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-rw-r--r--include/linux/mm_types.h49
-rw-r--r--include/linux/page-flags.h4
-rw-r--r--include/linux/rmap.h165
3 files changed, 218 insertions, 0 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9499eb8e8e66..aac7c87b04e1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -292,6 +292,44 @@ typedef struct {
#define NR_PAGES_IN_LARGE_FOLIO
#endif
+/*
+ * On 32bit, we can cut the required metadata in half, because:
+ * (a) PID_MAX_LIMIT implicitly limits the number of MMs we could ever have,
+ * so we can limit MM IDs to 15 bit (32767).
+ * (b) We don't expect folios where even a single complete PTE mapping by
+ * one MM would exceed 15 bits (order-15).
+ */
+#ifdef CONFIG_64BIT
+typedef int mm_id_mapcount_t;
+#define MM_ID_MAPCOUNT_MAX INT_MAX
+typedef unsigned int mm_id_t;
+#else /* !CONFIG_64BIT */
+typedef short mm_id_mapcount_t;
+#define MM_ID_MAPCOUNT_MAX SHRT_MAX
+typedef unsigned short mm_id_t;
+#endif /* CONFIG_64BIT */
+
+/* We implicitly use the dummy ID for init-mm etc. where we never rmap pages. */
+#define MM_ID_DUMMY 0
+#define MM_ID_MIN (MM_ID_DUMMY + 1)
+
+/*
+ * We leave the highest bit of each MM id unused, so we can store a flag
+ * in the highest bit of each folio->_mm_id[].
+ */
+#define MM_ID_BITS ((sizeof(mm_id_t) * BITS_PER_BYTE) - 1)
+#define MM_ID_MASK ((1U << MM_ID_BITS) - 1)
+#define MM_ID_MAX MM_ID_MASK
+
+/*
+ * In order to use bit_spin_lock(), which requires an unsigned long, we
+ * operate on folio->_mm_ids when working on flags.
+ */
+#define FOLIO_MM_IDS_LOCK_BITNUM MM_ID_BITS
+#define FOLIO_MM_IDS_LOCK_BIT BIT(FOLIO_MM_IDS_LOCK_BITNUM)
+#define FOLIO_MM_IDS_SHARED_BITNUM (2 * MM_ID_BITS + 1)
+#define FOLIO_MM_IDS_SHARED_BIT BIT(FOLIO_MM_IDS_SHARED_BITNUM)
+
/**
* struct folio - Represents a contiguous set of bytes.
* @flags: Identical to the page flags.
@@ -318,6 +356,9 @@ typedef struct {
* @_nr_pages_mapped: Do not use outside of rmap and debug code.
* @_pincount: Do not use directly, call folio_maybe_dma_pinned().
* @_nr_pages: Do not use directly, call folio_nr_pages().
+ * @_mm_id: Do not use outside of rmap code.
+ * @_mm_ids: Do not use outside of rmap code.
+ * @_mm_id_mapcount: Do not use outside of rmap code.
* @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
* @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
* @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
@@ -390,6 +431,11 @@ struct folio {
atomic_t _entire_mapcount;
atomic_t _pincount;
#endif /* CONFIG_64BIT */
+ mm_id_mapcount_t _mm_id_mapcount[2];
+ union {
+ mm_id_t _mm_id[2];
+ unsigned long _mm_ids;
+ };
/* private: the union with struct page is transitional */
};
unsigned long _usable_1[4];
@@ -1114,6 +1160,9 @@ struct mm_struct {
#endif
} lru_gen;
#endif /* CONFIG_LRU_GEN_WALKS_MMU */
+#ifdef CONFIG_MM_ID
+ mm_id_t mm_id;
+#endif /* CONFIG_MM_ID */
} __randomize_layout;
/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index cab382bd965e..f26ce54c7aa4 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1185,6 +1185,10 @@ static inline int folio_has_private(const struct folio *folio)
return !!(folio->flags & PAGE_FLAGS_PRIVATE);
}
+static inline bool folio_test_large_maybe_mapped_shared(const struct folio *folio)
+{
+ return test_bit(FOLIO_MM_IDS_SHARED_BITNUM, &folio->_mm_ids);
+}
#undef PF_ANY
#undef PF_HEAD
#undef PF_NO_TAIL
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index d1e888cc97a5..c131b0efff0f 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -13,6 +13,7 @@
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/memremap.h>
+#include <linux/bit_spinlock.h>
/*
* The anon_vma heads a list of private "related" vmas, to scan if
@@ -173,6 +174,169 @@ static inline void anon_vma_merge(struct vm_area_struct *vma,
struct anon_vma *folio_get_anon_vma(const struct folio *folio);
+#ifdef CONFIG_MM_ID
+static __always_inline void folio_lock_large_mapcount(struct folio *folio)
+{
+ bit_spin_lock(FOLIO_MM_IDS_LOCK_BITNUM, &folio->_mm_ids);
+}
+
+static __always_inline void folio_unlock_large_mapcount(struct folio *folio)
+{
+ __bit_spin_unlock(FOLIO_MM_IDS_LOCK_BITNUM, &folio->_mm_ids);
+}
+
+static inline unsigned int folio_mm_id(const struct folio *folio, int idx)
+{
+ VM_WARN_ON_ONCE(idx != 0 && idx != 1);
+ return folio->_mm_id[idx] & MM_ID_MASK;
+}
+
+static inline void folio_set_mm_id(struct folio *folio, int idx, mm_id_t id)
+{
+ VM_WARN_ON_ONCE(idx != 0 && idx != 1);
+ folio->_mm_id[idx] &= ~MM_ID_MASK;
+ folio->_mm_id[idx] |= id;
+}
+
+static inline void __folio_large_mapcount_sanity_checks(const struct folio *folio,
+ int diff, mm_id_t mm_id)
+{
+ VM_WARN_ON_ONCE(!folio_test_large(folio) || folio_test_hugetlb(folio));
+ VM_WARN_ON_ONCE(diff <= 0);
+ VM_WARN_ON_ONCE(mm_id < MM_ID_MIN || mm_id > MM_ID_MAX);
+
+ /*
+ * Make sure we can detect at least one complete PTE mapping of the
+ * folio in a single MM as "exclusively mapped". This is primarily
+ * a check on 32bit, where we currently reduce the size of the per-MM
+ * mapcount to a short.
+ */
+ VM_WARN_ON_ONCE(diff > folio_large_nr_pages(folio));
+ VM_WARN_ON_ONCE(folio_large_nr_pages(folio) - 1 > MM_ID_MAPCOUNT_MAX);
+
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 0) == MM_ID_DUMMY &&
+ folio->_mm_id_mapcount[0] != -1);
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 0) != MM_ID_DUMMY &&
+ folio->_mm_id_mapcount[0] < 0);
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 1) == MM_ID_DUMMY &&
+ folio->_mm_id_mapcount[1] != -1);
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 1) != MM_ID_DUMMY &&
+ folio->_mm_id_mapcount[1] < 0);
+ VM_WARN_ON_ONCE(!folio_mapped(folio) &&
+ folio_test_large_maybe_mapped_shared(folio));
+}
+
+static __always_inline void folio_set_large_mapcount(struct folio *folio,
+ int mapcount, struct vm_area_struct *vma)
+{
+ __folio_large_mapcount_sanity_checks(folio, mapcount, vma->vm_mm->mm_id);
+
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 0) != MM_ID_DUMMY);
+ VM_WARN_ON_ONCE(folio_mm_id(folio, 1) != MM_ID_DUMMY);
+
+ /* Note: mapcounts start at -1. */
+ atomic_set(&folio->_large_mapcount, mapcount - 1);
+ folio->_mm_id_mapcount[0] = mapcount - 1;
+ folio_set_mm_id(folio, 0, vma->vm_mm->mm_id);
+}
+
+static __always_inline void folio_add_large_mapcount(struct folio *folio,
+ int diff, struct vm_area_struct *vma)
+{
+ const mm_id_t mm_id = vma->vm_mm->mm_id;
+ int new_mapcount_val;
+
+ folio_lock_large_mapcount(folio);
+ __folio_large_mapcount_sanity_checks(folio, diff, mm_id);
+
+ new_mapcount_val = atomic_read(&folio->_large_mapcount) + diff;
+ atomic_set(&folio->_large_mapcount, new_mapcount_val);
+
+ /*
+ * If a folio is mapped more than once into an MM on 32bit, we
+ * can in theory overflow the per-MM mapcount (although only for
+ * fairly large folios), turning it negative. In that case, just
+ * free up the slot and mark the folio "mapped shared", otherwise
+ * we might be in trouble when unmapping pages later.
+ */
+ if (folio_mm_id(folio, 0) == mm_id) {
+ folio->_mm_id_mapcount[0] += diff;
+ if (!IS_ENABLED(CONFIG_64BIT) && unlikely(folio->_mm_id_mapcount[0] < 0)) {
+ folio->_mm_id_mapcount[0] = -1;
+ folio_set_mm_id(folio, 0, MM_ID_DUMMY);
+ folio->_mm_ids |= FOLIO_MM_IDS_SHARED_BIT;
+ }
+ } else if (folio_mm_id(folio, 1) == mm_id) {
+ folio->_mm_id_mapcount[1] += diff;
+ if (!IS_ENABLED(CONFIG_64BIT) && unlikely(folio->_mm_id_mapcount[1] < 0)) {
+ folio->_mm_id_mapcount[1] = -1;
+ folio_set_mm_id(folio, 1, MM_ID_DUMMY);
+ folio->_mm_ids |= FOLIO_MM_IDS_SHARED_BIT;
+ }
+ } else if (folio_mm_id(folio, 0) == MM_ID_DUMMY) {
+ folio_set_mm_id(folio, 0, mm_id);
+ folio->_mm_id_mapcount[0] = diff - 1;
+ /* We might have other mappings already. */
+ if (new_mapcount_val != diff - 1)
+ folio->_mm_ids |= FOLIO_MM_IDS_SHARED_BIT;
+ } else if (folio_mm_id(folio, 1) == MM_ID_DUMMY) {
+ folio_set_mm_id(folio, 1, mm_id);
+ folio->_mm_id_mapcount[1] = diff - 1;
+ /* Slot 0 certainly has mappings as well. */
+ folio->_mm_ids |= FOLIO_MM_IDS_SHARED_BIT;
+ }
+ folio_unlock_large_mapcount(folio);
+}
+
+static __always_inline void folio_sub_large_mapcount(struct folio *folio,
+ int diff, struct vm_area_struct *vma)
+{
+ const mm_id_t mm_id = vma->vm_mm->mm_id;
+ int new_mapcount_val;
+
+ folio_lock_large_mapcount(folio);
+ __folio_large_mapcount_sanity_checks(folio, diff, mm_id);
+
+ new_mapcount_val = atomic_read(&folio->_large_mapcount) - diff;
+ atomic_set(&folio->_large_mapcount, new_mapcount_val);
+
+ /*
+ * There are valid corner cases where we might underflow a per-MM
+ * mapcount (some mappings added when no slot was free, some mappings
+ * added once a slot was free), so we always set it to -1 once we go
+ * negative.
+ */
+ if (folio_mm_id(folio, 0) == mm_id) {
+ folio->_mm_id_mapcount[0] -= diff;
+ if (folio->_mm_id_mapcount[0] >= 0)
+ goto out;
+ folio->_mm_id_mapcount[0] = -1;
+ folio_set_mm_id(folio, 0, MM_ID_DUMMY);
+ } else if (folio_mm_id(folio, 1) == mm_id) {
+ folio->_mm_id_mapcount[1] -= diff;
+ if (folio->_mm_id_mapcount[1] >= 0)
+ goto out;
+ folio->_mm_id_mapcount[1] = -1;
+ folio_set_mm_id(folio, 1, MM_ID_DUMMY);
+ }
+
+ /*
+ * If one MM slot owns all mappings, the folio is mapped exclusively.
+ * Note that if the folio is now unmapped (new_mapcount_val == -1), both
+ * slots must be free (mapcount == -1), and we'll also mark it as
+ * exclusive.
+ */
+ if (folio->_mm_id_mapcount[0] == new_mapcount_val ||
+ folio->_mm_id_mapcount[1] == new_mapcount_val)
+ folio->_mm_ids &= ~FOLIO_MM_IDS_SHARED_BIT;
+out:
+ folio_unlock_large_mapcount(folio);
+}
+#else /* !CONFIG_MM_ID */
+/*
+ * See __folio_rmap_sanity_checks(), we might map large folios even without
+ * CONFIG_TRANSPARENT_HUGEPAGE. We'll keep that working for now.
+ */
static inline void folio_set_large_mapcount(struct folio *folio, int mapcount,
struct vm_area_struct *vma)
{
@@ -191,6 +355,7 @@ static inline void folio_sub_large_mapcount(struct folio *folio,
{
atomic_sub(diff, &folio->_large_mapcount);
}
+#endif /* CONFIG_MM_ID */
#define folio_inc_large_mapcount(folio, vma) \
folio_add_large_mapcount(folio, 1, vma)
generated by cgit v1.2.3 (git 2.39.0) at 2026-02-14 06:07:54 +0300