Replace arguments avoid_reserve and chg in dequeue_hugetlb_folio_vma() so dequeue_hugetlb_folio_vma() is more understandable.
The new argument, use_hstate_resv, indicates whether the folio to be dequeued should be taken from reservations in hstate.
If use_hstate_resv is true, the folio to be dequeued should be taken from reservations in hstate and hence h->resv_huge_pages is decremented, and the folio is marked so that the reservation is restored.
If use_hstate_resv is false, then a folio needs to be taken from the pool and hence there must exist available_huge_pages(h), failing which, goto err.
The bool use_hstate_resv can be reused within dequeue_hugetlb_folio_vma()'s caller, alloc_hugetlb_folio().
No functional changes are intended.
As proof, the original two if conditions
!vma_has_reserves(vma, chg) && !available_huge_pages(h)
and
avoid_reserve && !available_huge_pages(h)
can be combined into
(avoid_reserve || !vma_has_reserves(vma, chg)) && !available_huge_pages(h).
Applying de Morgan's theorem on
avoid_reserve || !vma_has_reserves(vma, chg)
yields
!avoid_reserve && vma_has_reserves(vma, chg),
hence the simplification is correct.
Signed-off-by: Ackerley Tng ackerleytng@google.com --- mm/hugetlb.c | 33 +++++++++++---------------------- 1 file changed, 11 insertions(+), 22 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index aaf508be0a2b..af5c6bbc9ff0 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1280,8 +1280,9 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg) }
/* - * Only the process that called mmap() has reserves for - * private mappings. + * Only the process that called mmap() has reserves for private + * mappings. A child process with MAP_PRIVATE mappings created by their + * parent have no page reserves. */ if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) { /* @@ -1393,8 +1394,7 @@ static unsigned long available_huge_pages(struct hstate *h)
static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h, struct vm_area_struct *vma, - unsigned long address, int avoid_reserve, - long chg) + unsigned long address, bool use_hstate_resv) { struct folio *folio = NULL; struct mempolicy *mpol; @@ -1402,16 +1402,7 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h, nodemask_t *nodemask; int nid;
- /* - * A child process with MAP_PRIVATE mappings created by their parent - * have no page reserves. This check ensures that reservations are - * not "stolen". The child may still get SIGKILLed - */ - if (!vma_has_reserves(vma, chg) && !available_huge_pages(h)) - goto err; - - /* If reserves cannot be used, ensure enough pages are in the pool */ - if (avoid_reserve && !available_huge_pages(h)) + if (!use_hstate_resv && !available_huge_pages(h)) goto err;
gfp_mask = htlb_alloc_mask(h); @@ -1429,7 +1420,7 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h, folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask, nid, nodemask);
- if (folio && !avoid_reserve && vma_has_reserves(vma, chg)) { + if (folio && use_hstate_resv) { folio_set_hugetlb_restore_reserve(folio); h->resv_huge_pages--; } @@ -3130,6 +3121,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, struct mem_cgroup *memcg; bool deferred_reserve; gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL; + bool use_hstate_resv;
memcg = get_mem_cgroup_from_current(); memcg_charge_ret = mem_cgroup_hugetlb_try_charge(memcg, gfp, nr_pages); @@ -3190,20 +3182,17 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, if (ret) goto out_uncharge_cgroup_reservation;
+ use_hstate_resv = !avoid_reserve && vma_has_reserves(vma, gbl_chg); + spin_lock_irq(&hugetlb_lock); - /* - * glb_chg is passed to indicate whether or not a page must be taken - * from the global free pool (global change). gbl_chg == 0 indicates - * a reservation exists for the allocation. - */ - folio = dequeue_hugetlb_folio_vma(h, vma, addr, avoid_reserve, gbl_chg); + folio = dequeue_hugetlb_folio_vma(h, vma, addr, use_hstate_resv); if (!folio) { spin_unlock_irq(&hugetlb_lock); folio = alloc_buddy_hugetlb_folio_with_mpol(h, vma, addr); if (!folio) goto out_uncharge_cgroup; spin_lock_irq(&hugetlb_lock); - if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) { + if (use_hstate_resv) { folio_set_hugetlb_restore_reserve(folio); h->resv_huge_pages--; }