[PATCH v3] mm: remove compressed copy from zram in-memory

[PATCH v3] mm: remove compressed copy from zram in-memory

[Minchan Kim]

Swap subsystem does lazy swap slot free with expecting the page
would be swapped out again so we can avoid unnecessary write.

But the problem in in-memory swap(ex, zram) is that it consumes
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,
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
be written out the swap device to reclaim it.
It means we never lose it.

I tested this patch with kernel compile workload.

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@google.com>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Konrad Rzeszutek Wilk <konrad@darnok.org>
Cc: Shaohua Li <shli@kernel.org>
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 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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Re: [PATCH v3] mm: remove compressed copy from zram in-memory

[Konrad Rzeszutek Wilk]

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@google.com>
> Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Konrad Rzeszutek Wilk <konrad@darnok.org>
> Cc: Shaohua Li <shli@kernel.org>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  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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Re: [PATCH v3] mm: remove compressed copy from zram in-memory

[Minchan Kim]

Hi Konrad,

On Thu, May 09, 2013 at 04:15:42PM -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, May 09, 2013 at 08:41:57AM +0900, Minchan Kim wrote:
> 
> Hey Michan,
        ^-n

It's a only thing I can know better than other native speakers. :)

 
> 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

Thanks for the correct whole sentence!
But Andrew alreay correted it with his style.
Although he was done, I'm giving a million thanks to you.
Surely, Thanks Andrew, too.

-- 
Kind regards,
Minchan Kim

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Re: [PATCH v3] mm: remove compressed copy from zram in-memory

[Konrad Rzeszutek Wilk]

On Fri, May 10, 2013 at 4:44 AM, Minchan Kim <minchan@kernel.org> wrote:
> Hi Konrad,
>
> On Thu, May 09, 2013 at 04:15:42PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Thu, May 09, 2013 at 08:41:57AM +0900, Minchan Kim wrote:
>>
>> Hey Michan,
>         ^-n
>
> It's a only thing I can know better than other native speakers. :)

I keep on misspelling your name. I am really sorry about that.

>
>
>> 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
>
> Thanks for the correct whole sentence!
> But Andrew alreay correted it with his style.

<nods> I saw his email a couple of hours ago.

> Although he was done, I'm giving a million thanks to you.
> Surely, Thanks Andrew, too.
>
> --
> Kind regards,
> Minchan Kim
>

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