT ); Mon, 24 Feb 2014 11:07:23 -0500 Message-ID: <530B6E1F.1090608@redhat.com> Date: Mon, 24 Feb 2014 17:06:55 +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> <530B621E.9010309@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 04:56 PM, Joonsoo Kim wrote: > 2014-02-25 0:15 GMT+09:00 Jerome Marchand : >> 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. > > Okay. I got it. > So, how about using PAGE_SIZE as ZRAM_LOGICAL_BLOCK_SIZE? > Is there any reason to set 4096 to ZRAM_LOGICAL_BLOCK_SIZE, > instead of setting PAGE_SIZE to ZRAM_LOGICAL_BLOCK_SIZE? > ZRAM_LOGICAL_BLOCK_SIZE was introduced in commit 7b19b8d because the block layer couldn't handle 64k logical block. Also, some filesytems (including FAT IRC), can't cope with 64k block either. > 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/