Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752635AbaB1PYj (ORCPT ); Fri, 28 Feb 2014 10:24:39 -0500 Received: from mail-we0-f176.google.com ([74.125.82.176]:63823 "EHLO mail-we0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752285AbaB1PYi (ORCPT ); Fri, 28 Feb 2014 10:24:38 -0500 MIME-Version: 1.0 In-Reply-To: <20140226080732.GF4606@bbox> References: <1393392195-20743-1-git-send-email-iamjoonsoo.kim@lge.com> <20140226080732.GF4606@bbox> Date: Sat, 1 Mar 2014 00:24:37 +0900 Message-ID: Subject: Re: [PATCH v2] zram: support REQ_DISCARD From: Joonsoo Kim To: Minchan Kim Cc: Joonsoo Kim , Andrew Morton , Nitin Gupta , LKML , Sergey Senozhatsky , Jerome Marchand Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-02-26 17:07 GMT+09:00 Minchan Kim : > Hi Joonsoo, > > On Wed, Feb 26, 2014 at 02:23:15PM +0900, 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. >> >> v2: handle unaligned case commented by Jerome >> >> Signed-off-by: Joonsoo Kim >> >> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c >> index 5ec61be..5364c1e 100644 >> --- a/drivers/block/zram/zram_drv.c >> +++ b/drivers/block/zram/zram_drv.c >> @@ -501,6 +501,36 @@ 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; >> + size_t n = bio->bi_iter.bi_size; > > Nitpick: > Please use more meaningful name(ex, len) rather than 'n'. > Hello, Minchan. Will do. >> + size_t misalign; >> + >> + * On some arch, logical block (4096) aligned request couldn't be >> + * aligned to PAGE_SIZE, since their PAGE_SIZE aren't 4096. >> + * Therefore we should handle this misaligned case here. >> + */ >> + misalign = (bio->bi_iter.bi_sector & >> + (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT; >> + if (misalign) { >> + if (n < misalign) >> + return; >> + >> + n -= misalign; >> + index++; >> + } >> + >> + while (n >= PAGE_SIZE) { >> + write_lock(&zram->meta->tb_lock); >> + zram_free_page(zram, index); >> + write_unlock(&zram->meta->tb_lock); >> + index++; >> + n -= PAGE_SIZE; >> + } >> +} >> + >> static void zram_reset_device(struct zram *zram, bool reset_capacity) >> { >> size_t index; >> @@ -618,6 +648,12 @@ static void __zram_make_request(struct zram *zram, struct bio *bio) >> struct bio_vec bvec; >> struct bvec_iter iter; >> >> + if (unlikely(bio->bi_rw & REQ_DISCARD)) { >> + zram_bio_discard(zram, bio); >> + bio_endio(bio, 0); >> + return; >> + } >> + >> index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT; >> offset = (bio->bi_iter.bi_sector & >> (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT; >> @@ -784,6 +820,10 @@ static int create_device(struct zram *zram, int device_id) >> ZRAM_LOGICAL_BLOCK_SIZE); >> blk_queue_io_min(zram->disk->queue, PAGE_SIZE); >> blk_queue_io_opt(zram->disk->queue, PAGE_SIZE); >> + zram->disk->queue->limits.discard_granularity = PAGE_SIZE; >> + zram->disk->queue->limits.max_discard_sectors = UINT_MAX; >> + zram->disk->queue->limits.discard_zeroes_data = 1; > > I don't know what discard_zeroes_data does mean. It seems we should > make sure zram should return zero pages for discarded block on next > time but prolblem could happen if you bail out in discard logic > due to misalign but caller seem to know it was successful? > > What happens in this case? > This will result in the problem what you think about. I will change it like as following. if (PAGE_SIZE == ZRAM_LOGICAL_BLOCK_SIZE) zram->disk->queue->limits.discard_zeroes_data = 1; else zram->disk->queue->limits.discard_zeroes_data = 0; Does It work for you? 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/