[PATCH] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[PATCH] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Hui Zhu]

After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
can handle the ZS_EMPTY zspage.

But it will affect the free_work free the zspage.  That will make this
ZS_EMPTY zspage stay in system until another zspage wake up free_work.

Make this patch let zs_page_migrate wake up free_work if need.

Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
---
 mm/zsmalloc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 62457eb..48ce043 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -2035,8 +2035,14 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 	 * Page migration is done so let's putback isolated zspage to
 	 * the list if @page is final isolated subpage in the zspage.
 	 */
-	if (!is_zspage_isolated(zspage))
-		putback_zspage(class, zspage);
+	if (!is_zspage_isolated(zspage)) {
+		/*
+		 * The page and class is locked, we cannot free zspage
+		 * immediately so let's defer.
+		 */
+		if (putback_zspage(class, zspage) == ZS_EMPTY)
+			schedule_work(&pool->free_work);
+	}
 
 	reset_page(page);
 	put_page(page);
-- 
1.9.1

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Re: [PATCH] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Minchan Kim]

Hi Hui,

On Mon, Aug 14, 2017 at 02:34:46PM +0800, Hui Zhu wrote:
> After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
> loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
> can handle the ZS_EMPTY zspage.
> 
> But it will affect the free_work free the zspage.  That will make this
> ZS_EMPTY zspage stay in system until another zspage wake up free_work.
> 
> Make this patch let zs_page_migrate wake up free_work if need.
> 
> Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>

This patch makes me remind why I didn't try to migrate empty zspage
as you did e2846124f9a2. I have forgotten it toally.

We cannot guarantee when the freeing of the page happens if we use
deferred freeing in zs_page_migrate. However, we returns
MIGRATEPAGE_SUCCESS which is totally lie.
Without instant freeing the page, it doesn't help the migration
situation. No?

I start to wonder why your patch e2846124f9a2 helped your test.
I will think over the issue with fresh mind after the holiday.

> ---
>  mm/zsmalloc.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 62457eb..48ce043 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -2035,8 +2035,14 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>  	 * Page migration is done so let's putback isolated zspage to
>  	 * the list if @page is final isolated subpage in the zspage.
>  	 */
> -	if (!is_zspage_isolated(zspage))
> -		putback_zspage(class, zspage);
> +	if (!is_zspage_isolated(zspage)) {
> +		/*
> +		 * The page and class is locked, we cannot free zspage
> +		 * immediately so let's defer.
> +		 */
> +		if (putback_zspage(class, zspage) == ZS_EMPTY)
> +			schedule_work(&pool->free_work);
> +	}
>  
>  	reset_page(page);
>  	put_page(page);
> -- 
> 1.9.1
> 
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Re: [PATCH] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Hui Zhu]

2017-08-14 16:31 GMT+08:00 Minchan Kim <minchan@kernel.org>:
> Hi Hui,
>
> On Mon, Aug 14, 2017 at 02:34:46PM +0800, Hui Zhu wrote:
>> After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
>> loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
>> can handle the ZS_EMPTY zspage.
>>
>> But it will affect the free_work free the zspage.  That will make this
>> ZS_EMPTY zspage stay in system until another zspage wake up free_work.
>>
>> Make this patch let zs_page_migrate wake up free_work if need.
>>
>> Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
>> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
>
> This patch makes me remind why I didn't try to migrate empty zspage
> as you did e2846124f9a2. I have forgotten it toally.
>
> We cannot guarantee when the freeing of the page happens if we use
> deferred freeing in zs_page_migrate. However, we returns
> MIGRATEPAGE_SUCCESS which is totally lie.
> Without instant freeing the page, it doesn't help the migration
> situation. No?
>

Sorry I think the reason is I didn't introduce this clear.
After I patch e2846124f9a2.  I got some false in zs_page_isolate:
if (get_zspage_inuse(zspage) == 0) {
spin_unlock(&class->lock);
return false;
}
The page of this zspage was migrated in before.

So I think e2846124f9a2 is OK that MIGRATEPAGE_SUCCESS with the "page".
But it keep the "newpage" with a empty zspage inside system.
Root cause is zs_page_isolate remove it from  ZS_EMPTY list but not
call zs_page_putback "schedule_work(&pool->free_work);".  Because
zs_page_migrate done the job without
"schedule_work(&pool->free_work);"

That is why I made the new patch.

Thanks,
Hui

> I start to wonder why your patch e2846124f9a2 helped your test.
> I will think over the issue with fresh mind after the holiday.
>
>> ---
>>  mm/zsmalloc.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index 62457eb..48ce043 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -2035,8 +2035,14 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>>        * Page migration is done so let's putback isolated zspage to
>>        * the list if @page is final isolated subpage in the zspage.
>>        */
>> -     if (!is_zspage_isolated(zspage))
>> -             putback_zspage(class, zspage);
>> +     if (!is_zspage_isolated(zspage)) {
>> +             /*
>> +              * The page and class is locked, we cannot free zspage
>> +              * immediately so let's defer.
>> +              */
>> +             if (putback_zspage(class, zspage) == ZS_EMPTY)
>> +                     schedule_work(&pool->free_work);
>> +     }
>>
>>       reset_page(page);
>>       put_page(page);
>> --
>> 1.9.1
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
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Re: [PATCH] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Minchan Kim]

On Mon, Aug 14, 2017 at 05:11:50PM +0800, Hui Zhu wrote:
> 2017-08-14 16:31 GMT+08:00 Minchan Kim <minchan@kernel.org>:
> > Hi Hui,
> >
> > On Mon, Aug 14, 2017 at 02:34:46PM +0800, Hui Zhu wrote:
> >> After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
> >> loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
> >> can handle the ZS_EMPTY zspage.
> >>
> >> But it will affect the free_work free the zspage.  That will make this
> >> ZS_EMPTY zspage stay in system until another zspage wake up free_work.
> >>
> >> Make this patch let zs_page_migrate wake up free_work if need.
> >>
> >> Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
> >> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
> >
> > This patch makes me remind why I didn't try to migrate empty zspage
> > as you did e2846124f9a2. I have forgotten it toally.
> >
> > We cannot guarantee when the freeing of the page happens if we use
> > deferred freeing in zs_page_migrate. However, we returns
> > MIGRATEPAGE_SUCCESS which is totally lie.
> > Without instant freeing the page, it doesn't help the migration
> > situation. No?
> >
> 
> Sorry I think the reason is I didn't introduce this clear.
> After I patch e2846124f9a2.  I got some false in zs_page_isolate:
> if (get_zspage_inuse(zspage) == 0) {
> spin_unlock(&class->lock);
> return false;
> }
> The page of this zspage was migrated in before.
> 
> So I think e2846124f9a2 is OK that MIGRATEPAGE_SUCCESS with the "page".
> But it keep the "newpage" with a empty zspage inside system.
> Root cause is zs_page_isolate remove it from  ZS_EMPTY list but not
> call zs_page_putback "schedule_work(&pool->free_work);".  Because
> zs_page_migrate done the job without
> "schedule_work(&pool->free_work);"
> 
> That is why I made the new patch.

Thanks. Now I got it. Could you resend the patch with such detailed
information?

< snip >

> >> +     if (!is_zspage_isolated(zspage)) {
> >> +             /*
> >> +              * The page and class is locked, we cannot free zspage
> >> +              * immediately so let's defer.

Please put more words about that why we should calls schedule_work
in here.

Thanks!

> >> +              */
> >> +             if (putback_zspage(class, zspage) == ZS_EMPTY)
> >> +                     schedule_work(&pool->free_work);
> >> +     }
> >>
> >>       reset_page(page);
> >>       put_page(page);
> >> --
> >> 1.9.1
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to majordomo@kvack.org.  For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

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