Maintaining Mlocked was the difficult one, but now that it is correctly
tracked, without duplication between the 4kB and 2MB amounts, I think
we have to make a similar effort with Mapped.
But whereas mlock and munlock were already rare and slow operations,
to which we could fairly add a little more overhead in the huge tmpfs
case, ordinary mmap is not something we want to slow down further,
relative to hugetlbfs.
In the Mapped case, I think we can take small or misaligned mmaps of
huge tmpfs files as the exceptional operation, and add a little more
overhead to those, by maintaining another count for them in the head;
and by keeping both hugely and unhugely mapped counts in the one long,
can rely on cmpxchg to manage their racing transitions atomically.
That's good on 64-bit, but there are not enough free bits in a 32-bit
atomic_long_t team_usage to support this: I think we should continue
to permit huge tmpfs on 32-bit, but accept that Mapped may be doubly
counted there. (A more serious problem on 32-bit is that it would,
I think, be possible to overflow the huge mapping counter: protection
against that will need to be added.)
Now that we are maintaining NR_FILE_MAPPED correctly for huge
tmpfs, adjust vmscan's zone_unmapped_file_pages() to exclude
NR_SHMEM_PMDMAPPED, which it clearly would not want included.
Whereas minimum_image_size() in kernel/power/snapshot.c? I have
not grasped the basis for that calculation, so leaving untouched.
Signed-off-by: Hugh Dickins <hu...@google.com>
---
include/linux/memcontrol.h | 5 +
include/linux/pageteam.h | 144 ++++++++++++++++++++++++++++++++---
mm/huge_memory.c | 34 +++++++-
mm/rmap.c | 10 +-
mm/vmscan.c | 6 +
5 files changed, 180 insertions(+), 19 deletions(-)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -700,6 +700,11 @@ static inline bool mem_cgroup_oom_synchr
return false;
}
+static inline void mem_cgroup_update_page_stat(struct page *page,
+ enum mem_cgroup_stat_index idx, int val)
+{
+}
+
static inline void mem_cgroup_inc_page_stat(struct page *page,
enum mem_cgroup_stat_index idx)
{
--- a/include/linux/pageteam.h
+++ b/include/linux/pageteam.h
@@ -30,6 +30,30 @@ static inline struct page *team_head(str
}
/*
+ * Layout of team head's page->team_usage field, as on x86_64 and arm64_4K:
+ *
+ * 63 32 31 22 21 12 11 10 9 0
+ * +------------+--------------+----------+----------+---------+------------+
+ * | pmd_mapped & instantiated |pte_mapped| reserved | mlocked | lru_weight |
+ * | 42 bits 10 bits | 10 bits | 1 bit | 1 bit | 10 bits |
+ * +------------+--------------+----------+----------+---------+------------+
+ *
+ * TEAM_LRU_WEIGHT_ONE 1 (1<<0)
+ * TEAM_LRU_WEIGHT_MASK 3ff (1<<10)-1
+ * TEAM_PMD_MLOCKED 400 (1<<10)
+ * TEAM_RESERVED_FLAG 800 (1<<11)
+ * TEAM_PTE_COUNTER 1000 (1<<12)
+ * TEAM_PTE_MASK 3ff000 (1<<22)-(1<<12)
+ * TEAM_PAGE_COUNTER 400000 (1<<22)
+ * TEAM_COMPLETE 80000000 (1<<31)
+ * TEAM_MAPPING_COUNTER 400000 (1<<22)
+ * TEAM_PMD_MAPPED 80400000 (1<<31)
+ *
+ * The upper bits count up to TEAM_COMPLETE as pages are instantiated,
+ * and then, above TEAM_COMPLETE, they count huge mappings of the team.
+ * Team tails have team_usage either 1 (lru_weight 1) or 0 (lru_weight 0).
+ */
+/*
* Mask for lower bits of team_usage, giving the weight 0..HPAGE_PMD_NR of the
* page on its LRU: normal pages have weight 1, tails held unevictable until
* head is evicted have weight 0, and the head gathers weight 1..HPAGE_PMD_NR.
@@ -42,8 +66,22 @@ static inline struct page *team_head(str
*/
#define TEAM_PMD_MLOCKED (1L << (HPAGE_PMD_ORDER + 1))
#define TEAM_RESERVED_FLAG (1L << (HPAGE_PMD_ORDER + 2))
-
+#ifdef CONFIG_64BIT
+/*
+ * Count how many pages of team are individually mapped into userspace.
+ */
+#define TEAM_PTE_COUNTER (1L << (HPAGE_PMD_ORDER + 3))
+#define TEAM_HIGH_COUNTER (1L << (2*HPAGE_PMD_ORDER + 4))
+#define TEAM_PTE_MASK (TEAM_HIGH_COUNTER - TEAM_PTE_COUNTER)
+#define team_pte_count(usage) (((usage) & TEAM_PTE_MASK) / TEAM_PTE_COUNTER)
+#else /* 32-bit */
+/*
+ * Not enough bits in atomic_long_t: we prefer not to bloat struct page just to
+ * avoid duplication in Mapped, when a page is mapped both hugely and unhugely.
+ */
#define TEAM_HIGH_COUNTER (1L << (HPAGE_PMD_ORDER + 3))
+#define team_pte_count(usage) 1 /* allows for the extra page_add_file_rmap */
+#endif /* CONFIG_64BIT */
/*
* Count how many pages of team are instantiated, as it is built up.
*/
@@ -66,22 +104,110 @@ static inline bool team_pmd_mapped(struc
/*
* Returns true if this was the first mapping by pmd, whereupon mapped stats
- * need to be updated.
+ * need to be updated. Together with the number of pages which then need
+ * to be accounted (can be ignored when false returned): because some team
+ * members may have been mapped unhugely by pte, so already counted as Mapped.
*/
-static inline bool inc_team_pmd_mapped(struct page *head)
+static inline bool inc_team_pmd_mapped(struct page *head, int *nr_pages)
{
- return atomic_long_add_return(TEAM_MAPPING_COUNTER, &head->team_usage)
- < TEAM_PMD_MAPPED + TEAM_MAPPING_COUNTER;
+ long team_usage;
+
+ team_usage = atomic_long_add_return(TEAM_MAPPING_COUNTER,
+ &head->team_usage);
+ *nr_pages = HPAGE_PMD_NR - team_pte_count(team_usage);
+ return team_usage < TEAM_PMD_MAPPED + TEAM_MAPPING_COUNTER;
}
/*
* Returns true if this was the last mapping by pmd, whereupon mapped stats
- * need to be updated.
+ * need to be updated. Together with the number of pages which then need
+ * to be accounted (can be ignored when false returned): because some team
+ * members may still be mapped unhugely by pte, so remain counted as Mapped.
+ */
+static inline bool dec_team_pmd_mapped(struct page *head, int *nr_pages)
+{
+ long team_usage;
+
+ team_usage = atomic_long_sub_return(TEAM_MAPPING_COUNTER,
+ &head->team_usage);
+ *nr_pages = HPAGE_PMD_NR - team_pte_count(team_usage);
+ return team_usage < TEAM_PMD_MAPPED;
+}
+
+/*
+ * Returns true if this pte mapping is of a non-team page, or of a team page
not
+ * covered by an existing huge pmd mapping: whereupon stats need to be updated.
+ * Only called when mapcount goes up from 0 to 1 i.e. _mapcount from -1 to 0.
+ */
+static inline bool inc_team_pte_mapped(struct page *page)
+{
+#ifdef CONFIG_64BIT
+ struct page *head;
+ long team_usage;
+ long old;
+
+ if (likely(!PageTeam(page)))
+ return true;
+ head = team_head(page);
+ team_usage = atomic_long_read(&head->team_usage);
+ for (;;) {
+ /* Is team now being disbanded? Stop once team_usage is reset */
+ if (unlikely(!PageTeam(head) ||
+ team_usage / TEAM_PAGE_COUNTER == 0))
+ return true;
+ /*
+ * XXX: but despite the impressive-looking cmpxchg, gthelen
+ * points out that head might be freed and reused and assigned
+ * a matching value in ->private now: tiny chance, must revisit.
+ */
+ old = atomic_long_cmpxchg(&head->team_usage,
+ team_usage, team_usage + TEAM_PTE_COUNTER);
+ if (likely(old == team_usage))
+ break;
+ team_usage = old;
+ }
+ return team_usage < TEAM_PMD_MAPPED;
+#else /* 32-bit */
+ return true;
+#endif
+}
+
+/*
+ * Returns true if this pte mapping is of a non-team page, or of a team page
not
+ * covered by a remaining huge pmd mapping: whereupon stats need to be updated.
+ * Only called when mapcount goes down from 1 to 0 i.e. _mapcount from 0 to -1.
*/
-static inline bool dec_team_pmd_mapped(struct page *head)
+static inline bool dec_team_pte_mapped(struct page *page)
{
- return atomic_long_sub_return(TEAM_MAPPING_COUNTER, &head->team_usage)
- < TEAM_PMD_MAPPED;
+#ifdef CONFIG_64BIT
+ struct page *head;
+ long team_usage;
+ long old;
+
+ if (likely(!PageTeam(page)))
+ return true;
+ head = team_head(page);
+ team_usage = atomic_long_read(&head->team_usage);
+ for (;;) {
+ /* Is team now being disbanded? Stop once team_usage is reset */
+ if (unlikely(!PageTeam(head) ||
+ team_usage / TEAM_PAGE_COUNTER == 0))
+ return true;
+ /*
+ * XXX: but despite the impressive-looking cmpxchg, gthelen
+ * points out that head might be freed and reused and assigned
+ * a matching value in ->private now: tiny chance, must revisit.
+ */
+ old = atomic_long_cmpxchg(&head->team_usage,
+ team_usage, team_usage - TEAM_PTE_COUNTER);
+ if (likely(old == team_usage))
+ break;
+ team_usage = old;
+ }
+ return team_usage < TEAM_PMD_MAPPED;
+#else /* 32-bit */
+ return true;
+#endif
}
static inline void inc_lru_weight(struct page *head)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1130,9 +1130,11 @@ int copy_huge_pmd(struct mm_struct *dst_
pmdp_set_wrprotect(src_mm, addr, src_pmd);
pmd = pmd_wrprotect(pmd);
} else {
+ int nr_pages; /* not interesting here */
+
VM_BUG_ON_PAGE(!PageTeam(src_page), src_page);
page_dup_rmap(src_page, false);
- inc_team_pmd_mapped(src_page);
+ inc_team_pmd_mapped(src_page, &nr_pages);
}
add_mm_counter(dst_mm, mm_counter(src_page), HPAGE_PMD_NR);
atomic_long_inc(&dst_mm->nr_ptes);
@@ -3499,18 +3501,40 @@ late_initcall(split_huge_pages_debugfs);
static void page_add_team_rmap(struct page *page)
{
+ int nr_pages;
+
VM_BUG_ON_PAGE(PageAnon(page), page);
VM_BUG_ON_PAGE(!PageTeam(page), page);
- if (inc_team_pmd_mapped(page))
- __inc_zone_page_state(page, NR_SHMEM_PMDMAPPED);
+
+ lock_page_memcg(page);
+ if (inc_team_pmd_mapped(page, &nr_pages)) {
+ struct zone *zone = page_zone(page);
+
+ __inc_zone_state(zone, NR_SHMEM_PMDMAPPED);
+ __mod_zone_page_state(zone, NR_FILE_MAPPED, nr_pages);
+ mem_cgroup_update_page_stat(page,
+ MEM_CGROUP_STAT_FILE_MAPPED, nr_pages);
+ }
+ unlock_page_memcg(page);
}
static void page_remove_team_rmap(struct page *page)
{
+ int nr_pages;
+
VM_BUG_ON_PAGE(PageAnon(page), page);
VM_BUG_ON_PAGE(!PageTeam(page), page);
- if (dec_team_pmd_mapped(page))
- __dec_zone_page_state(page, NR_SHMEM_PMDMAPPED);
+
+ lock_page_memcg(page);
+ if (dec_team_pmd_mapped(page, &nr_pages)) {
+ struct zone *zone = page_zone(page);
+
+ __dec_zone_state(zone, NR_SHMEM_PMDMAPPED);
+ __mod_zone_page_state(zone, NR_FILE_MAPPED, -nr_pages);
+ mem_cgroup_update_page_stat(page,
+ MEM_CGROUP_STAT_FILE_MAPPED, -nr_pages);
+ }
+ unlock_page_memcg(page);
}
int map_team_by_pmd(struct vm_area_struct *vma, unsigned long addr,
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1272,7 +1272,8 @@ void page_add_new_anon_rmap(struct page
void page_add_file_rmap(struct page *page)
{
lock_page_memcg(page);
- if (atomic_inc_and_test(&page->_mapcount)) {
+ if (atomic_inc_and_test(&page->_mapcount) &&
+ inc_team_pte_mapped(page)) {
__inc_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
}
@@ -1299,9 +1300,10 @@ static void page_remove_file_rmap(struct
* 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);
- mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
-
+ if (dec_team_pte_mapped(page)) {
+ __dec_zone_page_state(page, NR_FILE_MAPPED);
+ mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
+ }
if (unlikely(PageMlocked(page)))
clear_page_mlock(page);
out:
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3685,8 +3685,12 @@ static inline unsigned long zone_unmappe
/*
* It's possible for there to be more file mapped pages than
* accounted for by the pages on the file LRU lists because
- * tmpfs pages accounted for as ANON can also be FILE_MAPPED
+ * tmpfs pages accounted for as ANON can also be FILE_MAPPED.
+ * We don't know how many, beyond the PMDMAPPED excluded below.
*/
+ if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+ file_mapped -= zone_page_state(zone, NR_SHMEM_PMDMAPPED) <<
+ HPAGE_PMD_ORDER;
return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}
