Naive approach: on mapping/unmapping the page as compound we update
->_mapcount on each 4k page. That's not efficient, but it's not obvious
how we can optimize this. We can look into optimization later.
PG_double_map optimization doesn't work for file pages since lifecycle
of file pages is different comparing to anon pages: file page can be
mapped again at any time.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 2 +-
mm/huge_memory.c | 10 +++++++---
mm/memory.c | 4 ++--
mm/migrate.c | 2 +-
mm/rmap.c | 48 +++++++++++++++++++++++++++++++++++-------------
mm/util.c | 6 ++++++
6 files changed, 52 insertions(+), 20 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 49eb4f8ebac9..5704f101b52e 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -165,7 +165,7 @@ void do_page_add_anon_rmap(struct page *, struct vm_area_struct *,
unsigned long, int);
void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
unsigned long, bool);
-void page_add_file_rmap(struct page *);
+void page_add_file_rmap(struct page *, bool);
void page_remove_rmap(struct page *, bool);
void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f2f255610a7c..dcd2229277be 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3315,18 +3315,22 @@ static void __split_huge_page(struct page *page, struct list_head *list)
int total_mapcount(struct page *page)
{
- int i, ret;
+ int i, compound, ret;
VM_BUG_ON_PAGE(PageTail(page), page);
if (likely(!PageCompound(page)))
return atomic_read(&page->_mapcount) + 1;
- ret = compound_mapcount(page);
+ compound = compound_mapcount(page);
if (PageHuge(page))
- return ret;
+ return compound;
+ ret = compound;
for (i = 0; i < HPAGE_PMD_NR; i++)
ret += atomic_read(&page[i]._mapcount) + 1;
+ /* File pages has compound_mapcount included in _mapcount */
+ if (!PageAnon(page))
+ return ret - compound * HPAGE_PMD_NR;
if (PageDoubleMap(page))
ret -= HPAGE_PMD_NR;
return ret;
diff --git a/mm/memory.c b/mm/memory.c
index 113ac4884c4e..ea9e4871e4e3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1494,7 +1494,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
/* Ok, finally just insert the thing.. */
get_page(page);
inc_mm_counter_fast(mm, mm_counter_file(page));
- page_add_file_rmap(page);
+ page_add_file_rmap(page, false);
set_pte_at(mm, addr, pte, mk_pte(page, prot));
retval = 0;
@@ -2965,7 +2965,7 @@ int alloc_set_pte(struct fault_env *fe, struct mem_cgroup *memcg,
lru_cache_add_active_or_unevictable(page, vma);
} else {
inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
- page_add_file_rmap(page);
+ page_add_file_rmap(page, false);
}
set_pte_at(vma->vm_mm, fe->address, fe->pte, entry);
diff --git a/mm/migrate.c b/mm/migrate.c
index e6daf49e224f..7e6e9375d654 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -259,7 +259,7 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
} else if (PageAnon(new))
page_add_anon_rmap(new, vma, addr, false);
else
- page_add_file_rmap(new);
+ page_add_file_rmap(new, false);
if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
mlock_vma_page(new);
diff --git a/mm/rmap.c b/mm/rmap.c
index 0ea5d9071b32..b78374519bac 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1273,18 +1273,34 @@ void page_add_new_anon_rmap(struct page *page,
*
* The caller needs to hold the pte lock.
*/
-void page_add_file_rmap(struct page *page)
+void page_add_file_rmap(struct page *page, bool compound)
{
+ int i, nr = 1;
+
+ VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
lock_page_memcg(page);
- if (atomic_inc_and_test(&page->_mapcount)) {
- __inc_zone_page_state(page, NR_FILE_MAPPED);
- mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
+ if (compound && PageTransHuge(page)) {
+ for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
+ if (atomic_inc_and_test(&page[i]._mapcount))
+ nr++;
+ }
+ if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
+ goto out;
+ } else {
+ if (!atomic_inc_and_test(&page->_mapcount))
+ goto out;
}
+ __mod_zone_page_state(page_zone(page), NR_FILE_MAPPED, nr);
+ mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
+out:
unlock_page_memcg(page);
}
-static void page_remove_file_rmap(struct page *page)
+static void page_remove_file_rmap(struct page *page, bool compound)
{
+ int i, nr = 1;
+
+ VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
lock_page_memcg(page);
/* Hugepages are not counted in NR_FILE_MAPPED for now. */
@@ -1295,15 +1311,24 @@ static void page_remove_file_rmap(struct page *page)
}
/* page still mapped by someone else? */
- if (!atomic_add_negative(-1, &page->_mapcount))
- goto out;
+ if (compound && PageTransHuge(page)) {
+ for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
+ if (atomic_add_negative(-1, &page[i]._mapcount))
+ nr++;
+ }
+ if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
+ goto out;
+ } else {
+ if (!atomic_add_negative(-1, &page->_mapcount))
+ goto out;
+ }
/*
* We use the irq-unsafe __{inc|mod}_zone_page_stat because
* these counters are not modified in interrupt context, and
* pte lock(a spinlock) is held, which implies preemption disabled.
*/
- __dec_zone_page_state(page, NR_FILE_MAPPED);
+ __mod_zone_page_state(page_zone(page), NR_FILE_MAPPED, -nr);
mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
if (unlikely(PageMlocked(page)))
@@ -1359,11 +1384,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
*/
void page_remove_rmap(struct page *page, bool compound)
{
- if (!PageAnon(page)) {
- VM_BUG_ON_PAGE(compound && !PageHuge(page), page);
- page_remove_file_rmap(page);
- return;
- }
+ if (!PageAnon(page))
+ return page_remove_file_rmap(page, compound);
if (compound)
return page_remove_anon_compound_rmap(page);
diff --git a/mm/util.c b/mm/util.c
index b756ee36f7f0..8d010ef2ce1c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -412,6 +412,12 @@ int __page_mapcount(struct page *page)
int ret;
ret = atomic_read(&page->_mapcount) + 1;
+ /*
+ * For file THP page->_mapcount contains total number of mapping
+ * of the page: no need to look into compound_mapcount.
+ */
+ if (!PageAnon(page) && !PageHuge(page))
+ return ret;
page = compound_head(page);
ret += atomic_read(compound_mapcount_ptr(page)) + 1;
if (PageDoubleMap(page))
--
2.8.1
--
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