Re: [PATCH 08/10] mm/hugetlb: return non-isolated page in the loop instead of break and check

Wei Yang
2020-08-07T14:32:48Z

On Fri, Aug 07, 2020 at 09:09:31PM +0800, Baoquan He wrote:
>On 08/07/20 at 05:12pm, Wei Yang wrote:
>> Function dequeue_huge_page_node_exact() iterates the free list and
>> return the first non-isolated one.
>>
>> Instead of break and check the loop variant, we could return in the loop
>> directly. This could reduce some redundant check.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>> ---
>> mm/hugetlb.c | 26 ++++++++++++--------------
>> 1 file changed, 12 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index b8e844911b5a..9473eb6800e9 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1035,20 +1035,18 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
>> {
>> struct page *page;
>>
>> - list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
>> - if (!PageHWPoison(page))
>> - break;
>
>I don't see how it can reduce redundant check, just two different
>styles.
>

list_for_each_entry() stops by checking whether the item reach list head.

>> - /*
>> - * if 'non-isolated free hugepage' not found on the list,
>> - * the allocation fails.
>
>But the above code comment seems stale, it checks HWPoision page()
>directly, but not the old isolated page checking.
>
>> - */
>> - if (&h->hugepage_freelists[nid] == &page->lru)
>> - return NULL;

And here the check is done again, if we really iterate the whole list.

By take the code in the loop, we can avoid this check.

>> - list_move(&page->lru, &h->hugepage_activelist);
>> - set_page_refcounted(page);
>> - h->free_huge_pages--;
>> - h->free_huge_pages_node[nid]--;
>> - return page;
>> + list_for_each_entry(page, &h->hugepage_freelists[nid], lru) {
>> + if (PageHWPoison(page))
>> + continue;
>> +
>> + list_move(&page->lru, &h->hugepage_activelist);
>> + set_page_refcounted(page);
>> + h->free_huge_pages--;
>> + h->free_huge_pages_node[nid]--;
>> + return page;
>> + }
>> +
>> + return NULL;
>> }
>>
>> static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask, int nid,
>> --
>> 2.20.1 (Apple Git-117)
>>
>>

--
Wei Yang
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