On 6/21/23 11:42 AM, Andrei Vagin wrote:
On Mon, Jun 19, 2023 at 11:06:36AM +0500, Muhammad Usama Anjum wrote:
On 6/17/23 11:39 AM, Andrei Vagin wrote:
On Thu, Jun 15, 2023 at 07:11:41PM +0500, Muhammad Usama Anjum wrote:
+static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
unsigned long end, struct mm_walk *walk)+{
- bool is_written, flush = false, is_interesting = true;
- struct pagemap_scan_private *p = walk->private;
- struct vm_area_struct *vma = walk->vma;
- unsigned long bitmap, addr = end;
- pte_t *pte, *orig_pte, ptent;
- spinlock_t *ptl;
- int ret = 0;
- arch_enter_lazy_mmu_mode();
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- ptl = pmd_trans_huge_lock(pmd, vma);
- if (ptl) {
unsigned long n_pages = (end - start)/PAGE_SIZE;if (p->max_pages && n_pages > p->max_pages - p->found_pages)n_pages = p->max_pages - p->found_pages;is_written = !is_pmd_uffd_wp(*pmd);/** Break huge page into small pages if the WP operation need to* be performed is on a portion of the huge page.*/if (is_written && IS_PM_SCAN_WP(p->flags) &&n_pages < HPAGE_SIZE/PAGE_SIZE) {spin_unlock(ptl);split_huge_pmd(vma, pmd, start);goto process_smaller_pages;}bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file,pmd_present(*pmd), is_swap_pmd(*pmd));if (IS_PM_SCAN_GET(p->flags)) {is_interesting = pagemap_scan_is_interesting_page(bitmap, p);if (is_interesting)ret = pagemap_scan_output(bitmap, p, start, n_pages);}if (IS_PM_SCAN_WP(p->flags) && is_written && is_interesting &&ret >= 0) {make_uffd_wp_pmd(vma, start, pmd);flush_tlb_range(vma, start, end);}spin_unlock(ptl);arch_leave_lazy_mmu_mode();return ret;- }
+process_smaller_pages: +#endif
- orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
- if (!pte) {
Do we need to unlock ptl here?
spin_unlock(ptl);No, please look at these recently merged patches: https://lore.kernel.org/all/c1c9a74a-bc5b-15ea-e5d2-8ec34bc921d@google.com
walk->action = ACTION_AGAIN;return 0;- }
- for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
ptent = ptep_get(pte);is_written = !is_pte_uffd_wp(ptent);bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file,pte_present(ptent), is_swap_pte(ptent));The vma->vm_file check isn't correct in this case. You can look when pte_to_pagemap_entry sets PM_FILE. This flag is used to detect what pages have a file backing store and what pages are anonymous.
I'll update.
I was trying to integrate this new interace into CRIU and I found one more thing that is required. We need to detect zero pages.
Should we name it ZERO_PFN_PRESENT_PAGE to be exact or what?
IMHO, ZERO_PFN_PRESENT_PAGE looks a bit monstrous. It looks like zero page is a proper noun in the kernel, so PAGE_IS_ZERO might be a good choice here, but it is up to you.
It should look something like this:
#define PM_SCAN_FLAGS(wt, file, present, swap, zero) \ ((wt) | ((file) << 1) | ((present) << 2) | ((swap) << 3) | ((zero) << 4))
bitmap = PM_SCAN_FLAGS(is_written, page && !PageAnon(page), pte_present(ptent), is_swap_pte(ptent), pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
Okay. Can you please confirm my assumptions:
- A THP cannot be file backed. (PM_FILE isn't being set for THP case)
Currently THP only works for anonymous memory mappings and tmpfs/shmem. But in the future it can expand to other filesystems.https://www.kernel.org/doc/html/next/admin-guide/mm/transhuge.html
so THP can be "file backed".
- A hole is also not file backed.
A hole isn't present in memory. So its pfn would be zero. But as it isn't present, it shouldn't report zero page. Right? For hole::
PM_SCAN_FLAGS(false, false, false, false, false)
This looks correct to me.
Thanks. I'll sent next version in a few minutes.