Re: [PATCH v2] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Hui Zhu]

Hi Minchan,

2017-08-16 10:13 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>:
> Hi Hui,
>
> On Mon, Aug 14, 2017 at 05:56:30PM +0800, Hui Zhu wrote:
>> After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
>
> This patch is not merged yet so the hash is invalid.
> That means we may fold this patch to [1] in current mmotm.
>
> [1] zsmalloc-zs_page_migrate-skip-unnecessary-loops-but-not-return-ebusy-if-zspage-is-not-inuse-fix.patch
>
>> loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
>> can handle the ZS_EMPTY zspage.
>>
>> But I got some false in zs_page_isolate:
>>       if (get_zspage_inuse(zspage) == 0) {
>>               spin_unlock(&class->lock);
>>               return false;
>>       }
>
> I also realized we should make zs_page_isolate succeed on empty zspage
> because we allow the empty zspage migration from now on.
> Could you send a patch for that as well?

OK.  I will make a patch for that later.

Thanks,
Hui

>
>> The page of this zspage was migrated in before.
>>
>> The reason is commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip
>> unnecessary loops but not return -EBUSY if zspage is not inuse") just
>> handle the "page" but not "newpage" then 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);"
>>
>> 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@xxxxxxxxxx>
>> ---
>>  mm/zsmalloc.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index 62457eb..c6cc77c 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -2035,8 +2035,17 @@ 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)) {
>> +             /*
>> +              * Page will be freed in following part. But newpage and
>> +              * zspage will stay in system if zspage is in ZS_EMPTY
>> +              * list.  So call free_work to free it.
>> +              * The page and class is locked, we cannot free zspage
>> +              * immediately so let's defer.
>> +              */
>
> How about this?
>
>                 /*
>                  * Since we allow empty zspage migration, putback of zspage
>                  * should free empty zspage. Otherwise, it could make a leak
>                  * until upcoming free_work is done, which isn't guaranteed.
>                  */
>> +             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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