Re: [RFC PATCH 3/8] hugetlb: create remove_hugetlb_page() to separate functionality

[Mike Kravetz]

On 3/22/21 7:15 AM, Michal Hocko wrote:
> On Fri 19-03-21 15:42:04, Mike Kravetz wrote:
>> The new remove_hugetlb_page() routine is designed to remove a hugetlb
>> page from hugetlbfs processing.  It will remove the page from the active
>> or free list, update global counters and set the compound page
>> destructor to NULL so that PageHuge() will return false for the 'page'.
>> After this call, the 'page' can be treated as a normal compound page or
>> a collection of base size pages.
>>
>> remove_hugetlb_page is to be called with the hugetlb_lock held.
>>
>> Creating this routine and separating functionality is in preparation for
>> restructuring code to reduce lock hold times.
> 
> I like this! Counters handling both in __free_huge_page and
> update_and_free_page is really confusing.
> 
> 
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> ---
>>  mm/hugetlb.c | 70 ++++++++++++++++++++++++++++++++++------------------
>>  1 file changed, 46 insertions(+), 24 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index c537274c2a38..ae185d3315e0 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1306,6 +1306,46 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>>  						unsigned int order) { }
>>  #endif
>>  
>> +/*
>> + * Remove hugetlb page from lists, and update dtor so that page appears
>> + * as just a compound page.  A reference is held on the page.
>> + * NOTE: hugetlb specific page flags stored in page->private are not
>> + *	 automatically cleared.  These flags may be used in routines
>> + *	 which operate on the resulting compound page.
>> + *
>> + * Must be called with hugetlb lock held.
>> + */
>> +static void remove_hugetlb_page(struct hstate *h, struct page *page,
>> +							bool adjust_surplus)
>> +{
>> +	int nid = page_to_nid(page);
>> +
> 
> I think we want lockdep_assert_held here. Lockdep asserts are not used
> in this code but now that you are touching it then it is probably better
> to start adding them. What do you think?
> 

Yes, with this type of change we add lockdep tests/qualifiers.  They are
lacking in the code, and would be helpful.

I will add them.
-- 
Mike Kravetz