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mm: do_wp_page() simplification

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How about we just make sure we're the only possible valid user fo the
page before we bother to reuse it?

Simplify, simplify, simplify.

And get rid of the nasty serialization on the page lock at the same time.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[peterx: add subject prefix]
Signed-off-by: Peter Xu <peterx@redhat.com>
Git-commit: 09854ba94c6aad7886996bfbee2530b3d8a7f4f4
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
[zhenhuah@codeaurora.org: resolve trivial merge conflicts]
Change-Id: I73dc102cb02d751d497bdf3cc39179a4bfdc5a54
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>
This commit is contained in:
Linus Torvalds 2020-08-21 19:49:55 -04:00 • committed by Zhenhua Huang
commit f63da7afd7
1 changed files with 17 additions and 44 deletions
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61
mm/memory.c
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@ -2755,52 +2755,25 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
* not dirty accountable.
*/
if (PageAnon(vmf->page)) {
int total_map_swapcount;
if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) ||
page_count(vmf->page) != 1))
struct page *page = vmf->page;
/* PageKsm() doesn't necessarily raise the page refcount */
if (PageKsm(page) || page_count(page) != 1)
goto copy;
if (!trylock_page(page))
goto copy;
if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {
unlock_page(page);
goto copy;
if (!trylock_page(vmf->page)) {
get_page(vmf->page);
pte_unmap_unlock(vmf->pte, vmf->ptl);
lock_page(vmf->page);
if (!pte_map_lock(vmf)) {
unlock_page(vmf->page);
put_page(vmf->page);
return VM_FAULT_RETRY;
}
if (!pte_same(*vmf->pte, vmf->orig_pte)) {
unlock_page(vmf->page);
pte_unmap_unlock(vmf->pte, vmf->ptl);
put_page(vmf->page);
return 0;
}
put_page(vmf->page);
}
if (PageKsm(vmf->page)) {
bool reused = reuse_ksm_page(vmf->page, vmf->vma,
vmf->address);
unlock_page(vmf->page);
if (!reused)
goto copy;
wp_page_reuse(vmf);
return VM_FAULT_WRITE;
}
if (reuse_swap_page(vmf->page, &total_map_swapcount)) {
if (total_map_swapcount == 1) {
/*
* The page is all ours. Move it to
* our anon_vma so the rmap code will
* not search our parent or siblings.
* Protected against the rmap code by
* the page lock.
*/
page_move_anon_rmap(vmf->page, vma);
}
unlock_page(vmf->page);
wp_page_reuse(vmf);
return VM_FAULT_WRITE;
}
unlock_page(vmf->page);
/*
* Ok, we've got the only map reference, and the only
* page count reference, and the page is locked,
* it's dark out, and we're wearing sunglasses. Hit it.
*/
wp_page_reuse(vmf);
unlock_page(page);
return VM_FAULT_WRITE;
} else if (unlikely((vmf->vma_flags & (VM_WRITE|VM_SHARED)) ==
(VM_WRITE|VM_SHARED))) {
return wp_page_shared(vmf);