Re: [PATCH v4 4/8] hugetlb: create remove_hugetlb_page() to separate functionality

[Michal Hocko <mhocko@suse.com>]

On Mon 05-04-21 16:00:39, 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.
> 
> update_and_free_page no longer decrements h->nr_huge_pages{_node} as
> this is performed in remove_hugetlb_page.  The only functionality
> performed by update_and_free_page is to free the base pages to the lower
> level allocators.
> 
> update_and_free_page is typically called after remove_hugetlb_page.
> 
> 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.  This commit should not
> introduce any changes to functionality.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Btw. I would prefer to reverse the ordering of this and Oscar's
patchset. This one is a bug fix which might be interesting for stable
backports while Oscar's work can be looked as a general functionality
improvement.

> @@ -2298,6 +2312,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>  		/*
>  		 * Freed from under us. Drop new_page too.
>  		 */
> +		remove_hugetlb_page(h, new_page, false);
>  		update_and_free_page(h, new_page);
>  		goto unlock;
>  	} else if (page_count(old_page)) {
> @@ -2305,6 +2320,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
>  		 * Someone has grabbed the page, try to isolate it here.
>  		 * Fail with -EBUSY if not possible.
>  		 */
> +		remove_hugetlb_page(h, new_page, false);
>  		update_and_free_page(h, new_page);
>  		spin_unlock(&hugetlb_lock);
>  		if (!isolate_huge_page(old_page, list))

the page is not enqued anywhere here so remove_hugetlb_page would blow
when linked list debugging is enabled.
-- 
Michal Hocko
SUSE Labs