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Message-Id: <20250211111326.14295-8-dev.jain@arm.com>
Date: Tue, 11 Feb 2025 16:43:16 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org,
david@...hat.com,
willy@...radead.org,
kirill.shutemov@...ux.intel.com
Cc: npache@...hat.com,
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Dev Jain <dev.jain@....com>
Subject: [PATCH v2 07/17] khugepaged: Scan PTEs order-wise
Scan the PTEs order-wise, using the mask of suitable orders for this VMA
derived in conjunction with sysfs THP settings. Scale down the tunables (to
be changed in subsequent patches); in case of collapse failure, we drop down
to the next order. Otherwise, we try to jump to the highest possible order
and then start a fresh scan. Note that madvise(MADV_COLLAPSE) has not been generalized.
Signed-off-by: Dev Jain <dev.jain@....com>
---
mm/khugepaged.c | 97 ++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 83 insertions(+), 14 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 498cb5ad9ff1..fbfd8a78ef51 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -21,6 +21,7 @@
#include <linux/shmem_fs.h>
#include <linux/dax.h>
#include <linux/ksm.h>
+#include <linux/count_zeros.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
@@ -1295,36 +1296,57 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
{
pmd_t *pmd;
pte_t *pte, *_pte;
- int result = SCAN_FAIL, referenced = 0;
- int none_or_zero = 0, shared = 0;
- struct page *page = NULL;
struct folio *folio = NULL;
- unsigned long _address;
+ int result = SCAN_FAIL;
spinlock_t *ptl;
- int node = NUMA_NO_NODE, unmapped = 0;
+ unsigned int max_ptes_shared, max_ptes_none, max_ptes_swap;
+ int referenced, shared, none_or_zero, unmapped;
+ unsigned long _address, orig_address = address;
+ int node = NUMA_NO_NODE;
bool writable = false;
+ unsigned long orders, orig_orders;
+ int order, prev_order;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+ orders = thp_vma_allowable_orders(vma, vma->vm_flags,
+ TVA_IN_PF | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL_ANON);
+ orders = thp_vma_suitable_orders(vma, address, orders);
+ orig_orders = orders;
+ order = highest_order(orders);
+
+ /* MADV_COLLAPSE needs to work irrespective of sysfs setting */
+ if (!cc->is_khugepaged)
+ order = HPAGE_PMD_ORDER;
+
+scan_pte_range:
+
+ max_ptes_shared = khugepaged_max_ptes_shared >> (HPAGE_PMD_ORDER - order);
+ max_ptes_none = khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - order);
+ max_ptes_swap = khugepaged_max_ptes_swap >> (HPAGE_PMD_ORDER - order);
+ referenced = 0, shared = 0, none_or_zero = 0, unmapped = 0;
+
+ /* Check pmd after taking mmap lock */
result = find_pmd_or_thp_or_none(mm, address, &pmd);
if (result != SCAN_SUCCEED)
goto out;
memset(cc->node_load, 0, sizeof(cc->node_load));
nodes_clear(cc->alloc_nmask);
+
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!pte) {
result = SCAN_PMD_NULL;
goto out;
}
- for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR;
+ for (_address = address, _pte = pte; _pte < pte + (1UL << order);
_pte++, _address += PAGE_SIZE) {
pte_t pteval = ptep_get(_pte);
if (is_swap_pte(pteval)) {
++unmapped;
if (!cc->is_khugepaged ||
- unmapped <= khugepaged_max_ptes_swap) {
+ unmapped <= max_ptes_swap) {
/*
* Always be strict with uffd-wp
* enabled swap entries. Please see
@@ -1345,7 +1367,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
++none_or_zero;
if (!userfaultfd_armed(vma) &&
(!cc->is_khugepaged ||
- none_or_zero <= khugepaged_max_ptes_none)) {
+ none_or_zero <= max_ptes_none)) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
@@ -1369,12 +1391,11 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
if (pte_write(pteval))
writable = true;
- page = vm_normal_page(vma, _address, pteval);
- if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
+ folio = vm_normal_folio(vma, _address, pteval);
+ if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
result = SCAN_PAGE_NULL;
goto out_unmap;
}
- folio = page_folio(page);
if (!folio_test_anon(folio)) {
result = SCAN_PAGE_ANON;
@@ -1390,7 +1411,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
if (folio_likely_mapped_shared(folio)) {
++shared;
if (cc->is_khugepaged &&
- shared > khugepaged_max_ptes_shared) {
+ shared > max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
goto out_unmap;
@@ -1447,7 +1468,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
result = SCAN_PAGE_RO;
} else if (cc->is_khugepaged &&
(!referenced ||
- (unmapped && referenced < HPAGE_PMD_NR / 2))) {
+ (unmapped && referenced < (1UL << order) / 2))) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
@@ -1456,10 +1477,58 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
pte_unmap_unlock(pte, ptl);
if (result == SCAN_SUCCEED) {
result = collapse_huge_page(mm, address, referenced,
- unmapped, HPAGE_PMD_ORDER, cc);
+ unmapped, order, cc);
/* collapse_huge_page will return with the mmap_lock released */
*mmap_locked = false;
+ /* Skip over this range and decide order */
+ if (result == SCAN_SUCCEED)
+ goto decide_order;
+ }
+ if (result != SCAN_SUCCEED) {
+
+ /* Go to the next order */
+ prev_order = order;
+ order = next_order(&orders, order);
+ if (order < 2) {
+ /* Skip over this range, and decide order */
+ _address = address + (PAGE_SIZE << prev_order);
+ _pte = pte + (1UL << prev_order);
+ goto decide_order;
+ }
+ goto maybe_mmap_lock;
}
+
+decide_order:
+ /* Immediately exit on exhaustion of range */
+ if (_address == orig_address + (PAGE_SIZE << HPAGE_PMD_ORDER))
+ goto out;
+
+ /* Get highest order possible starting from address */
+ order = count_trailing_zeros(_address >> PAGE_SHIFT);
+
+ orders = orig_orders & ((1UL << (order + 1)) - 1);
+ if (!(orders & (1UL << order)))
+ order = next_order(&orders, order);
+
+ /* This should never happen, since we are on an aligned address */
+ BUG_ON(cc->is_khugepaged && order < 2);
+
+ address = _address;
+ pte = _pte;
+
+maybe_mmap_lock:
+ if (!(*mmap_locked)) {
+ mmap_read_lock(mm);
+ *mmap_locked = true;
+ /* Validate VMA after retaking mmap_lock */
+ result = hugepage_vma_revalidate(mm, address, true, &vma,
+ order, cc);
+ if (result != SCAN_SUCCEED) {
+ mmap_read_unlock(mm);
+ goto out;
+ }
+ }
+ goto scan_pte_range;
out:
trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenced,
none_or_zero, result, unmapped);
--
2.30.2
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