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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 Acked-by: Peter Xu Reviewed-by: Oscar Salvador --- mm/hugetlb.c | 33 +++++++++++---------------------- 1 file changed, 11 insertions(+), 22 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 190fa05635f4..73165c670739 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1281,8 +1281,9 @@ static bool vma_has_reserves(struct vm_area_struct *v= ma, 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)) { /* @@ -1394,8 +1395,7 @@ static unsigned long available_huge_pages(struct hsta= te *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 =3D NULL; struct mempolicy *mpol; @@ -1403,16 +1403,7 @@ static struct folio *dequeue_hugetlb_folio_vma(struc= t 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 =3D htlb_alloc_mask(h); @@ -1430,7 +1421,7 @@ static struct folio *dequeue_hugetlb_folio_vma(struct= hstate *h, folio =3D 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--; } @@ -2973,6 +2964,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_stru= ct *vma, struct mem_cgroup *memcg; bool deferred_reserve; gfp_t gfp =3D htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL; + bool use_hstate_resv; memcg =3D get_mem_cgroup_from_current(); memcg_charge_ret =3D mem_cgroup_hugetlb_try_charge(memcg, gfp, nr_pages); @@ -3033,20 +3025,17 @@ struct folio *alloc_hugetlb_folio(struct vm_area_st= ruct *vma, if (ret) goto out_uncharge_cgroup_reservation; + use_hstate_resv =3D !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 =3D=3D 0 indicates - * a reservation exists for the allocation. - */ - folio =3D dequeue_hugetlb_folio_vma(h, vma, addr, avoid_reserve, gbl_chg); + folio =3D dequeue_hugetlb_folio_vma(h, vma, addr, use_hstate_resv); if (!folio) { spin_unlock_irq(&hugetlb_lock); folio =3D 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--; } -- 2.47.0.rc1.288.g06298d1525-goog