| Message ID | 20220930195215.2360317-1-bgeffon@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | zram: Always expose rw_page | expand |
On (22/09/30 15:52), Brian Geffon wrote: > 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. Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org> > @@ -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; The comment is above 80 cols.
On Sun, Oct 2, 2022 at 10:59 PM Sergey Senozhatsky <senozhatsky@chromium.org> wrote: > > On (22/09/30 15:52), Brian Geffon wrote: > > 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. > > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org> Thank you. > > > @@ -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; > > The comment is above 80 cols. Fixed in a new patch.
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);
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@google.com> --- drivers/block/zram/zram_drv.c | 26 +++----------------------- 1 file changed, 3 insertions(+), 23 deletions(-)