Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751594AbaBZOGr (ORCPT ); Wed, 26 Feb 2014 09:06:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56393 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750943AbaBZOGq (ORCPT ); Wed, 26 Feb 2014 09:06:46 -0500 Message-ID: <530DF4EB.90605@redhat.com> Date: Wed, 26 Feb 2014 15:06:35 +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> <530DEFA7.5060103@redhat.com> <20140226135741.GB2217@swordfish.minsk.epam.com> In-Reply-To: <20140226135741.GB2217@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 02:57 PM, Sergey Senozhatsky wrote: > On (02/26/14 14:44), Jerome Marchand wrote: >> 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? >> > > it doesn't. cleanup patch 'do not pass rw argument to __zram_make_request()' > is in linux-next. > You're right. I must be blind since there is an exemple of __zram_make_request() without this argument just a few line below. > -ss > >> 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) I need to open my eyes. Jerome >>>> 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/