Messages in this thread | | | Date | Mon, 22 Sep 2014 13:41:09 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v1 1/5] zram: generalize swap_slot_free_notify |
| |
On Mon, 22 Sep 2014 09:03:07 +0900 Minchan Kim <minchan@kernel.org> wrote:
> Currently, swap_slot_free_notify is used for zram to free > duplicated copy page for memory efficiency when it knows > there is no reference to the swap slot. > > This patch generalizes it to be able to use for other > swap hint to communicate with VM. >
I really think we need to do a better job of documenting the code.
> index 94d93b1f8b53..c262bfbeafa9 100644 > --- a/Documentation/filesystems/Locking > +++ b/Documentation/filesystems/Locking > @@ -405,7 +405,7 @@ prototypes: > void (*unlock_native_capacity) (struct gendisk *); > int (*revalidate_disk) (struct gendisk *); > int (*getgeo)(struct block_device *, struct hd_geometry *); > - void (*swap_slot_free_notify) (struct block_device *, unsigned long); > + int (*swap_hint) (struct block_device *, unsigned int, void *); > > locking rules: > bd_mutex > @@ -418,7 +418,7 @@ media_changed: no > unlock_native_capacity: no > revalidate_disk: no > getgeo: no > -swap_slot_free_notify: no (see below) > +swap_hint: no (see below)
This didn't tell anyone anythnig much.
> index d78b245bae06..22a37764c409 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -926,7 +926,8 @@ error: > bio_io_error(bio); > } > > -static void zram_slot_free_notify(struct block_device *bdev, > +/* this callback is with swap_lock and sometimes page table lock held */
OK, that was useful.
It's called "page_table_lock".
Also *which* page_table_lock? current->mm?
> +static int zram_slot_free_notify(struct block_device *bdev, > unsigned long index) > { > struct zram *zram; > > ... > > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -1609,6 +1609,10 @@ static inline bool blk_integrity_is_initialized(struct gendisk *g) > > #endif /* CONFIG_BLK_DEV_INTEGRITY */ > > +enum swap_blk_hint { > + SWAP_FREE, > +};
This would be a great place to document SWAP_FREE.
> struct block_device_operations { > int (*open) (struct block_device *, fmode_t); > void (*release) (struct gendisk *, fmode_t); > @@ -1624,8 +1628,7 @@ struct block_device_operations { > void (*unlock_native_capacity) (struct gendisk *); > int (*revalidate_disk) (struct gendisk *); > int (*getgeo)(struct block_device *, struct hd_geometry *); > - /* this callback is with swap_lock and sometimes page table lock held */ > - void (*swap_slot_free_notify) (struct block_device *, unsigned long); > + int (*swap_hint)(struct block_device *, unsigned int, void *);
And this would be a suitable place to document ->swap_hint().
- Hint from who to who? Is it the caller providing the callee a hint or is the caller asking the callee for a hint?
- What is the meaning of the return value?
- What are the meaning of the arguments?
Please don't omit the argument names like this. They are useful! How is a reader to know what that "unsigned int" and "void *" actually *do*?
The second arg-which-doesn't-have-a-name should have had type swap_blk_hint, yes?
swap_blk_hint should be called swap_block_hint. I assume that's what "blk" means. Why does the name have "block" in there anyway? It has something to do with disk blocks? How is anyone supposed to work that out?
->swap_hint was converted to return an `int', but all the callers simply ignore the return value.
| |