Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752333AbaBZNoT (ORCPT ); Wed, 26 Feb 2014 08:44:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47109 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750717AbaBZNoS (ORCPT ); Wed, 26 Feb 2014 08:44:18 -0500 Message-ID: <530DEFA7.5060103@redhat.com> Date: Wed, 26 Feb 2014 14:44:07 +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: Sergey Senozhatsky CC: Joonsoo Kim , Andrew Morton , Minchan Kim , Nitin Gupta , linux-kernel@vger.kernel.org, Joonsoo Kim Subject: Re: [PATCH v2] zram: support REQ_DISCARD References: <1393392195-20743-1-git-send-email-iamjoonsoo.kim@lge.com> <20140226131625.GA2217@swordfish.minsk.epam.com> In-Reply-To: <20140226131625.GA2217@swordfish.minsk.epam.com> 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 02/26/2014 02:16 PM, Sergey Senozhatsky wrote: > Hello, > > On (02/26/14 14:23), 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; >> + 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; >> + } >> +} >> + > > a side note, do we need zram_bio_discard() function? I mean, can we handle > discard request in zram_bvec_rw(), where we already know index, etc. (passed > from __zram_make_request())? > We'd still have to make sure not to discard pages that are still partially used, but it might simplify the code: __zram_make_request() already takes care of splitting the request. > for example: > > @@ -510,6 +510,11 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, > ret = zram_bvec_write(zram, bvec, index, offset); > } > > + if (unlikely(bio->bi_rw & REQ_DISCARD)) { + if (!is_partial_io(bvec) { > + write_lock(&zram->meta->tb_lock); > + zram_free_page(zram, index); > + write_unlock(&zram->meta->tb_lock); + } Also this code might still call zram_bvec_read() and increase num_reads for discard request: I guess bio_data_dir(bio) == READ == 0 in this case. Btw, why __zram_make_request() has an that rw argument? All the information it needs is passed by the bio argument already. I kind of recollect to have seen a cleanup patch that get rid of it or is it just my imagination? Jerome > + } > return ret; > } > > -ss > >> 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; >> + queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue); >> >> add_disk(zram->disk); >> >> -- >> 1.7.9.5 >> -- 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/