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Message-ID: <20220930195215.2360317-1-bgeffon@google.com> Date: Fri, 30 Sep 2022 15:52:15 -0400 From: Brian Geffon <bgeffon@...gle.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, linux-kernel@...r.kernel.org, Suleiman Souhlal <suleiman@...gle.com>, Rom Lemarchand <romlem@...gle.com>, linux-mm@...ck.org, Brian Geffon <bgeffon@...gle.com> Subject: [PATCH] zram: Always expose rw_page Currently zram will adjust its fops to a version which does not contain rw_page when a backing device has been assigned. This is done to prevent upper layers from assuming a synchronous operation when a page may have been written back. This forces every operation through bio which has overhead associated with bio_alloc/frees. The code can be simplified to always expose a rw_page method and only in the rare event that a page is written back we instead will return -EOPNOTSUPP forcing the upper layer to fallback to bio. Signed-off-by: Brian Geffon <bgeffon@...gle.com> --- drivers/block/zram/zram_drv.c | 26 +++----------------------- 1 file changed, 3 insertions(+), 23 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 226ea76cc819..b9646886be0f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -52,9 +52,6 @@ static unsigned int num_devices = 1; static size_t huge_class_size; static const struct block_device_operations zram_devops; -#ifdef CONFIG_ZRAM_WRITEBACK -static const struct block_device_operations zram_wb_devops; -#endif static void zram_free_page(struct zram *zram, size_t index); static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec, @@ -543,17 +540,6 @@ static ssize_t backing_dev_store(struct device *dev, zram->backing_dev = backing_dev; zram->bitmap = bitmap; zram->nr_pages = nr_pages; - /* - * With writeback feature, zram does asynchronous IO so it's no longer - * synchronous device so let's remove synchronous io flag. Othewise, - * upper layer(e.g., swap) could wait IO completion rather than - * (submit and return), which will cause system sluggish. - * Furthermore, when the IO function returns(e.g., swap_readpage), - * upper layer expects IO was done so it could deallocate the page - * freely but in fact, IO is going on so finally could cause - * use-after-free when the IO is really done. - */ - zram->disk->fops = &zram_wb_devops; up_write(&zram->init_lock); pr_info("setup backing device %s\n", file_name); @@ -1267,6 +1253,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index, struct bio_vec bvec; zram_slot_unlock(zram, index); + /* If we don't have a bio we came via rw_page, we must fallback to bio */ + if (!bio) + return -EOPNOTSUPP; bvec.bv_page = page; bvec.bv_len = PAGE_SIZE; @@ -1848,15 +1837,6 @@ static const struct block_device_operations zram_devops = { .owner = THIS_MODULE }; -#ifdef CONFIG_ZRAM_WRITEBACK -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 -}; -#endif - static DEVICE_ATTR_WO(compact); static DEVICE_ATTR_RW(disksize); static DEVICE_ATTR_RO(initstate); -- 2.38.0.rc1.362.ged0d419d3c-goog
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