[PATCH v2 4/5] mm: Add zap_skip_check_mapping() helper

Peter Xu
2021-09-02T20:18:27Z

Use the helper for the checks. Rename "check_mapping" into "zap_mapping"
because "check_mapping" looks like a bool but in fact it stores the mapping
itself. When it's set, we check the mapping (it must be non-NULL). When it's
cleared we skip the check, which works like the old way.

Move the duplicated comments to the helper too.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
include/linux/mm.h | 15 ++++++++++++++-
mm/memory.c | 29 ++++++-----------------------
2 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69259229f090..81e402a5fbc9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1720,10 +1720,23 @@ extern void user_shm_unlock(size_t, struct ucounts *);
* Parameter block passed down to zap_pte_range in exceptional cases.
*/
struct zap_details {
- struct address_space *check_mapping; /* Check page->mapping if set */
+ struct address_space *zap_mapping; /* Check page->mapping if set */
struct page *single_page; /* Locked page to be unmapped */
};

+/*
+ * We set details->zap_mappings when we want to unmap shared but keep private
+ * pages. Return true if skip zapping this page, false otherwise.
+ */
+static inline bool
+zap_skip_check_mapping(struct zap_details *details, struct page *page)
+{
+ if (!details || !page)
+ return false;
+
+ return details->zap_mapping != page_rmapping(page);
+}
+
struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
pte_t pte);
struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index 6bba3b9fef7c..e5ee8399d270 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1333,16 +1333,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
struct page *page;

page = vm_normal_page(vma, addr, ptent);
- if (unlikely(details) && page) {
- /*
- * unmap_shared_mapping_pages() wants to
- * invalidate cache without truncating:
- * unmap shared but keep private pages.
- */
- if (details->check_mapping &&
- details->check_mapping != page_rmapping(page))
- continue;
- }
+ if (unlikely(zap_skip_check_mapping(details, page)))
+ continue;
ptent = ptep_get_and_clear_full(mm, addr, pte,
tlb->fullmm);
tlb_remove_tlb_entry(tlb, pte, addr);
@@ -1375,17 +1367,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
is_device_exclusive_entry(entry)) {
struct page *page = pfn_swap_entry_to_page(entry);

- if (unlikely(details && details->check_mapping)) {
- /*
- * unmap_shared_mapping_pages() wants to
- * invalidate cache without truncating:
- * unmap shared but keep private pages.
- */
- if (details->check_mapping !=
- page_rmapping(page))
- continue;
- }
-
+ if (unlikely(zap_skip_check_mapping(details, page)))
+ continue;
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
rss[mm_counter(page)]--;

@@ -3368,7 +3351,7 @@ void unmap_mapping_page(struct page *page)
first_index = page->index;
last_index = page->index + thp_nr_pages(page) - 1;

- details.check_mapping = mapping;
+ details.zap_mapping = mapping;
details.single_page = page;

i_mmap_lock_write(mapping);
@@ -3396,7 +3379,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
pgoff_t first_index = start, last_index = start + nr - 1;
struct zap_details details = { };

- details.check_mapping = even_cows ? NULL : mapping;
+ details.zap_mapping = even_cows ? NULL : mapping;
if (last_index < first_index)
last_index = ULONG_MAX;

--
2.31.1