On Mon 05-02-24 11:54:17, Baolin Wang wrote:
> When handling the freed hugetlb or in-use hugetlb, we should ignore the
> failure of alloc_buddy_hugetlb_folio() to dissolve the old hugetlb successfully,
> since we did not use the new allocated hugetlb in this 2 cases.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> mm/hugetlb.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9d996fe4ecd9..212ab331d355 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3042,9 +3042,8 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
> * 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);
> + if (new_folio)
> + __prep_new_hugetlb_folio(h, new_folio);
Is there any reason why you haven't moved the allocation to the only
branch that actually needs it? I know that we hold hugetlb lock but you
could have easily dropped the lock, allocate a page and then goto retry.
This would actually save an allocation.
Something like this:
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ed1581b670d4..db5f72b94422 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -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 +3061,15 @@ 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 +3097,11 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
free_new:
spin_unlock_irq(&hugetlb_lock);
- /* 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);
+ 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;
}
--
Michal Hocko
SUSE Labs
