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Sun, 26 Jul 2020 12:06:41 -0700 (PDT) Date: Sun, 26 Jul 2020 12:06:39 -0700 From: Minchan Kim To: Christoph Hellwig Cc: Jens Axboe , Song Liu , Hans de Goede , Richard Weinberger , linux-mtd@lists.infradead.org, dm-devel@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, drbd-dev@lists.linbit.com, linux-raid@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org Subject: Re: [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Message-ID: <20200726190639.GA560221@google.com> References: <20200726150333.305527-1-hch@lst.de> <20200726150333.305527-11-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200726150333.305527-11-hch@lst.de> X-Rspamd-Queue-Id: 9D0D818038E60 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Jul 26, 2020 at 05:03:29PM +0200, Christoph Hellwig wrote: > BDI_CAP_SYNCHRONOUS_IO is only checked in the swap code, and used to > decided if ->rw_page can be used on a block device. Just check up for > the method instead. The only complication is that zram needs a second > set of block_device_operations as it can switch between modes that > actually support ->rw_page and those who don't. > > Signed-off-by: Christoph Hellwig > --- > drivers/block/brd.c | 1 - > drivers/block/zram/zram_drv.c | 19 +++++++++++++------ > drivers/nvdimm/btt.c | 2 -- > drivers/nvdimm/pmem.c | 1 - > include/linux/backing-dev.h | 9 --------- > mm/swapfile.c | 2 +- > 6 files changed, 14 insertions(+), 20 deletions(-) > > diff --git a/drivers/block/brd.c b/drivers/block/brd.c > index 2723a70eb85593..cc49a921339f77 100644 > --- a/drivers/block/brd.c > +++ b/drivers/block/brd.c > @@ -403,7 +403,6 @@ static struct brd_device *brd_alloc(int i) > disk->flags = GENHD_FL_EXT_DEVT; > sprintf(disk->disk_name, "ram%d", i); > set_capacity(disk, rd_size * 2); > - brd->brd_queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO; > > /* Tell the block layer that this is not a rotational device */ > blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue); > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 9100ac36670afc..d73ddf018fa65f 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -52,6 +52,9 @@ static unsigned int num_devices = 1; > */ > static size_t huge_class_size; > > +static const struct block_device_operations zram_devops; > +static const struct block_device_operations zram_wb_devops; > + > static void zram_free_page(struct zram *zram, size_t index); > static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec, > u32 index, int offset, struct bio *bio); > @@ -408,8 +411,7 @@ static void reset_bdev(struct zram *zram) > zram->backing_dev = NULL; > zram->old_block_size = 0; > zram->bdev = NULL; > - zram->disk->queue->backing_dev_info->capabilities |= > - BDI_CAP_SYNCHRONOUS_IO; > + zram->disk->fops = &zram_devops; > kvfree(zram->bitmap); > zram->bitmap = NULL; > } > @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev, > * freely but in fact, IO is going on so finally could cause > * use-after-free when the IO is really done. > */ > - zram->disk->queue->backing_dev_info->capabilities &= > - ~BDI_CAP_SYNCHRONOUS_IO; > + zram->disk->fops = &zram_wb_devops; > up_write(&zram->init_lock); For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page every time on read/write path. This one with next patch will make zram use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO, which introduce regression for performance. In the swap code, BDI_CAP_SYNCHRONOUS_IO is used to avoid swap cache when the page was private. bdev_read_page is not designed to rely on synchronous operation. That's why this patch breaks the old behavior. > > pr_info("setup backing device %s\n", file_name); > @@ -1819,6 +1820,13 @@ static const struct block_device_operations zram_devops = { > .owner = THIS_MODULE > }; > > +static const struct block_device_operations zram_wb_devops = { > + .open = zram_open, > + .submit_bio = zram_submit_bio, > + .swap_slot_free_notify = zram_slot_free_notify, > + .owner = THIS_MODULE > +}; > + > static DEVICE_ATTR_WO(compact); > static DEVICE_ATTR_RW(disksize); > static DEVICE_ATTR_RO(initstate); > @@ -1946,8 +1954,7 @@ static int zram_add(void) > if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE) > blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX); > > - zram->disk->queue->backing_dev_info->capabilities |= > - (BDI_CAP_STABLE_WRITES | BDI_CAP_SYNCHRONOUS_IO); > + zram->disk->queue->backing_dev_info->capabilities |= BDI_CAP_STABLE_WRITES; > device_add_disk(NULL, zram->disk, zram_disk_attr_groups); > > strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor)); > diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c > index 412d21d8f64351..b4184dc9b41eb4 100644 > --- a/drivers/nvdimm/btt.c > +++ b/drivers/nvdimm/btt.c > @@ -1540,8 +1540,6 @@ static int btt_blk_init(struct btt *btt) > btt->btt_disk->private_data = btt; > btt->btt_disk->queue = btt->btt_queue; > btt->btt_disk->flags = GENHD_FL_EXT_DEVT; > - btt->btt_disk->queue->backing_dev_info->capabilities |= > - BDI_CAP_SYNCHRONOUS_IO; > > blk_queue_logical_block_size(btt->btt_queue, btt->sector_size); > blk_queue_max_hw_sectors(btt->btt_queue, UINT_MAX); > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c > index 94790e6e0e4ce1..436b83fb24ad61 100644 > --- a/drivers/nvdimm/pmem.c > +++ b/drivers/nvdimm/pmem.c > @@ -478,7 +478,6 @@ static int pmem_attach_disk(struct device *dev, > disk->queue = q; > disk->flags = GENHD_FL_EXT_DEVT; > disk->private_data = pmem; > - disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO; > nvdimm_namespace_disk_name(ndns, disk->disk_name); > set_capacity(disk, (pmem->size - pmem->pfn_pad - pmem->data_offset) > / 512); > diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h > index 52583b6f2ea05d..860ea33571bce5 100644 > --- a/include/linux/backing-dev.h > +++ b/include/linux/backing-dev.h > @@ -122,9 +122,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio); > * BDI_CAP_NO_WRITEBACK: Don't write pages back > * BDI_CAP_NO_ACCT_WB: Don't automatically account writeback pages > * BDI_CAP_STRICTLIMIT: Keep number of dirty pages below bdi threshold. > - * > - * BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be > - * inefficient. > */ > #define BDI_CAP_NO_ACCT_DIRTY 0x00000001 > #define BDI_CAP_NO_WRITEBACK 0x00000002 > @@ -132,7 +129,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio); > #define BDI_CAP_STABLE_WRITES 0x00000008 > #define BDI_CAP_STRICTLIMIT 0x00000010 > #define BDI_CAP_CGROUP_WRITEBACK 0x00000020 > -#define BDI_CAP_SYNCHRONOUS_IO 0x00000040 > > #define BDI_CAP_NO_ACCT_AND_WRITEBACK \ > (BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB) > @@ -174,11 +170,6 @@ static inline int wb_congested(struct bdi_writeback *wb, int cong_bits) > long congestion_wait(int sync, long timeout); > long wait_iff_congested(int sync, long timeout); > > -static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi) > -{ > - return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO; > -} > - > static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi) > { > return bdi->capabilities & BDI_CAP_STABLE_WRITES; > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 6c26916e95fd4a..18eac97b10e502 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3230,7 +3230,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > if (bdi_cap_stable_pages_required(inode_to_bdi(inode))) > p->flags |= SWP_STABLE_WRITES; > > - if (bdi_cap_synchronous_io(inode_to_bdi(inode))) > + if (p->bdev && p->bdev->bd_disk->fops->rw_page) > p->flags |= SWP_SYNCHRONOUS_IO; > > if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) { > -- > 2.27.0 >