[Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[changkun.li]

In zswap, store page A to zbud if the compression ratio is high, insert
its entry into rbtree. if there is a entry B which has the same offset
in the rbtree.Remove and free B before insert the entry of A.

case:
if the compression ratio of page A is not high, return without checking
the same offset one in rbtree.

if there is a entry B which has the same offset in the rbtree. Now, we
make sure B is invalid or expired. But the entry and compressed memory
of B are not freed in time.

Because zswap spaces data in memory, it makes the utilization of memory
lower. the other valid data in zbud is writeback to swap device more
possibility, when zswap is full.

So if we make sure a entry is expired, free it in time.

Signed-off-by: changkun.li<xfishcoder@gmail.com>
---
 mm/zswap.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index cbd9578..90a2813 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -596,6 +596,7 @@ fail:
 	return ret;
 }
 
+static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t
offset);
 /*********************************
 * frontswap hooks
 **********************************/
@@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,
pgoff_t offset,
 
 	if (!tree) {
 		ret = -ENODEV;
-		goto reject;
+		goto nodev;
 	}
 
 	/* reclaim space if needed */
@@ -695,6 +696,8 @@ freepage:
 	put_cpu_var(zswap_dstmem);
 	zswap_entry_cache_free(entry);
 reject:
+	zswap_frontswap_invalidate_page(type, offset);
+nodev:
 	return ret;
 }
 
-- 
1.7.1


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Re: [Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[Bob Liu]

On 11/08/2013 05:50 PM, changkun.li wrote:
> In zswap, store page A to zbud if the compression ratio is high, insert
> its entry into rbtree. if there is a entry B which has the same offset
> in the rbtree.Remove and free B before insert the entry of A.
> 
> case:
> if the compression ratio of page A is not high, return without checking
> the same offset one in rbtree.
> 
> if there is a entry B which has the same offset in the rbtree. Now, we
> make sure B is invalid or expired. But the entry and compressed memory
> of B are not freed in time.
> 
> Because zswap spaces data in memory, it makes the utilization of memory
> lower. the other valid data in zbud is writeback to swap device more
> possibility, when zswap is full.
> 
> So if we make sure a entry is expired, free it in time.
> 
> Signed-off-by: changkun.li<xfishcoder@gmail.com>
> ---
>  mm/zswap.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index cbd9578..90a2813 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -596,6 +596,7 @@ fail:
>  	return ret;
>  }
>  
> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t
> offset);
>  /*********************************
>  * frontswap hooks
>  **********************************/
> @@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,
> pgoff_t offset,
>  
>  	if (!tree) {
>  		ret = -ENODEV;
> -		goto reject;
> +		goto nodev;
>  	}
>  
>  	/* reclaim space if needed */
> @@ -695,6 +696,8 @@ freepage:
>  	put_cpu_var(zswap_dstmem);
>  	zswap_entry_cache_free(entry);
>  reject:
> +	zswap_frontswap_invalidate_page(type, offset);

I'm afraid when arrives here zswap_rb_search(offset) will always return
NULL entry. So most of the time, it's just waste time to call
zswap_frontswap_invalidate_page() to search rbtree.

-- 
Regards,
-Bob

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Re: [Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[changkun.li]

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I agree with you, I see the __frontswap_store in 'frontswap.c', it knows
the same offset entry exist in zswap. we could modify like this?:
int __frontswap_store(struct page *page)
{
    int ret = -1, dup = 0;
    swp_entry_t entry = { .val = page_private(page), };
    int type = swp_type(entry);
    struct swap_info_struct *sis = swap_info[type];
    pgoff_t offset = swp_offset(entry);

    /*
     * Return if no backend registed.
     * Don't need to inc frontswap_failed_stores here.
     */
    if (!frontswap_ops)
        return ret;

    BUG_ON(!PageLocked(page));
    BUG_ON(sis == NULL);
    if (__frontswap_test(sis, offset))
        dup = 1;
    ret = frontswap_ops->store(type, offset, page);
    if (ret == 0) {
        set_bit(offset, sis->frontswap_map);
        inc_frontswap_succ_stores();
        if (!dup)
            atomic_inc(&sis->frontswap_pages);
    } else {
        /*
          failed dup always results in automatic invalidate of
          the (older) page from frontswap
         */
        inc_frontswap_failed_stores();
++       if (dup) {
--         if (dup)
            __frontswap_clear(sis, offset);
++        __frontswap_invalidate_page(type, offset);
++       }
    }
    if (frontswap_writethrough_enabled)
        /* report failure so swap also writes to swap device */
        ret = -1;
    return ret;
}

but maybe the other frontswap modules is not space memory, they need not
call __frontswap_invalidate_page. so the code in here is only better for
zswap.



On Fri, Nov 8, 2013 at 6:28 PM, Bob Liu <bob.liu@oracle.com> wrote:

> On 11/08/2013 05:50 PM, changkun.li wrote:
> > In zswap, store page A to zbud if the compression ratio is high, insert
> > its entry into rbtree. if there is a entry B which has the same offset
> > in the rbtree.Remove and free B before insert the entry of A.
> >
> > case:
> > if the compression ratio of page A is not high, return without checking
> > the same offset one in rbtree.
> >
> > if there is a entry B which has the same offset in the rbtree. Now, we
> > make sure B is invalid or expired. But the entry and compressed memory
> > of B are not freed in time.
> >
> > Because zswap spaces data in memory, it makes the utilization of memory
> > lower. the other valid data in zbud is writeback to swap device more
> > possibility, when zswap is full.
> >
> > So if we make sure a entry is expired, free it in time.
> >
> > Signed-off-by: changkun.li<xfishcoder@gmail.com>
> > ---
> >  mm/zswap.c |    5 ++++-
> >  1 files changed, 4 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index cbd9578..90a2813 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -596,6 +596,7 @@ fail:
> >       return ret;
> >  }
> >
> > +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t
> > offset);
> >  /*********************************
> >  * frontswap hooks
> >  **********************************/
> > @@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,
> > pgoff_t offset,
> >
> >       if (!tree) {
> >               ret = -ENODEV;
> > -             goto reject;
> > +             goto nodev;
> >       }
> >
> >       /* reclaim space if needed */
> > @@ -695,6 +696,8 @@ freepage:
> >       put_cpu_var(zswap_dstmem);
> >       zswap_entry_cache_free(entry);
> >  reject:
> > +     zswap_frontswap_invalidate_page(type, offset);
>
> I'm afraid when arrives here zswap_rb_search(offset) will always return
> NULL entry. So most of the time, it's just waste time to call
> zswap_frontswap_invalidate_page() to search rbtree.
>
> --
> Regards,
> -Bob
>

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Re: [Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[Weijie Yang]

add cc Seth 's new email address.

On Fri, Nov 8, 2013 at 6:28 PM, Bob Liu <bob.liu@oracle.com> wrote:
> On 11/08/2013 05:50 PM, changkun.li wrote:
>> In zswap, store page A to zbud if the compression ratio is high, insert
>> its entry into rbtree. if there is a entry B which has the same offset
>> in the rbtree.Remove and free B before insert the entry of A.
>>
>> case:
>> if the compression ratio of page A is not high, return without checking
>> the same offset one in rbtree.
>>
>> if there is a entry B which has the same offset in the rbtree. Now, we
>> make sure B is invalid or expired. But the entry and compressed memory
>> of B are not freed in time.
>>
>> Because zswap spaces data in memory, it makes the utilization of memory
>> lower. the other valid data in zbud is writeback to swap device more
>> possibility, when zswap is full.
>>
>> So if we make sure a entry is expired, free it in time.
>>
>> Signed-off-by: changkun.li<xfishcoder@gmail.com>
>> ---
>>  mm/zswap.c |    5 ++++-
>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index cbd9578..90a2813 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -596,6 +596,7 @@ fail:
>>       return ret;
>>  }
>>
>> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t
>> offset);
>>  /*********************************
>>  * frontswap hooks
>>  **********************************/
>> @@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,
>> pgoff_t offset,
>>
>>       if (!tree) {
>>               ret = -ENODEV;
>> -             goto reject;
>> +             goto nodev;
>>       }
>>
>>       /* reclaim space if needed */
>> @@ -695,6 +696,8 @@ freepage:
>>       put_cpu_var(zswap_dstmem);
>>       zswap_entry_cache_free(entry);
>>  reject:
>> +     zswap_frontswap_invalidate_page(type, offset);
>
> I'm afraid when arrives here zswap_rb_search(offset) will always return
> NULL entry. So most of the time, it's just waste time to call
> zswap_frontswap_invalidate_page() to search rbtree.

Yes, it is a bug.

But I agree with Bob, this patch is not efficient.

How about like this?

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 1b24bdc..1227896
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
                  the (older) page from frontswap
                 */
                inc_frontswap_failed_stores();
-               if (dup)
+               if (dup) {
+                       frontswap_ops->invalidate_page(type, offset);
                        __frontswap_clear(sis, offset);
+               }
        }
        if (frontswap_writethrough_enabled)
                /* report failure so swap also writes to swap device */


> --
> Regards,
> -Bob
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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Re: [Patch 3.11.7 1/1]mm: remove and free expired data in time in zswap

[Weijie Yang]

Hi, Seth

Would you please check this issue?  Thanks

On Mon, Nov 18, 2013 at 3:06 PM, Weijie Yang <weijie.yang.kh@gmail.com> wrote:
> add cc Seth 's new email address.
>
> On Fri, Nov 8, 2013 at 6:28 PM, Bob Liu <bob.liu@oracle.com> wrote:
>> On 11/08/2013 05:50 PM, changkun.li wrote:
>>> In zswap, store page A to zbud if the compression ratio is high, insert
>>> its entry into rbtree. if there is a entry B which has the same offset
>>> in the rbtree.Remove and free B before insert the entry of A.
>>>
>>> case:
>>> if the compression ratio of page A is not high, return without checking
>>> the same offset one in rbtree.
>>>
>>> if there is a entry B which has the same offset in the rbtree. Now, we
>>> make sure B is invalid or expired. But the entry and compressed memory
>>> of B are not freed in time.
>>>
>>> Because zswap spaces data in memory, it makes the utilization of memory
>>> lower. the other valid data in zbud is writeback to swap device more
>>> possibility, when zswap is full.
>>>
>>> So if we make sure a entry is expired, free it in time.
>>>
>>> Signed-off-by: changkun.li<xfishcoder@gmail.com>
>>> ---
>>>  mm/zswap.c |    5 ++++-
>>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/mm/zswap.c b/mm/zswap.c
>>> index cbd9578..90a2813 100644
>>> --- a/mm/zswap.c
>>> +++ b/mm/zswap.c
>>> @@ -596,6 +596,7 @@ fail:
>>>       return ret;
>>>  }
>>>
>>> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t
>>> offset);
>>>  /*********************************
>>>  * frontswap hooks
>>>  **********************************/
>>> @@ -614,7 +615,7 @@ static int zswap_frontswap_store(unsigned type,
>>> pgoff_t offset,
>>>
>>>       if (!tree) {
>>>               ret = -ENODEV;
>>> -             goto reject;
>>> +             goto nodev;
>>>       }
>>>
>>>       /* reclaim space if needed */
>>> @@ -695,6 +696,8 @@ freepage:
>>>       put_cpu_var(zswap_dstmem);
>>>       zswap_entry_cache_free(entry);
>>>  reject:
>>> +     zswap_frontswap_invalidate_page(type, offset);
>>
>> I'm afraid when arrives here zswap_rb_search(offset) will always return
>> NULL entry. So most of the time, it's just waste time to call
>> zswap_frontswap_invalidate_page() to search rbtree.
>
> Yes, it is a bug.
>
> But I agree with Bob, this patch is not efficient.
>
> How about like this?
>
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> index 1b24bdc..1227896
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
>                   the (older) page from frontswap
>                  */
>                 inc_frontswap_failed_stores();
> -               if (dup)
> +               if (dup) {
> +                       frontswap_ops->invalidate_page(type, offset);
>                         __frontswap_clear(sis, offset);
> +               }
>         }
>         if (frontswap_writethrough_enabled)
>                 /* report failure so swap also writes to swap device */
>
>
>> --
>> Regards,
>> -Bob
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.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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