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Revert "FROMGIT: mm: improve mprotect(R|W) efficiency on pages referenced once"

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This reverts commit b44e46bb04.

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
This commit is contained in:
Peter Collingbourne 2022-01-05 10:58:25 -08:00 committed by Suren Baghdasaryan
parent 3a624c9ccd
commit ac44888155
1 changed files with 6 additions and 46 deletions
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52
mm/mprotect.c
View File

@ -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 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
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 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
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)) {