Revert "FROMGIT: mm: improve mprotect(R|W) efficiency on pages referenced once"
This reverts commit b44e46bb047d136bc8977497b6fc2a9f08740321.
Reason for revert:
The patch has not yet landed upstream, following feedback from Linus:
https://lore.kernel.org/all/CAHk-=wj4KCujAH_oPh40Bkp48amM4MXr+8AcbZ=qd5LF4Q+TDg@mail.gmail.com/#t
Bug: 213339151
Signed-off-by: Peter Collingbourne <pcc@google.com>
Change-Id: I81c2cef4076487df1dd0ee75449dcb2371ac1dbc
(cherry picked from commit ac4488815518c236e60c0048833c51a76404b1b6)
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 05073d7..d95115a 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -35,51 +35,6 @@
#include "internal.h"
-/* Determine whether we can avoid taking write faults for known dirty pages. */
-static bool may_avoid_write_fault(pte_t pte, struct vm_area_struct *vma,
- unsigned long cp_flags)
-{
- /*
- * The dirty accountable bit indicates that we can always make the page
- * writable regardless of the number of references.
- */
- if (!(cp_flags & MM_CP_DIRTY_ACCT)) {
- /* Otherwise, we must have exclusive access to the page. */
- if (!(vma_is_anonymous(vma) && (vma->vm_flags & VM_WRITE)))
- return false;
-
- if (page_count(pte_page(pte)) != 1)
- return false;
- }
-
- /*
- * Don't do this optimization for clean pages as we need to be notified
- * of the transition from clean to dirty.
- */
- if (!pte_dirty(pte))
- return false;
-
- /* Same for softdirty. */
- if (!pte_soft_dirty(pte) && (vma->vm_flags & VM_SOFTDIRTY))
- return false;
-
- /*
- * For userfaultfd the user program needs to monitor write faults so we
- * can't do this optimization.
- */
- if (pte_uffd_wp(pte))
- return false;
-
- /*
- * It is unclear whether this optimization can be done safely for NUMA
- * pages.
- */
- if (cp_flags & MM_CP_PROT_NUMA)
- return false;
-
- return true;
-}
-
static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot,
unsigned long cp_flags)
@@ -88,6 +43,7 @@
spinlock_t *ptl;
unsigned long pages = 0;
int target_node = NUMA_NO_NODE;
+ bool dirty_accountable = cp_flags & MM_CP_DIRTY_ACCT;
bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
@@ -175,8 +131,12 @@
ptent = pte_clear_uffd_wp(ptent);
}
- if (may_avoid_write_fault(ptent, vma, cp_flags))
+ /* Avoid taking write faults for known dirty pages */
+ if (dirty_accountable && pte_dirty(ptent) &&
+ (pte_soft_dirty(ptent) ||
+ !(vma->vm_flags & VM_SOFTDIRTY))) {
ptent = pte_mkwrite(ptent);
+ }
ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
pages++;
} else if (is_swap_pte(oldpte)) {
