[PATCH 4/4] mm: move lesser used vma_area_struct members into the last cacheline

Suren Baghdasaryan
2024-11-11T20:55:19Z

Move several vma_area_struct members which are rarely or never used
during page fault handling into the last cacheline to better pack
vm_area_struct. As a result vm_area_struct will fit into 3 cachelines
as opposed to 4 cachelines before this change. New vm_area_struct layout:

struct vm_area_struct {
union {
struct {
long unsigned int vm_start; /* 0 8 */
long unsigned int vm_end; /* 8 8 */
}; /* 0 16 */
struct callback_head vm_rcu ; /* 0 16 */
} __attribute__((__aligned__(8))); /* 0 16 */
struct mm_struct * vm_mm; /* 16 8 */
pgprot_t vm_page_prot; /* 24 8 */
union {
const vm_flags_t vm_flags; /* 32 8 */
vm_flags_t __vm_flags; /* 32 8 */
}; /* 32 8 */
bool detached; /* 40 1 */

/* XXX 3 bytes hole, try to pack */

unsigned int vm_lock_seq; /* 44 4 */
struct list_head anon_vma_chain; /* 48 16 */
/* --- cacheline 1 boundary (64 bytes) --- */
struct anon_vma * anon_vma; /* 64 8 */
const struct vm_operations_struct * vm_ops; /* 72 8 */
long unsigned int vm_pgoff; /* 80 8 */
struct file * vm_file; /* 88 8 */
void * vm_private_data; /* 96 8 */
atomic_long_t swap_readahead_info; /* 104 8 */
struct mempolicy * vm_policy; /* 112 8 */

/* XXX 8 bytes hole, try to pack */

/* --- cacheline 2 boundary (128 bytes) --- */
struct vma_lock vm_lock (__aligned__(64)); /* 128 4 */

/* XXX 4 bytes hole, try to pack */

struct {
struct rb_node rb (__aligned__(8)); /* 136 24 */
long unsigned int rb_subtree_last; /* 160 8 */
} __attribute__((__aligned__(8))) shared; /* 136 32 */
struct vm_userfaultfd_ctx vm_userfaultfd_ctx; /* 168 0 */

/* size: 192, cachelines: 3, members: 17 */
/* sum members: 153, holes: 3, sum holes: 15 */
/* padding: 24 */
/* forced alignments: 3, forced holes: 2, sum forced holes: 12 */
} __attribute__((__aligned__(64)));

Memory consumption per 1000 VMAs becomes 48 pages:

slabinfo after vm_area_struct changes:
<name> ... <objsize> <objperslab> <pagesperslab> : ...
vm_area_struct ... 192 42 2 : ...

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/mm_types.h | 37 ++++++++++++++++++-------------------
1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 789bccc05520..c3755b680911 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -733,16 +733,6 @@ struct vm_area_struct {
unsigned int vm_lock_seq;
#endif

- /*
- * For areas with an address space and backing store,
- * linkage into the address_space->i_mmap interval tree.
- *
- */
- struct {
- struct rb_node rb;
- unsigned long rb_subtree_last;
- } shared;
-
/*
* A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
* list, after a COW of one of the file pages. A MAP_SHARED vma
@@ -762,14 +752,6 @@ struct vm_area_struct {
struct file * vm_file; /* File we map to (can be NULL). */
void * vm_private_data; /* was vm_pte (shared mem) */

-#ifdef CONFIG_ANON_VMA_NAME
- /*
- * For private and shared anonymous mappings, a pointer to a null
- * terminated string containing the name given to the vma, or NULL if
- * unnamed. Serialized by mmap_lock. Use anon_vma_name to access.
- */
- struct anon_vma_name *anon_name;
-#endif
#ifdef CONFIG_SWAP
atomic_long_t swap_readahead_info;
#endif
@@ -782,11 +764,28 @@ struct vm_area_struct {
#ifdef CONFIG_NUMA_BALANCING
struct vma_numab_state *numab_state; /* NUMA Balancing state */
#endif
- struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
#ifdef CONFIG_PER_VMA_LOCK
/* Unstable RCU readers are allowed to read this. */
struct vma_lock vm_lock ____cacheline_aligned_in_smp;
#endif
+ /*
+ * For areas with an address space and backing store,
+ * linkage into the address_space->i_mmap interval tree.
+ *
+ */
+ struct {
+ struct rb_node rb;
+ unsigned long rb_subtree_last;
+ } shared;
+#ifdef CONFIG_ANON_VMA_NAME
+ /*
+ * For private and shared anonymous mappings, a pointer to a null
+ * terminated string containing the name given to the vma, or NULL if
+ * unnamed. Serialized by mmap_lock. Use anon_vma_name to access.
+ */
+ struct anon_vma_name *anon_name;
+#endif
+ struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
} __randomize_layout;

#ifdef CONFIG_NUMA
--
2.47.0.277.g8800431eea-goog