Minchan Kim <minchan@xxxxxxxxxx> writes:
> Hi,
>
> On Thu, Jun 16, 2016 at 08:03:54PM -0700, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@xxxxxxxxx>
>>
>> madvise_free_huge_pmd should return 0 if the fallback PTE operations are
>> required. In madvise_free_huge_pmd, if part pages of THP are discarded,
>> the THP will be split and fallback PTE operations should be used if
>> splitting succeeds. But the original code will make fallback PTE
>> operations skipped, after splitting succeeds. Fix that via make
>> madvise_free_huge_pmd return 0 after splitting successfully, so that the
>> fallback PTE operations will be done.
>
> You're right. Thanks!
>
>>
>> Know issues: if my understanding were correct, return 1 from
>> madvise_free_huge_pmd means the following processing for the PMD should
>> be skipped, while return 0 means the following processing is still
>> needed. So the function should return 0 only if the THP is split
>> successfully or the PMD is not trans huge. But the pmd_trans_unstable
>> after madvise_free_huge_pmd guarantee the following processing will be
>> skipped for huge PMD. So current code can run properly. But if my
>> understanding were correct, we can clean up return code of
>> madvise_free_huge_pmd accordingly.
>
> I like your clean up. Just a minor comment below.
>
>>
>> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> ---
>> mm/huge_memory.c | 7 +------
>> 1 file changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 2ad52d5..64dc95d 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>
> First of all, let's change ret from int to bool.
> And then, add description in the function entry.
Yes. bool looks better than int.
> /*
> * Return true if we do MADV_FREE successfully on entire pmd page.
> * Otherwise, return false.
> */
This way, we need to return false if we failed to split huge page, this
will cause unnecessary pmd_trans_unstable check. How about to change
the comments to
/*
* Return true if we finished processing entire pmd page and needn't
* fall back pte processing. Otherwise, return false.
*/
Best Regards,
Huang, Ying
> And do not set to 1 if it is huge_zero_pmd but just goto out to
> return false.
>
> Thanks!
>
>> @@ -1655,14 +1655,9 @@ int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>> if (next - addr != HPAGE_PMD_SIZE) {
>> get_page(page);
>> spin_unlock(ptl);
>> - if (split_huge_page(page)) {
>> - put_page(page);
>> - unlock_page(page);
>> - goto out_unlocked;
>> - }
>> + split_huge_page(page);
>> put_page(page);
>> unlock_page(page);
>> - ret = 1;
>> goto out_unlocked;
>> }
>>
>> --
>> 2.8.1
>>
>> --
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