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. Moreover,
moving the allocation into the free hugetlb handling branch.
Signed-off-by: Baolin Wang <[email protected]>
---
Changes from v1:
- Update the suject line per Muchun.
- Move the allocation into the free hugetlb handling branch per Michal.
---
mm/hugetlb.c | 40 ++++++++++++++++++++++++----------------
1 file changed, 24 insertions(+), 16 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9d996fe4ecd9..4899167d3652 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3031,21 +3031,9 @@ 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)) {
@@ -3075,6 +3063,24 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
cond_resched();
goto retry;
} else {
+ if (!new_folio) {
+ spin_unlock_irq(&hugetlb_lock);
+ /*
+ * Before dissolving the free hugetlb, 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);
+ goto retry;
+ }
+
/*
* Ok, old_folio is still a genuine free hugepage. Remove it from
* the freelist and decrease the counters. These will be
@@ -3102,9 +3108,11 @@ 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;
}
--
2.39.3
On Mon 05-02-24 20:50:51, 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. Moreover,
> moving the allocation into the free hugetlb handling branch.
The changelog is a bit hard for me to understand. What about the
following instead?
alloc_and_dissolve_hugetlb_folio preallocates a new huge 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.
[...]
> @@ -3075,6 +3063,24 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
> cond_resched();
> goto retry;
> } else {
> + if (!new_folio) {
> + spin_unlock_irq(&hugetlb_lock);
> + /*
> + * Before dissolving the free hugetlb, 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.
> + */
This comment is not really needed anymore IMHO.
> + 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
--
Michal Hocko
SUSE Labs
On 2/5/2024 10:47 PM, Michal Hocko wrote:
> On Mon 05-02-24 20:50:51, 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. Moreover,
>> moving the allocation into the free hugetlb handling branch.
>
> The changelog is a bit hard for me to understand. What about the
> following instead?
> alloc_and_dissolve_hugetlb_folio preallocates a new huge 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.
Looks better. Thanks.
>> @@ -3075,6 +3063,24 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
>> cond_resched();
>> goto retry;
>> } else {
>> + if (!new_folio) {
>> + spin_unlock_irq(&hugetlb_lock);
>> + /*
>> + * Before dissolving the free hugetlb, 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.
>> + */
>
> This comment is not really needed anymore IMHO.
Acked.
>
>> + 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
>