This will allow the mm code to figure out when a file has been
changed through a writable mmap. Future changes will use this
information to update the file timestamp after writes.
This is handled in core mm code for two reasons:
1. Performance. Setting a bit directly is faster than an indirect
call to a vma op.
2. Simplicity. The cmtime bit is set with lots of mm locks held.
Rather than making filesystems add a new vm operation that needs
to be aware of locking, it's easier to just get it right in core
code.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
include/linux/pagemap.h | 16 ++++++++++++++++
mm/memory.c | 7 ++++++-
mm/rmap.c | 27 +++++++++++++++++++++++++--
3 files changed, 47 insertions(+), 3 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e3dea75..9a461ee 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -25,6 +25,7 @@ enum mapping_flags {
AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */
+ AS_CMTIME = __GFP_BITS_SHIFT + 5, /* cmtime update deferred */
};
static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -74,6 +75,21 @@ static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
}
+static inline void mapping_set_cmtime(struct address_space * mapping)
+{
+ set_bit(AS_CMTIME, &mapping->flags);
+}
+
+static inline bool mapping_test_cmtime(struct address_space * mapping)
+{
+ return test_bit(AS_CMTIME, &mapping->flags);
+}
+
+static inline bool mapping_test_clear_cmtime(struct address_space * mapping)
+{
+ return test_and_clear_bit(AS_CMTIME, &mapping->flags);
+}
+
/*
* This is non-atomic. Only to be used before the mapping is activated.
* Probably needs a barrier...
diff --git a/mm/memory.c b/mm/memory.c
index 4026841..1737a90 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1150,8 +1150,13 @@ again:
if (PageAnon(page))
rss[MM_ANONPAGES]--;
else {
- if (pte_dirty(ptent))
+ if (pte_dirty(ptent)) {
+ struct address_space *mapping =
+ page_mapping(page);
+ if (mapping)
+ mapping_set_cmtime(mapping);
set_page_dirty(page);
+ }
if (pte_young(ptent) &&
likely(!(vma->vm_flags & VM_SEQ_READ)))
mark_page_accessed(page);
diff --git a/mm/rmap.c b/mm/rmap.c
index b2e29ac..2e3fb27 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -928,6 +928,10 @@ static int page_mkclean_file(struct address_space *mapping, struct page *page)
}
}
mutex_unlock(&mapping->i_mmap_mutex);
+
+ if (ret)
+ mapping_set_cmtime(mapping);
+
return ret;
}
@@ -1179,6 +1183,19 @@ out:
}
/*
+ * Mark a page's mapping for future cmtime update. It's safe to call this
+ * on any page, but it only has any effect if the page is backed by a mapping
+ * that uses mapping_test_clear_cmtime to handle file time updates. This means
+ * that there's no need to call this on for non-VM_SHARED vmas.
+ */
+static void page_set_cmtime(struct page *page)
+{
+ struct address_space *mapping = page_mapping(page);
+ if (mapping)
+ mapping_set_cmtime(mapping);
+}
+
+/*
* Subfunctions of try_to_unmap: try_to_unmap_one called
* repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
*/
@@ -1219,8 +1236,11 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
pteval = ptep_clear_flush(vma, address, pte);
/* Move the dirty bit to the physical page now the pte is gone. */
- if (pte_dirty(pteval))
+ if (pte_dirty(pteval)) {
set_page_dirty(page);
+ if (vma->vm_flags & VM_SHARED)
+ page_set_cmtime(page);
+ }
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
@@ -1413,8 +1433,11 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
}
/* Move the dirty bit to the physical page now the pte is gone. */
- if (pte_dirty(pteval))
+ if (pte_dirty(pteval)) {
set_page_dirty(page);
+ if (vma->vm_flags & VM_SHARED)
+ page_set_cmtime(page);
+ }
page_remove_rmap(page);
page_cache_release(page);
--
1.8.3.1
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