On Thu, Dec 17, 2020 at 08:12:55PM +0800, Muchun Song wrote:
> +static inline void free_bootmem_page(struct page *page)
> +{
> + unsigned long magic = (unsigned long)page->freelist;
> +
> + /*
> + * The reserve_bootmem_region sets the reserved flag on bootmem
> + * pages.
> + */
> + VM_WARN_ON(page_ref_count(page) != 2);
> +
> + if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
> + put_page_bootmem(page);
> + else
> + VM_WARN_ON(1);
Ideally, I think we want to see what how the page looks since its state
is not what we expected, so maybe join both conditions and use dump_page().
> + * By removing redundant page structs for HugeTLB pages, memory can returned to
^^ be
> + * the buddy allocator for other uses.
[...]
> +void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> + unsigned long vmemmap_addr = (unsigned long)head;
> +
> + if (!free_vmemmap_pages_per_hpage(h))
> + return;
> +
> + vmemmap_remap_free(vmemmap_addr + RESERVE_VMEMMAP_SIZE,
> + free_vmemmap_pages_size_per_hpage(h));
I am not sure what others think, but I would like to see vmemmap_remap_free taking
three arguments: start, end, and reuse addr, e.g:
void free_huge_page_vmemmap(struct hstate *h, struct page *head)
{
unsigned long vmemmap_addr = (unsigned long)head;
unsigned long vmemmap_end, vmemmap_reuse;
if (!free_vmemmap_pages_per_hpage(h))
return;
vmemmap_addr += RESERVE_MEMMAP_SIZE;
vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
}
The reason for me to do this is to let the callers of vmemmap_remap_free decide
__what__ they want to remap.
More on this below.
> +static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
> + unsigned long end,
> + struct vmemmap_remap_walk *walk)
> +{
> + pte_t *pte;
> +
> + pte = pte_offset_kernel(pmd, addr);
> +
> + if (walk->reuse_addr == addr) {
> + BUG_ON(pte_none(*pte));
> + walk->reuse_page = pte_page(*pte++);
> + addr += PAGE_SIZE;
> + }
Although it is quite obvious, a brief comment here pointing out what are we
doing and that this is meant to be set only once would be nice.
> +static void vmemmap_remap_range(unsigned long start, unsigned long end,
> + struct vmemmap_remap_walk *walk)
> +{
> + unsigned long addr = start - PAGE_SIZE;
> + unsigned long next;
> + pgd_t *pgd;
> +
> + VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
> + VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
> +
> + walk->reuse_page = NULL;
> + walk->reuse_addr = addr;
With the change I suggested above, struct vmemmap_remap_walk should be
initialitzed at once in vmemmap_remap_free, so this should not longer be needed.
(And btw, you do not need to set reuse_page to NULL, the way you init the struct
in vmemmap_remap_free makes sure to null any field you do not explicitly set).
> +static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
> + struct vmemmap_remap_walk *walk)
> +{
> + /*
> + * Make the tail pages are mapped with read-only to catch
> + * illegal write operation to the tail pages.
"Remap the tail pages as read-only to ..."
> + */
> + pgprot_t pgprot = PAGE_KERNEL_RO;
> + pte_t entry = mk_pte(walk->reuse_page, pgprot);
> + struct page *page;
> +
> + page = pte_page(*pte);
struct page *page = pte_page(*pte);
since you did the same for the other two.
> + list_add(&page->lru, walk->vmemmap_pages);
> +
> + set_pte_at(&init_mm, addr, pte, entry);
> +}
> +
> +/**
> + * vmemmap_remap_free - remap the vmemmap virtual address range
> + * [start, start + size) to the page which
> + * [start - PAGE_SIZE, start) is mapped,
> + * then free vmemmap pages.
> + * @start: start address of the vmemmap virtual address range
> + * @size: size of the vmemmap virtual address range
> + */
> +void vmemmap_remap_free(unsigned long start, unsigned long size)
> +{
> + unsigned long end = start + size;
> + LIST_HEAD(vmemmap_pages);
> +
> + struct vmemmap_remap_walk walk = {
> + .remap_pte = vmemmap_remap_pte,
> + .vmemmap_pages = &vmemmap_pages,
> + };
As stated above, this would become:
void vmemmap_remap_free(unsigned long start, unsigned long end,
usigned long reuse)
{
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.reuse_addr = reuse,
.remap_pte = vmemmap_remap_pte,
.vmemmap_pages = &vmemmap_pages,
};
You might have had your reasons to do this way, but this looks more natural
to me, with the plus that callers of vmemmap_remap_free can specify
what they want to remap.
--
Oscar Salvador
SUSE L3
