On Sun, Nov 08, 2020 at 10:11:01PM +0800, Muchun Song wrote:
> +static inline int freed_vmemmap_hpage(struct page *page)
> +{
> + return atomic_read(&page->_mapcount) + 1;
> +}
> +
> +static inline int freed_vmemmap_hpage_inc(struct page *page)
> +{
> + return atomic_inc_return_relaxed(&page->_mapcount) + 1;
> +}
> +
> +static inline int freed_vmemmap_hpage_dec(struct page *page)
> +{
> + return atomic_dec_return_relaxed(&page->_mapcount) + 1;
> +}
Are these relaxed any different that the normal ones on x86_64?
I got confused following the macros.
> +static void __free_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
> + unsigned long start,
> + unsigned int nr_free,
> + struct list_head *free_pages)
> +{
> + /* Make the tail pages are mapped read-only. */
> + pgprot_t pgprot = PAGE_KERNEL_RO;
> + pte_t entry = mk_pte(reuse, pgprot);
> + unsigned long addr;
> + unsigned long end = start + (nr_free << PAGE_SHIFT);
See below.
> +static void __free_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
> + unsigned long addr,
> + struct list_head *free_pages)
> +{
> + unsigned long next;
> + unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE;
> + unsigned long end = addr + vmemmap_pages_size_per_hpage(h);
> + struct page *reuse = NULL;
> +
> + addr = start;
> + do {
> + unsigned int nr_pages;
> + pte_t *ptep;
> +
> + ptep = pte_offset_kernel(pmd, addr);
> + if (!reuse)
> + reuse = pte_page(ptep[-1]);
Can we define a proper name for that instead of -1?
e.g: TAIL_PAGE_REUSE or something like that.
> +
> + next = vmemmap_hpage_addr_end(addr, end);
> + nr_pages = (next - addr) >> PAGE_SHIFT;
> + __free_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages,
> + free_pages);
Why not passing next instead of nr_pages? I think it makes more sense.
As a bonus we can kill the variable.
> +static void split_vmemmap_huge_page(struct hstate *h, struct page *head,
> + pmd_t *pmd)
> +{
> + pgtable_t pgtable;
> + unsigned long start = (unsigned long)head & VMEMMAP_HPAGE_MASK;
> + unsigned long addr = start;
> + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> + while (nr-- && (pgtable = vmemmap_pgtable_withdraw(head))) {
The same with previous patches, I would scrap "nr" and its use.
> + VM_BUG_ON(freed_vmemmap_hpage(pgtable));
I guess here we want to check whether we already call free_huge_page_vmemmap
on this range?
For this to have happened, the locking should have failed, right?
> +static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> + pmd_t *pmd;
> + spinlock_t *ptl;
> + LIST_HEAD(free_pages);
> +
> + if (!free_vmemmap_pages_per_hpage(h))
> + return;
> +
> + pmd = vmemmap_to_pmd(head);
> + ptl = vmemmap_pmd_lock(pmd);
> + if (vmemmap_pmd_huge(pmd)) {
> + VM_BUG_ON(!pgtable_pages_to_prealloc_per_hpage(h));
I think that checking for free_vmemmap_pages_per_hpage is enough.
In the end, pgtable_pages_to_prealloc_per_hpage uses
free_vmemmap_pages_per_hpage.
--
Oscar Salvador
SUSE L3
