Commit 831bc31a authored by Baolin Wang's avatar Baolin Wang Committed by Andrew Morton
Browse files

mm: hugetlb: improve the handling of hugetlb allocation failure for freed or in-use hugetlb 

alloc_and_dissolve_hugetlb_folio() preallocates a new hugetlb page before
it takes hugetlb_lock.  In 3 out of 4 cases the page is not really used
and therefore the newly allocated page is just freed right away.  This is
wasteful and it might cause pre-mature failures in those cases.

Address that by moving the allocation down to the only case (hugetlb page
is really in the free pages pool).  We need to drop hugetlb_lock to do so
and therefore need to recheck the page state after regaining it.

The patch is more of a cleanup than an actual fix to an existing problem. 
There are no known reports about pre-mature failures.

Link: https://lkml.kernel.org/r/62890fd60b1ecd5bf1cdc476c973f60fe37aa0cb.1707181934.git.baolin.wang@linux.alibaba.com


Signed-off-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Reviewed-by: default avatarMuchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 055267fe

mm/hugetlb.c

+16 −16
Original line number Diff line number Diff line
@@ -3029,21 +3029,9 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, 
{

	gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;

	int nid = folio_nid(old_folio);

	struct folio *new_folio;

	struct folio *new_folio = NULL;

	int ret = 0;



	/*

	 * Before dissolving the folio, we need to allocate a new one for the

	 * pool to remain stable.  Here, we allocate the folio and 'prep' it

	 * by doing everything but actually updating counters and adding to

	 * the pool.  This simplifies and let us do most of the processing

	 * under the lock.

	 */

	new_folio = alloc_buddy_hugetlb_folio(h, gfp_mask, nid, NULL, NULL);

	if (!new_folio)

		return -ENOMEM;

	__prep_new_hugetlb_folio(h, new_folio);



retry:

	spin_lock_irq(&hugetlb_lock);

	if (!folio_test_hugetlb(old_folio)) {
@@ -3073,6 +3061,16 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, 
		cond_resched();

		goto retry;

	} else {

		if (!new_folio) {

			spin_unlock_irq(&hugetlb_lock);

			new_folio = alloc_buddy_hugetlb_folio(h, gfp_mask, nid,

							      NULL, NULL);

			if (!new_folio)

				return -ENOMEM;

			__prep_new_hugetlb_folio(h, new_folio);

			goto retry;

		}



		/*

		 * Ok, old_folio is still a genuine free hugepage. Remove it from

		 * the freelist and decrease the counters. These will be
@@ -3100,9 +3098,11 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, 


free_new:

	spin_unlock_irq(&hugetlb_lock);

	if (new_folio) {

		/* Folio has a zero ref count, but needs a ref to be freed */

		folio_ref_unfreeze(new_folio, 1);

		update_and_free_hugetlb_folio(h, new_folio, false);

	}



	return ret;

}