Messages in this thread | | | Date | Mon, 5 Feb 2024 20:38:53 +0800 | Subject | Re: [PATCH] mm: hugetlb: fix hugetlb allocation failure when handling freed or in-use hugetlb | From | Baolin Wang <> |
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On 2/5/2024 5:31 PM, Michal Hocko wrote: > 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@linux.alibaba.com> >> --- >> 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
Nope, just did a simple patch to ignore the allocation failure.
> could have easily dropped the lock, allocate a page and then goto retry. > This would actually save an allocation.
Yes, will do. Thanks.
> 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; > }
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