On Thu, May 09, 2013 at 08:41:57AM +0900, Minchan Kim wrote:
Hey Michan,
Just a couple of syntax corrections. The code comment could also
benefit from this.
Otherwise it looks OK to me.
> Swap subsystem does lazy swap slot free with expecting the page
^-a ^- the expectation that
> would be swapped out again so we can avoid unnecessary write.
^--that it
>
> But the problem in in-memory swap(ex, zram) is that it consumes
^^-with
> memory space until vm_swap_full(ie, used half of all of swap device)
> condition meet. It could be bad if we use multiple swap device,
^- 'is' ^^^^^ - 'would' ^^^^^-devices
> small in-memory swap and big storage swap or in-memory swap alone.
^-, ^-,
>
> This patch makes swap subsystem free swap slot as soon as swap-read
> is completed and make the swapcache page dirty so the page should
^-makes ^-'that the'
> be written out the swap device to reclaim it.
> It means we never lose it.
>
> I tested this patch with kernel compile workload.
^-a
>
> 1. before
>
> compile time : 9882.42
> zram max wasted space by fragmentation: 13471881 byte
> memory space consumed by zram: 174227456 byte
> the number of slot free notify: 206684
>
> 2. after
>
> compile time : 9653.90
> zram max wasted space by fragmentation: 11805932 byte
> memory space consumed by zram: 154001408 byte
> the number of slot free notify: 426972
>
> * changelog from v3
> * Rebased on next-20130508
>
> * changelog from v1
> * Add more comment
>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
> Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/page_io.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/mm/page_io.c b/mm/page_io.c
> index a294076..527db57 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -21,6 +21,7 @@
> #include <linux/writeback.h>
> #include <linux/frontswap.h>
> #include <linux/aio.h>
> +#include <linux/blkdev.h>
> #include <asm/pgtable.h>
>
> static struct bio *get_swap_bio(gfp_t gfp_flags,
> @@ -82,8 +83,42 @@ void end_swap_bio_read(struct bio *bio, int err, struct batch_complete *batch)
> iminor(bio->bi_bdev->bd_inode),
> (unsigned long long)bio->bi_sector);
> } else {
> + struct swap_info_struct *sis;
> +
> SetPageUptodate(page);
> + sis = page_swap_info(page);
> + if (sis->flags & SWP_BLKDEV) {
> + /*
> + * Swap subsystem does lazy swap slot free with
> + * expecting the page would be swapped out again
> + * so we can avoid unnecessary write if the page
> + * isn't redirty.
> + * It's good for real swap storage because we can
> + * reduce unnecessary I/O and enhance wear-leveling
> + * if you use SSD as swap device.
> + * But if you use in-memory swap device(ex, zram),
> + * it causes duplicated copy between uncompressed
> + * data in VM-owned memory and compressed data in
> + * zram-owned memory. So let's free zram-owned memory
> + * and make the VM-owned decompressed page *dirty*
> + * so the page should be swap out somewhere again if
> + * we want to reclaim it, again.
> + */
> + struct gendisk *disk = sis->bdev->bd_disk;
> + if (disk->fops->swap_slot_free_notify) {
> + swp_entry_t entry;
> + unsigned long offset;
> +
> + entry.val = page_private(page);
> + offset = swp_offset(entry);
> +
> + SetPageDirty(page);
> + disk->fops->swap_slot_free_notify(sis->bdev,
> + offset);
> + }
> + }
> }
> +
> unlock_page(page);
> bio_put(bio);
> }
> --
> 1.8.2.1
>
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