On Thu, Jan 14, 2021 at 7:52 PM Oscar Salvador [off-list ref] wrote:

On Thu, Jan 14, 2021 at 06:54:30PM +0800, Muchun Song wrote:

quoted

I think this approach may be only suitable for generic huge page only.
So we can implement it only for huge page.

Hi Oscar,

What's your opinion about this?

I tried something like:

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_page) {
                BUG_ON(pte_none(*pte));

                walk->reuse_page = pte_page(*pte++);
                addr = walk->remap_start;
        }

        for (; addr != end; addr += PAGE_SIZE, pte++) {
                BUG_ON(pte_none(*pte));

                walk->remap_pte(pte, addr, walk);
        }
}

void vmemmap_remap_free(unsigned long start, unsigned long end,
                        unsigned long reuse)
{
        LIST_HEAD(vmemmap_pages);
        struct vmemmap_remap_walk walk = {
                .remap_pte      = vmemmap_remap_pte,
                .reuse_addr     = reuse,
                .remap_start = start,
                .vmemmap_pages  = &vmemmap_pages,
        };

        BUG_ON(start != reuse + PAGE_SIZE);

        vmemmap_remap_range(reuse, end, &walk);
        free_vmemmap_page_list(&vmemmap_pages);
}

but it might overcomplicate things and I am not sure it is any better.
So I am fine with keeping it as is.
Should another user come in the future, we can always revisit.
Maybe just add a little comment in vmemmap_pte_range(), explaining while we
are "+= PAGE_SIZE" for address and I would like to see a comment in
vmemmap_remap_free why the BUG_ON and more important what it is checking.

OK, I will add some comments to explain why we do this in
vmemmap_remap_free and vmemmap_remap_free. Thanks.

--
Oscar Salvador
SUSE L3