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Date: Mon, 22 Sep 2014 13:41:09 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Minchan Kim <minchan@...nel.org> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Hugh Dickins <hughd@...gle.com>, Shaohua Li <shli@...nel.org>, Jerome Marchand <jmarchan@...hat.com>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Dan Streetman <ddstreet@...e.org>, Nitin Gupta <ngupta@...are.org>, Luigi Semenzato <semenzato@...gle.com>, juno.choi@....com Subject: Re: [PATCH v1 1/5] zram: generalize swap_slot_free_notify On Mon, 22 Sep 2014 09:03:07 +0900 Minchan Kim <minchan@...nel.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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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