Messages in this thread | | | From | Muchun Song <> | Date | Tue, 10 Nov 2020 11:49:27 +0800 | Subject | Re: [External] Re: [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers |
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On Tue, Nov 10, 2020 at 1:21 AM Oscar Salvador <osalvador@suse.de> wrote: > > On Sun, Nov 08, 2020 at 10:10:57PM +0800, Muchun Song wrote: > > +static inline unsigned int pgtable_pages_to_prealloc_per_hpage(struct hstate *h) > > +{ > > + unsigned long vmemmap_size = vmemmap_pages_size_per_hpage(h); > > + > > + /* > > + * No need pre-allocate page tabels when there is no vmemmap pages > > + * to free. > s /tabels/tables/
Thanks.
> > > +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page) > > +{ > > + int i; > > + pgtable_t pgtable; > > + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h); > > + > > + if (!nr) > > + return 0; > > + > > + vmemmap_pgtable_init(page); > > + > > + for (i = 0; i < nr; i++) { > > + pte_t *pte_p; > > + > > + pte_p = pte_alloc_one_kernel(&init_mm); > > + if (!pte_p) > > + goto out; > > + vmemmap_pgtable_deposit(page, virt_to_page(pte_p)); > > + } > > + > > + return 0; > > +out: > > + while (i-- && (pgtable = vmemmap_pgtable_withdraw(page))) > > + pte_free_kernel(&init_mm, page_to_virt(pgtable)); > > would not be enough to: > > while (pgtable = vmemmap_pgtable_withdrag(page)) > pte_free_kernel(&init_mm, page_to_virt(pgtable));
The vmemmap_pgtable_withdraw can not return NULL. So we can not drop the "i--".
> > > + return -ENOMEM; > > +} > > + > > +static void vmemmap_pgtable_free(struct hstate *h, struct page *page) > > +{ > > + pgtable_t pgtable; > > + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h); > > + > > + if (!nr) > > + return; > > We can get rid of "nr" and its check and keep only the check below, right?
Great, the check can go away.
> AFAICS, they go together, e.g: if page_huge_pte does not return null, > it means that we preallocated a pagetable, and viceversa. > > > > + > > + pgtable = page_huge_pte(page); > > + if (!pgtable) > > + return; > > + > > + while (nr-- && (pgtable = vmemmap_pgtable_withdraw(page))) > > + pte_free_kernel(&init_mm, page_to_virt(pgtable)); > > Same as above, that "nr" can go?
Here "nr" can not go. Because the vmemmap_pgtable_withdraw can not return NULL.
Thanks.
> > -- > Oscar Salvador > SUSE L3
-- Yours, Muchun
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