Skip to content

Commit

Permalink
mm: do_wp_page() simplification
Browse files Browse the repository at this point in the history
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.

[peterx: add subject prefix]

Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Peter Xu <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
  • Loading branch information
torvalds committed Sep 4, 2020
1 parent bcf8768 commit 09854ba
Showing 1 changed file with 17 additions and 42 deletions.
59 changes: 17 additions & 42 deletions mm/memory.c
Original file line number Diff line number Diff line change
Expand Up @@ -2924,50 +2924,25 @@ 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);
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
vmf->address, &vmf->ptl);
if (!pte_same(*vmf->pte, vmf->orig_pte)) {
update_mmu_tlb(vma, vmf->address, vmf->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((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
(VM_WRITE|VM_SHARED))) {
return wp_page_shared(vmf);
Expand Down

0 comments on commit 09854ba

Please sign in to comment.