[PATCH 3/4] add ksm kernel shared memory driver.

From: Izik Eidus
Date: Sun Nov 16 2008 - 21:22:51 EST

Ksm is driver that allow merging identical pages between one or more
applications in way unvisible to the application that use it.
Pages that are merged are marked as readonly and are COWed when any
application try to change them.

Ksm is used for cases where using fork() is not suitable,
one of this cases is where the pages of the application keep changing
dynamicly and the application cannot know in advance what pages are
going to be identical.

Ksm works by walking over the memory pages of the applications it
scan in order to find identical pages.
It uses a hash table to find in effective way the identical pages.

When ksm finds two identical pages, it marks them as readonly and merges
them into single one page,
after the pages are marked as readonly and merged into one page, linux
will treat this pages as normal copy_on_write pages and will fork them
when write access will happen to them.

Ksm scan just memory areas that were registred to be scanned by it.

Ksm api:

KSM_GET_API_VERSION:
Give the userspace the api version of the module.

KSM_CREATE_SHARED_MEMORY_AREA:
Create shared memory reagion fd, that latter allow the user to register
the memory region to scan by using:
KSM_REGISTER_MEMORY_REGION and KSM_REMOVE_MEMORY_REGION

KSM_CREATE_SCAN:
Create the ksm scanner fd, that latter allow the user to create
userspace context scanner that is running by the KSM_SCAN ioctl.

KSM_START_STOP_KTHREAD:
Return information about the kernel thread, the inforamtion is returned
using the ksm_kthread_info structure:
ksm_kthread_info:
__u32 sleep:
number of microsecoends to sleep between each iteration of
scanning.

__u32 pages_to_scan:
number of pages to scan for each iteration of scanning.

__u32 max_pages_to_merge:
maximum number of pages to merge in each iteration of scanning
(so even if there are still more pages to scan, we stop this
iteration)

__u32 flags:
flags to control ksmd (right now just ksm_control_flags_run
available)

KSM_REGISTER_MEMORY_REGION:
Register userspace virtual address range to be scanned by ksm.
This ioctl is using the ksm_memory_region structure:
ksm_memory_region:
__u32 npages;
number of pages to share inside this memory region.
__u32 pad;
__u64 addr:
the begining of the virtual address of this region.

KSM_REMOVE_MEMORY_REGION:
Remove memory region from ksm.

KSM_SCAN:
Tell to ksm start to scan number of pages,
this ioctl is using the ksm_user_scan structure:
ksm_user_scan:
__u32 pages_to_scan:
number of pages to scan in this iteration of scanning.
__u32 max_pages_to_merge:
maximum number of pages to merge in this iteration of scanning
(so even if there are still more pages to scan,
we stop this iteration)
__u32 flags:
flags to control ksm scaning (right now just
ksm_control_flags_run
available)

Signed-off-by: Izik Eidus <ieidus@xxxxxxxxxx>
---
drivers/Kconfig | 6 +
include/linux/ksm.h | 79 +++
include/linux/miscdevice.h | 1 +
mm/Kconfig | 3 +
mm/Makefile | 1 +
mm/ksm.c | 1289 ++++++++++++++++++++++++++++++++++++++++++++
6 files changed, 1379 insertions(+), 0 deletions(-)
create mode 100644 include/linux/ksm.h
create mode 100644 mm/ksm.c

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 2f557f5..a55d49f 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -107,4 +107,10 @@ source "drivers/uio/Kconfig"
source "drivers/xen/Kconfig"

source "drivers/staging/Kconfig"
+
+config PAGE_SHARING
+ bool "KSM page sharing driver support"
+ depends on CRYPTO_SHA1
+ help
+ ksm is a driver for merging identical pages between applciations
endmenu
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
new file mode 100644
index 0000000..60198f5
--- /dev/null
+++ b/include/linux/ksm.h
@@ -0,0 +1,79 @@
+#ifndef __LINUX_KSM_H
+#define __LINUX_KSM_H
+
+/*
+ * Userspace interface for /dev/ksm - kvm shared memory
+ */
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define KSM_API_VERSION 1
+
+#define ksm_control_flags_run 1
+
+/* for KSM_REGISTER_MEMORY_REGION */
+struct ksm_memory_region {
+ __u32 npages; /* number of pages to share */
+ __u32 pad;
+ __u64 addr; /* the begining of the virtual address */
+};
+
+struct ksm_user_scan {
+ __u32 pages_to_scan;
+ __u32 max_pages_to_merge;
+ __u32 flags; /* control flags */
+};
+
+struct ksm_kthread_info {
+ __u32 sleep; /* number of microsecoends to sleep */
+ __u32 pages_to_scan; /* number of pages to scan */
+ __u32 max_pages_to_merge; /* maximum number of pages to merge */
+ __u32 flags; /* control flags */
+};
+
+#define KSMIO 0xAB
+
+/* ioctls for /dev/ksm */
+
+#define KSM_GET_API_VERSION _IO(KSMIO, 0x00)
+/*
+ * KSM_CREATE_SHARED_MEMORY_AREA - create the shared memory reagion fd
+ */
+#define KSM_CREATE_SHARED_MEMORY_AREA _IO(KSMIO, 0x01) /* return SMA fd */
+/*
+ * KSM_CREATE_SCAN - create the scanner fd
+ */
+#define KSM_CREATE_SCAN _IO(KSMIO, 0x02) /* return SCAN fd */
+/*
+ * KSM_START_STOP_KTHREAD - control the kernel thread scanning speed
+ * (can stop the kernel thread from working by setting running = 0)
+ */
+#define KSM_START_STOP_KTHREAD _IOW(KSMIO, 0x03,\
+ struct ksm_kthread_info)
+/*
+ * KSM_GET_INFO_KTHREAD - return information about the kernel thread
+ * scanning speed.
+ */
+#define KSM_GET_INFO_KTHREAD _IOW(KSMIO, 0x04,\
+ struct ksm_kthread_info)
+
+
+/* ioctls for SMA fds */
+
+/*
+ * KSM_REGISTER_MEMORY_REGION - register virtual address memory area to be
+ * scanned by kvm.
+ */
+#define KSM_REGISTER_MEMORY_REGION _IOW(KSMIO, 0x20,\
+ struct ksm_memory_region)
+/*
+ * KSM_REMOVE_MEMORY_REGION - remove virtual address memory area from ksm.
+ */
+#define KSM_REMOVE_MEMORY_REGION _IO(KSMIO, 0x21)
+
+/* ioctls for SCAN fds */
+#define KSM_SCAN _IOW(KSMIO, 0x40,\
+ struct ksm_user_scan)
+
+#endif
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index 26433ec..adc2435 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -30,6 +30,7 @@
#define TUN_MINOR 200
#define HPET_MINOR 228
#define KVM_MINOR 232
+#define KSM_MINOR 233

struct device;

diff --git a/mm/Kconfig b/mm/Kconfig
index 5b5790f..8879485 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -222,3 +222,6 @@ config UNEVICTABLE_LRU

config MMU_NOTIFIER
bool
+
+config PAGE_SHARING
+ bool
diff --git a/mm/Makefile b/mm/Makefile
index c06b45a..7f740c5 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -26,6 +26,7 @@ obj-$(CONFIG_TMPFS_POSIX_ACL) += shmem_acl.o
obj-$(CONFIG_TINY_SHMEM) += tiny-shmem.o
obj-$(CONFIG_SLOB) += slob.o
obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
+obj-$(CONFIG_PAGE_SHARING) += ksm.o
obj-$(CONFIG_SLAB) += slab.o
obj-$(CONFIG_SLUB) += slub.o
obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
diff --git a/mm/ksm.c b/mm/ksm.c
new file mode 100644
index 0000000..707be52
--- /dev/null
+++ b/mm/ksm.c
@@ -0,0 +1,1289 @@
+/*
+ * Memory merging driver for Linux
+ *
+ * This module enables dynamic sharing of identical pages found in different
+ * memory areas, even if they are not shared by fork()
+ *
+ * Copyright (C) 2008 Red Hat, Inc.
+ * Authors:
+ * Izik Eidus
+ * Andrea Arcangeli
+ * Chris Wright
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/vmalloc.h>
+#include <linux/file.h>
+#include <linux/mman.h>
+#include <linux/sched.h>
+#include <linux/rwsem.h>
+#include <linux/pagemap.h>
+#include <linux/sched.h>
+#include <linux/rmap.h>
+#include <linux/spinlock.h>
+#include <linux/jhash.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/wait.h>
+#include <linux/anon_inodes.h>
+#include <linux/ksm.h>
+#include <linux/crypto.h>
+#include <linux/scatterlist.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <crypto/sha.h>
+
+#include <asm/tlbflush.h>
+
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+static int page_hash_size;
+module_param(page_hash_size, int, 0);
+MODULE_PARM_DESC(page_hash_size, "Hash table size for the pages checksum");
+
+static int rmap_hash_size;
+module_param(rmap_hash_size, int, 0);
+MODULE_PARM_DESC(rmap_hash_size, "Hash table size for the reverse mapping");
+
+static int sha1_hash_size;
+module_param(sha1_hash_size, int, 0);
+MODULE_PARM_DESC(sha1_hash_size, "Hash table size for the sha1 caching");
+
+/*
+ * ksm_mem_slot - hold information for an userspace scanning range
+ * (the scanning for this region will be from addr untill addr +
+ * npages * PAGE_SIZE inside mm)
+ */
+struct ksm_mem_slot {
+ struct list_head link;
+ struct list_head sma_link;
+ struct mm_struct *mm;
+ unsigned long addr; /* the begining of the virtual address */
+ int npages; /* number of pages to share */
+};
+
+/*
+ * ksm_sma - shared memory area, each process have its own sma that contain the
+ * information about the slots that it own
+ */
+struct ksm_sma {
+ struct list_head sma_slots;
+};
+
+/**
+ * struct ksm_scan - cursor for scanning
+ * @slot_index: the current slot we are scanning
+ * @page_index: the page inside the sma that is currently being scanned
+ *
+ * ksm uses it to know what are the next pages it need to scan
+ */
+struct ksm_scan {
+ struct ksm_mem_slot *slot_index;
+ unsigned long page_index;
+};
+
+/*
+ * Few notes about ksm scanning progress (make it easier to understand the
+ * structures below):
+ *
+ * In order to reduce excessive scanning, pages are sorted into the hash
+ * table, page_hash. After a page is inserted into the hash table, its
+ * contents may have changed. In this case, ksm must remove the page from
+ * the hash table and potentially rehash it. Ksm uses a reverse mapping,
+ * rmap_hash, to efficiently manage this.
+ */
+
+/*
+ * page_hash_item - object of the page_hash hash table
+ * (it is holding the mm_struct and address of the page)
+ */
+struct page_hash_item {
+ struct hlist_node link;
+ struct mm_struct *mm;
+ unsigned long addr;
+};
+
+/*
+ * rmap_item - object of the rmap_hash hash table
+ * (it is holding the previous hash value (oldindex),
+ * and pointer into the page_hash_item)
+ */
+struct rmap_item {
+ struct hlist_node link;
+ struct page_hash_item *page_hash_item;
+ unsigned long oldindex; /* old hash value */
+};
+
+/*
+ * Few notes about the sha1 caching:
+ *
+ * After ksm find two identical pages it computes the first 128 bytes sha1
+ * value of this pages and check if they are identical,
+ * to speedup this operation ksm use caching for the sha1 values.
+ * The caching take into account three fundamental assumptions into account:
+ * 1) PageKSM are only allocated by KSM (we are safe even if the user give to us
+ * virtual address of file backed memory, beacuse cmp_and_merge_page will be
+ * called just for anonymous pages)
+ * 2) PageKSM are always write protect
+ * 3) PageKSM cant be free without we will notice it before check the sha1 val
+ * and it cannot be swapped away.
+ */
+
+struct sha1_item {
+ unsigned char sha1val[SHA1_DIGEST_SIZE];
+ unsigned long pfn;
+};
+
+/*
+ * slots is linked list that hold all the memory regions that were registred
+ * to be scanned.
+ */
+static LIST_HEAD(slots);
+static DECLARE_RWSEM(slots_lock);
+
+static DEFINE_MUTEX(sha1_lock);
+
+static int npages_hash;
+/* page_hash hash table */
+static struct hlist_head *page_hash_items;
+static int nrmaps_hash;
+/* rmap_hash hash table */
+static struct hlist_head *rmap_hash;
+static int nsha1s_hash;
+static struct sha1_item *sha1_hash;
+
+static struct kmem_cache *page_hash_item_cache;
+static struct kmem_cache *rmap_item_cache;
+
+static int kthread_sleep; /* sleep time of the kernel thread */
+static int kthread_pages_to_scan; /* npages to scan for the kernel thread */
+static int kthread_max_npages; /* max pages to merge for the kernel thread */
+static struct ksm_scan kthread_ksm_scan;
+static int ksmd_flags;
+static struct task_struct *kthread;
+static DECLARE_WAIT_QUEUE_HEAD(kthread_wait);
+static DECLARE_RWSEM(kthread_lock);
+static struct crypto_hash *tfm;
+static unsigned char hmac_key[SHA1_DIGEST_SIZE];
+static DEFINE_MUTEX(tfm_mutex);
+
+/*
+ * ksm scanners can run parallel, this lock protect the page_hash and rmap_hash
+ * hash tables.
+ */
+static DEFINE_SPINLOCK(hash_lock);
+
+static int ksm_tfm_init(void)
+{
+ struct crypto_hash *hash;
+ int rc = 0;
+
+ mutex_lock(&tfm_mutex);
+ if (tfm)
+ goto out;
+
+ /* Must be called from user context before starting any scanning */
+ hash = crypto_alloc_hash("hmac(sha1)", 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR(hash)) {
+ rc = PTR_ERR(hash);
+ goto out;
+ }
+
+ get_random_bytes(hmac_key, sizeof(hmac_key));
+
+ rc = crypto_hash_setkey(hash, hmac_key, SHA1_DIGEST_SIZE);
+ if (rc) {
+ crypto_free_hash(hash);
+ goto out;
+ }
+ tfm = hash;
+out:
+ mutex_unlock(&tfm_mutex);
+ return rc;
+}
+
+static int ksm_slab_init(void)
+{
+ int ret = -ENOMEM;
+
+ page_hash_item_cache = KMEM_CACHE(page_hash_item, 0);
+ if (!page_hash_item_cache)
+ goto out;
+
+ rmap_item_cache = KMEM_CACHE(rmap_item, 0);
+ if (!rmap_item_cache)
+ goto out_free;
+ return 0;
+
+out_free:
+ kmem_cache_destroy(page_hash_item_cache);
+out:
+ return ret;
+}
+
+static void ksm_slab_free(void)
+{
+ kmem_cache_destroy(rmap_item_cache);
+ kmem_cache_destroy(page_hash_item_cache);
+}
+
+static inline struct page_hash_item *alloc_page_hash_item(void)
+{
+
+ return kmem_cache_zalloc(page_hash_item_cache, GFP_KERNEL);
+}
+
+static inline void free_page_hash_item(struct page_hash_item *page_hash_item)
+{
+ kmem_cache_free(page_hash_item_cache, page_hash_item);
+}
+
+static inline struct rmap_item *alloc_rmap_item(void)
+{
+ return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+}
+
+static inline void free_rmap_item(struct rmap_item *rmap_item)
+{
+ kmem_cache_free(rmap_item_cache, rmap_item);
+}
+
+/*
+ * PageKsm - this type of pages are the write protected pages that ksm map
+ * into multiple vmas (this is the "shared page")
+ * this page was allocated using alloc_page(), every pte that pointing to it
+ * is always write protected (therefore its data content cant ever be changed)
+ * and this page cant be swapped.
+ */
+static inline int PageKsm(struct page *page)
+{
+ return !PageAnon(page);
+}
+
+static int page_hash_init(void)
+{
+ if (!page_hash_size) {
+ page_hash_size = nr_free_buffer_pages();
+ page_hash_size /= 10;
+ }
+ npages_hash = page_hash_size;
+ page_hash_items = vmalloc(npages_hash * sizeof(struct page_hash_item));
+ if (!page_hash_items)
+ return -ENOMEM;
+
+ memset(page_hash_items, 0, npages_hash * sizeof(struct page_hash_item));
+ return 0;
+}
+
+static void page_hash_free(void)
+{
+ int i;
+ struct hlist_head *bucket;
+ struct hlist_node *node, *n;
+ struct page_hash_item *page_hash_item;
+
+ for (i = 0; i < npages_hash; ++i) {
+ bucket = &page_hash_items[i];
+ hlist_for_each_entry_safe(page_hash_item, node, n, bucket, link) {
+ hlist_del(&page_hash_item->link);
+ free_page_hash_item(page_hash_item);
+ }
+ }
+ vfree(page_hash_items);
+}
+
+static int rmap_hash_init(void)
+{
+ if (!rmap_hash_size) {
+ rmap_hash_size = nr_free_buffer_pages();
+ rmap_hash_size /= 10;
+ }
+ nrmaps_hash = rmap_hash_size;
+ rmap_hash = vmalloc(nrmaps_hash * sizeof(struct hlist_head));
+ if (!rmap_hash)
+ return -ENOMEM;
+ memset(rmap_hash, 0, nrmaps_hash * sizeof(struct hlist_head));
+ return 0;
+}
+
+static void rmap_hash_free(void)
+{
+ int i;
+ struct hlist_head *bucket;
+ struct hlist_node *node, *n;
+ struct rmap_item *rmap_item;
+
+ for (i = 0; i < nrmaps_hash; ++i) {
+ bucket = &rmap_hash[i];
+ hlist_for_each_entry_safe(rmap_item, node, n, bucket, link) {
+ hlist_del(&rmap_item->link);
+ free_rmap_item(rmap_item);
+ }
+ }
+ vfree(rmap_hash);
+}
+
+static int sha1_hash_init(void)
+{
+ if (!sha1_hash_size) {
+ sha1_hash_size = nr_free_buffer_pages();
+ sha1_hash_size /= 32;
+ }
+ nsha1s_hash = sha1_hash_size;
+ sha1_hash = vmalloc(nsha1s_hash * sizeof(struct sha1_item));
+ if (!sha1_hash)
+ return -ENOMEM;
+ memset(sha1_hash, 0, nsha1s_hash * sizeof(struct sha1_item));
+ return 0;
+}
+
+static void sha1_hash_free(void)
+{
+ vfree(sha1_hash);
+}
+
+static inline u32 calc_hash_index(struct page *page)
+{
+ u32 hash;
+ void *addr = kmap_atomic(page, KM_USER0);
+ hash = jhash(addr, PAGE_SIZE, 17);
+ kunmap_atomic(addr, KM_USER0);
+ return hash % npages_hash;
+}
+
+static void remove_page_from_hash(struct mm_struct *mm, unsigned long addr)
+{
+ struct rmap_item *rmap_item;
+ struct hlist_head *bucket;
+ struct hlist_node *node, *n;
+
+ bucket = &rmap_hash[addr % nrmaps_hash];
+ hlist_for_each_entry_safe(rmap_item, node, n, bucket, link) {
+ if (mm == rmap_item->page_hash_item->mm &&
+ rmap_item->page_hash_item->addr == addr) {
+ hlist_del(&rmap_item->page_hash_item->link);
+ free_page_hash_item(rmap_item->page_hash_item);
+ hlist_del(&rmap_item->link);
+ free_rmap_item(rmap_item);
+ return;
+ }
+ }
+}
+
+static int ksm_sma_ioctl_register_memory_region(struct ksm_sma *ksm_sma,
+ struct ksm_memory_region *mem)
+{
+ struct ksm_mem_slot *slot;
+ int ret = -EPERM;
+
+ slot = kzalloc(sizeof(struct ksm_mem_slot), GFP_KERNEL);
+ if (!slot) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ slot->mm = get_task_mm(current);
+ if (!slot->mm)
+ goto out_free;
+ slot->addr = mem->addr;
+ slot->npages = mem->npages;
+
+ down_write(&slots_lock);
+
+ list_add_tail(&slot->link, &slots);
+ list_add_tail(&slot->sma_link, &ksm_sma->sma_slots);
+
+ up_write(&slots_lock);
+ return 0;
+
+out_free:
+ kfree(slot);
+out:
+ return ret;
+}
+
+static void remove_mm_from_hash(struct mm_struct *mm)
+{
+ struct ksm_mem_slot *slot;
+ int pages_count;
+
+ list_for_each_entry(slot, &slots, link)
+ if (slot->mm == mm)
+ break;
+ BUG_ON(!slot);
+
+ spin_lock(&hash_lock);
+ for (pages_count = 0; pages_count < slot->npages; ++pages_count)
+ remove_page_from_hash(mm, slot->addr + pages_count * PAGE_SIZE);
+ spin_unlock(&hash_lock);
+ list_del(&slot->link);
+}
+
+static int ksm_sma_ioctl_remove_memory_region(struct ksm_sma *ksm_sma)
+{
+ struct ksm_mem_slot *slot, *node;
+
+ down_write(&slots_lock);
+ list_for_each_entry_safe(slot, node, &ksm_sma->sma_slots, sma_link) {
+ remove_mm_from_hash(slot->mm);
+ mmput(slot->mm);
+ list_del(&slot->sma_link);
+ kfree(slot);
+ }
+ up_write(&slots_lock);
+ return 0;
+}
+
+static int ksm_sma_release(struct inode *inode, struct file *filp)
+{
+ struct ksm_sma *ksm_sma = filp->private_data;
+ int r;
+
+ r = ksm_sma_ioctl_remove_memory_region(ksm_sma);
+ kfree(ksm_sma);
+ return r;
+}
+
+static long ksm_sma_ioctl(struct file *filp,
+ unsigned int ioctl, unsigned long arg)
+{
+ struct ksm_sma *sma = filp->private_data;
+ void __user *argp = (void __user *)arg;
+ int r = EINVAL;
+
+ switch (ioctl) {
+ case KSM_REGISTER_MEMORY_REGION: {
+ struct ksm_memory_region ksm_memory_region;
+
+ r = -EFAULT;
+ if (copy_from_user(&ksm_memory_region, argp,
+ sizeof(ksm_memory_region)))
+ goto out;
+ r = ksm_sma_ioctl_register_memory_region(sma,
+ &ksm_memory_region);
+ break;
+ }
+ case KSM_REMOVE_MEMORY_REGION:
+ r = ksm_sma_ioctl_remove_memory_region(sma);
+ break;
+ }
+
+out:
+ return r;
+}
+
+static int insert_page_to_hash(struct ksm_scan *ksm_scan,
+ unsigned long hash_index,
+ struct page_hash_item *page_hash_item,
+ struct rmap_item *rmap_item)
+{
+ struct ksm_mem_slot *slot;
+ struct hlist_head *bucket;
+
+ slot = ksm_scan->slot_index;
+ page_hash_item->addr = slot->addr + ksm_scan->page_index * PAGE_SIZE;
+ page_hash_item->mm = slot->mm;
+ bucket = &page_hash_items[hash_index];
+ hlist_add_head(&page_hash_item->link, bucket);
+
+ rmap_item->page_hash_item = page_hash_item;
+ rmap_item->oldindex = hash_index;
+ bucket = &rmap_hash[page_hash_item->addr % nrmaps_hash];
+ hlist_add_head(&rmap_item->link, bucket);
+ return 0;
+}
+
+/*
+ * update_hash - check the previoes hash value of the page and if it was changed
+ * since the last time we compute it it remove it from the hash table.
+ */
+static void update_hash(struct ksm_scan *ksm_scan,
+ unsigned long hash_index)
+{
+ struct rmap_item *rmap_item;
+ struct ksm_mem_slot *slot;
+ struct hlist_head *bucket;
+ struct hlist_node *node, *n;
+ unsigned long addr;
+
+ slot = ksm_scan->slot_index;
+ addr = slot->addr + ksm_scan->page_index * PAGE_SIZE;
+ bucket = &rmap_hash[addr % nrmaps_hash];
+ hlist_for_each_entry_safe(rmap_item, node, n, bucket, link) {
+ if (slot->mm == rmap_item->page_hash_item->mm &&
+ rmap_item->page_hash_item->addr == addr) {
+ if (hash_index != rmap_item->oldindex) {
+ hlist_del(&rmap_item->page_hash_item->link);
+ free_page_hash_item(rmap_item->page_hash_item);
+ hlist_del(&rmap_item->link);
+ free_rmap_item(rmap_item);
+ }
+ return;
+ }
+ }
+}
+
+static unsigned long addr_in_vma(struct vm_area_struct *vma, struct page *page)
+{
+ pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+ unsigned long addr;
+
+ addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+ if (unlikely(addr < vma->vm_start || addr >= vma->vm_end))
+ return -EFAULT;
+ return addr;
+}
+
+static pte_t *get_pte(struct mm_struct *mm, unsigned long addr)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *ptep = NULL;
+
+ pgd = pgd_offset(mm, addr);
+ if (!pgd_present(*pgd))
+ goto out;
+
+ pud = pud_offset(pgd, addr);
+ if (!pud_present(*pud))
+ goto out;
+
+ pmd = pmd_offset(pud, addr);
+ if (!pmd_present(*pmd))
+ goto out;
+
+ ptep = pte_offset_map(pmd, addr);
+out:
+ return ptep;
+}
+
+static int is_present_pte(struct mm_struct *mm, unsigned long addr)
+{
+ pte_t *ptep;
+
+ ptep = get_pte(mm, addr);
+ if (!ptep)
+ return 0;
+
+ if (pte_present(*ptep))
+ return 1;
+ return 0;
+}
+
+#define PAGEHASH_LEN 128
+/* hash the page */
+static void page_hash(struct page *page, unsigned char *digest)
+{
+ struct scatterlist sg;
+ struct hash_desc desc;
+
+ sg_init_table(&sg, 1);
+ sg_set_page(&sg, page, PAGEHASH_LEN, 0);
+ desc.tfm = tfm;
+ desc.flags = 0;
+ crypto_hash_digest(&desc, &sg, PAGEHASH_LEN, digest);
+}
+
+/* pages_identical
+ * calculate sha1 hash of each page, compare results,
+ * and return 1 if identical, 0 otherwise.
+ */
+static int pages_identical(struct page *oldpage, struct page *newpage, int new)
+{
+ int r;
+ unsigned char old_digest[SHA1_DIGEST_SIZE];
+ struct sha1_item *sha1_item;
+
+ page_hash(oldpage, old_digest);
+ /*
+ * If new = 1, it is never safe to use the sha1 value that is
+ * inside the cache, the reason is that the page can be released
+ * and then recreated and have diffrent sha1 value.
+ * (swapping as for now is not an issue, because KsmPages cannot be
+ * swapped)
+ */
+ mutex_lock(&sha1_lock);
+ if (new) {
+ sha1_item = &sha1_hash[page_to_pfn(newpage) % nsha1s_hash];
+ page_hash(newpage, sha1_item->sha1val);
+ sha1_item->pfn = page_to_pfn(newpage);
+ } else {
+ sha1_item = &sha1_hash[page_to_pfn(newpage) % nsha1s_hash];
+ if (sha1_item->pfn != page_to_pfn(newpage)) {
+ page_hash(newpage, sha1_item->sha1val);
+ sha1_item->pfn = page_to_pfn(newpage);
+ }
+ }
+ r = !memcmp(old_digest, sha1_item->sha1val, SHA1_DIGEST_SIZE);
+ mutex_unlock(&sha1_lock);
+ if (r) {
+ char *old_addr, *new_addr;
+ old_addr = kmap_atomic(oldpage, KM_USER0);
+ new_addr = kmap_atomic(newpage, KM_USER1);
+ r = !memcmp(old_addr+PAGEHASH_LEN, new_addr+PAGEHASH_LEN,
+ PAGE_SIZE-PAGEHASH_LEN);
+ kunmap_atomic(old_addr, KM_USER0);
+ kunmap_atomic(new_addr, KM_USER1);
+ }
+ return r;
+}
+
+/*
+ * try_to_merge_one_page - take two pages and merge them into one
+ * note:
+ * oldpage should be anon page while newpage should be file mapped page
+ *
+ * this function return 0 if the pages were merged, 1 otherwise.
+ */
+static int try_to_merge_one_page(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ struct page *oldpage,
+ struct page *newpage,
+ pgprot_t newprot,
+ int new)
+{
+ int ret = 1;
+ int odirect_sync;
+ unsigned long page_addr_in_vma;
+ pte_t orig_pte, *orig_ptep;
+
+ get_page(newpage);
+ get_page(oldpage);
+
+ down_read(&mm->mmap_sem);
+
+ page_addr_in_vma = addr_in_vma(vma, oldpage);
+ if (page_addr_in_vma == -EFAULT)
+ goto out_unlock;
+
+ orig_ptep = get_pte(mm, page_addr_in_vma);
+ if (!orig_ptep)
+ goto out_unlock;
+ orig_pte = *orig_ptep;
+ if (!pte_present(orig_pte))
+ goto out_unlock;
+ if (page_to_pfn(oldpage) != pte_pfn(orig_pte))
+ goto out_unlock;
+ /*
+ * we need the page lock to read a stable PageSwapCache in
+ * page_wrprotect()
+ */
+ if (!trylock_page(oldpage))
+ goto out_unlock;
+ /*
+ * page_wrprotect check if the page is swapped or in swap cache,
+ * in the future we might want to run here if_present_pte and then
+ * swap_free
+ */
+ if (!page_wrprotect(oldpage, &odirect_sync, 2)) {
+ unlock_page(oldpage);
+ goto out_unlock;
+ }
+ unlock_page(oldpage);
+ if (!odirect_sync)
+ goto out_unlock;
+
+ orig_pte = pte_wrprotect(orig_pte);
+
+ if (pages_identical(oldpage, newpage, new))
+ ret = replace_page(vma, oldpage, newpage, orig_pte, newprot);
+
+out_unlock:
+ up_read(&mm->mmap_sem);
+ put_page(oldpage);
+ put_page(newpage);
+ return ret;
+}
+
+/*
+ * try_to_merge_two_pages - take two identical pages and prepare them to be
+ * merged into one page.
+ *
+ * this function return 0 if we successfully mapped two identical pages into one
+ * page, 1 otherwise.
+ * (note in case we created KsmPage and mapped one page into it but the second
+ * page was not mapped we consider it as a failure and return 1)
+ */
+static int try_to_merge_two_pages(struct mm_struct *mm1, struct page *page1,
+ struct mm_struct *mm2, struct page *page2,
+ unsigned long addr1, unsigned long addr2)
+{
+ struct vm_area_struct *vma;
+ pgprot_t prot;
+ int ret = 1;
+
+ /*
+ * If page2 isn't shared (it isn't PageKsm) we have to allocate a new
+ * file mapped page and make the two ptes of mm1(page1) and mm2(page2)
+ * point to it. If page2 is shared, we can just make the pte of
+ * mm1(page1) point to page2
+ */
+ if (PageKsm(page2)) {
+ vma = find_vma(mm1, addr1);
+ if (!vma)
+ return ret;
+ prot = vma->vm_page_prot;
+ pgprot_val(prot) &= ~VM_WRITE;
+ ret = try_to_merge_one_page(mm1, vma, page1, page2, prot, 0);
+ } else {
+ struct page *kpage;
+
+ kpage = alloc_page(GFP_HIGHUSER);
+ if (!kpage)
+ return ret;
+ vma = find_vma(mm1, addr1);
+ if (!vma) {
+ put_page(kpage);
+ return ret;
+ }
+ prot = vma->vm_page_prot;
+ pgprot_val(prot) &= ~VM_WRITE;
+
+ copy_user_highpage(kpage, page1, addr1, vma);
+ ret = try_to_merge_one_page(mm1, vma, page1, kpage, prot, 1);
+
+ if (!ret) {
+ vma = find_vma(mm2, addr2);
+ if (!vma) {
+ put_page(kpage);
+ ret = 1;
+ return ret;
+ }
+
+ prot = vma->vm_page_prot;
+ pgprot_val(prot) &= ~VM_WRITE;
+
+ ret = try_to_merge_one_page(mm2, vma, page2, kpage,
+ prot, 0);
+ }
+ put_page(kpage);
+ }
+ return ret;
+}
+
+/*
+ * cmp_and_merge_page - take a page computes its hash value and check if there
+ * is similar hash value to different page,
+ * in case we find that there is similar hash to different page we call to
+ * try_to_merge_two_pages().
+ */
+static int cmp_and_merge_page(struct ksm_scan *ksm_scan, struct page *page)
+{
+ struct hlist_head *bucket;
+ struct hlist_node *node, *n;
+ struct page_hash_item *page_hash_item;
+ struct ksm_mem_slot *slot;
+ unsigned long hash_index;
+ unsigned long addr;
+ int used = 0;
+
+ hash_index = calc_hash_index(page);
+ bucket = &page_hash_items[hash_index];
+
+ slot = ksm_scan->slot_index;
+ addr = slot->addr + ksm_scan->page_index * PAGE_SIZE;
+
+ spin_lock(&hash_lock);
+ /*
+ * update_hash must be called every time because there is a chance
+ * that the data in the page has changed since the page was inserted
+ * into the hash table, by calling to this we are avoiding inserting
+ * the page more than once to our hash table.
+ */
+ update_hash(ksm_scan, hash_index);
+ spin_unlock(&hash_lock);
+
+ hlist_for_each_entry_safe(page_hash_item, node, n, bucket, link) {
+ int npages;
+ struct page *hash_page[1];
+
+ if (slot->mm == page_hash_item->mm && addr == page_hash_item->addr) {
+ used = 1;
+ continue;
+ }
+
+ down_read(&page_hash_item->mm->mmap_sem);
+ /*
+ * If the page is swapped out or in swap cache we don't want to
+ * scan it (it is just for performance).
+ */
+ if (!is_present_pte(page_hash_item->mm, page_hash_item->addr)) {
+ up_read(&page_hash_item->mm->mmap_sem);
+ continue;
+ }
+ npages = get_user_pages(current, page_hash_item->mm,
+ page_hash_item->addr,
+ 1, 0, 0, hash_page, NULL);
+ up_read(&page_hash_item->mm->mmap_sem);
+ if (npages != 1)
+ break;
+
+ /* Recalculate the page's hash index in case it has changed. */
+ if (calc_hash_index(hash_page[0]) == hash_index) {
+ int ret;
+
+ ret = try_to_merge_two_pages(slot->mm, page,
+ page_hash_item->mm,
+ hash_page[0], addr,
+ page_hash_item->addr);
+ if (!ret) {
+ put_page(hash_page[0]);
+ return 1;
+ }
+ }
+ put_page(hash_page[0]);
+ }
+ /* If node is NULL and used=0, the page is not in the hash table. */
+ if (!node && !used) {
+ struct page_hash_item *page_hash_item;
+ struct rmap_item *rmap_item;
+
+ page_hash_item = alloc_page_hash_item();
+ if (!page_hash_item)
+ goto out;
+
+ rmap_item = alloc_rmap_item();
+ if (!rmap_item) {
+ free_page_hash_item(page_hash_item);
+ goto out;
+ }
+
+ spin_lock(&hash_lock);
+ update_hash(ksm_scan, hash_index);
+ insert_page_to_hash(ksm_scan, hash_index, page_hash_item, rmap_item);
+ spin_unlock(&hash_lock);
+ }
+out:
+ return 0;
+}
+
+/* return -EAGAIN - no slots registered, nothing to be done */
+static int scan_get_next_index(struct ksm_scan *ksm_scan, int nscan)
+{
+ struct ksm_mem_slot *slot;
+
+ if (list_empty(&slots))
+ return -EAGAIN;
+
+ slot = ksm_scan->slot_index;
+
+ /* Are there pages left in this slot to scan? */
+ if ((slot->npages - ksm_scan->page_index - nscan) > 0) {
+ ksm_scan->page_index += nscan;
+ return 0;
+ }
+
+ list_for_each_entry_from(slot, &slots, link) {
+ if (slot == ksm_scan->slot_index)
+ continue;
+ ksm_scan->page_index = 0;
+ ksm_scan->slot_index = slot;
+ return 0;
+ }
+
+ /* look like we finished scanning the whole memory, starting again */
+ ksm_scan->page_index = 0;
+ ksm_scan->slot_index = list_first_entry(&slots,
+ struct ksm_mem_slot, link);
+ return 0;
+}
+
+/*
+ * update slot_index - make sure ksm_scan will point to vaild data,
+ * it is possible that by the time we are here the data that ksm_scan was
+ * pointed to was released so we have to call this function every time after
+ * taking the slots_lock
+ */
+static void scan_update_old_index(struct ksm_scan *ksm_scan)
+{
+ struct ksm_mem_slot *slot;
+
+ if (list_empty(&slots))
+ return;
+
+ list_for_each_entry(slot, &slots, link) {
+ if (ksm_scan->slot_index == slot)
+ return;
+ }
+
+ ksm_scan->slot_index = list_first_entry(&slots,
+ struct ksm_mem_slot, link);
+ ksm_scan->page_index = 0;
+}
+
+/**
+ * ksm_scan_start - the ksm scanner main worker function.
+ * @ksm_scan - the scanner.
+ * @scan_npages - number of pages we are want to scan before we return from this
+ * @function.
+ * @max_npages - number of maximum pages we allow to merge before we return from
+ * this function (so even if there are more pages to scan from
+ * scan_npages if we passed the max_npages value we will return
+ * from this function)
+ *
+ * (this function can be called from the kernel thread scanner, or from
+ * userspace ioctl context scanner)
+ *
+ * The function return -EAGAIN in case there are not slots to scan.
+ */
+static int ksm_scan_start(struct ksm_scan *ksm_scan, int scan_npages,
+ int max_npages)
+{
+ struct ksm_mem_slot *slot;
+ struct page *page[1];
+ int val;
+ int ret = 0;
+
+ down_read(&slots_lock);
+
+ scan_update_old_index(ksm_scan);
+
+ while (scan_npages > 0 && max_npages > 0) {
+ ret = scan_get_next_index(ksm_scan, 1);
+ if (ret)
+ goto out;
+
+ slot = ksm_scan->slot_index;
+ down_read(&slot->mm->mmap_sem);
+ /*
+ * If the page is swapped out or in swap cache, we don't want to
+ * scan it (it is just for performance).
+ */
+ if (is_present_pte(slot->mm, slot->addr +
+ ksm_scan->page_index * PAGE_SIZE)) {
+ val = get_user_pages(current, slot->mm, slot->addr +
+ ksm_scan->page_index * PAGE_SIZE ,
+ 1, 0, 0, page, NULL);
+ up_read(&slot->mm->mmap_sem);
+ if (val == 1) {
+ if (!PageKsm(page[0]))
+ max_npages -=
+ cmp_and_merge_page(ksm_scan, page[0]);
+ put_page(page[0]);
+ }
+ } else
+ up_read(&slot->mm->mmap_sem);
+ scan_npages--;
+ }
+
+ scan_get_next_index(ksm_scan, 1);
+out:
+ up_read(&slots_lock);
+ return ret;
+}
+
+static int ksm_scan_ioctl_start(struct ksm_scan *ksm_scan,
+ struct ksm_user_scan *scan)
+{
+ if (!(scan->flags & ksm_control_flags_run))
+ return 0;
+
+ return ksm_scan_start(ksm_scan, scan->pages_to_scan,
+ scan->max_pages_to_merge);
+}
+
+static int ksm_scan_release(struct inode *inode, struct file *filp)
+{
+ struct ksm_scan *ksm_scan = filp->private_data;
+
+ kfree(ksm_scan);
+ return 0;
+}
+
+static long ksm_scan_ioctl(struct file *filp,
+ unsigned int ioctl, unsigned long arg)
+{
+ struct ksm_scan *ksm_scan = filp->private_data;
+ void __user *argp = (void __user *)arg;
+ int r = EINVAL;
+
+ switch (ioctl) {
+ case KSM_SCAN: {
+ struct ksm_user_scan scan;
+
+ r = -EFAULT;
+ if (copy_from_user(&scan, argp,
+ sizeof(struct ksm_user_scan)))
+ break;
+
+ r = ksm_scan_ioctl_start(ksm_scan, &scan);
+ }
+ }
+ return r;
+}
+
+static struct file_operations ksm_sma_fops = {
+ .release = ksm_sma_release,
+ .unlocked_ioctl = ksm_sma_ioctl,
+ .compat_ioctl = ksm_sma_ioctl,
+};
+
+static int ksm_dev_ioctl_create_shared_memory_area(void)
+{
+ int fd = -1;
+ struct ksm_sma *ksm_sma;
+
+ ksm_sma = kmalloc(sizeof(struct ksm_sma), GFP_KERNEL);
+ if (!ksm_sma)
+ goto out;
+
+ INIT_LIST_HEAD(&ksm_sma->sma_slots);
+
+ fd = anon_inode_getfd("ksm-sma", &ksm_sma_fops, ksm_sma, 0);
+ if (fd < 0)
+ goto out_free;
+
+ return fd;
+out_free:
+ kfree(ksm_sma);
+out:
+ return fd;
+}
+
+static struct file_operations ksm_scan_fops = {
+ .release = ksm_scan_release,
+ .unlocked_ioctl = ksm_scan_ioctl,
+ .compat_ioctl = ksm_scan_ioctl,
+};
+
+static struct ksm_scan *ksm_scan_create(void)
+{
+ return kzalloc(sizeof(struct ksm_scan), GFP_KERNEL);
+}
+
+static int ksm_dev_ioctl_create_scan(void)
+{
+ int fd;
+ struct ksm_scan *ksm_scan;
+
+ if (!tfm) {
+ fd = ksm_tfm_init();
+ if (fd)
+ goto out;
+ }
+
+ fd = -ENOMEM;
+ ksm_scan = ksm_scan_create();
+ if (!ksm_scan)
+ goto out;
+
+ fd = anon_inode_getfd("ksm-scan", &ksm_scan_fops, ksm_scan, 0);
+ if (fd < 0)
+ goto out_free;
+ return fd;
+
+out_free:
+ kfree(ksm_scan);
+out:
+ return fd;
+}
+
+/*
+ * ksm_dev_ioctl_start_stop_kthread - control the kernel thread scanning running
+ * speed.
+ * This function allow us to control on the time the kernel thread will sleep
+ * how many pages it will scan between sleep and sleep, and how many pages it
+ * will maximum merge between sleep and sleep.
+ */
+static int ksm_dev_ioctl_start_stop_kthread(struct ksm_kthread_info *info)
+{
+ int rc = 0;
+
+ /* Make sure crypto tfm is initialized before starting scanning */
+ if (info->flags & ksm_control_flags_run && !tfm) {
+ rc = ksm_tfm_init();
+ if (rc)
+ goto out;
+ }
+
+ down_write(&kthread_lock);
+
+ if (info->flags & ksm_control_flags_run) {
+ if (!info->pages_to_scan || !info->max_pages_to_merge) {
+ rc = EPERM;
+ up_write(&kthread_lock);
+ goto out;
+ }
+ }
+
+ kthread_sleep = info->sleep;
+ kthread_pages_to_scan = info->pages_to_scan;
+ kthread_max_npages = info->max_pages_to_merge;
+ ksmd_flags = info->flags;
+
+ up_write(&kthread_lock);
+
+ if (ksmd_flags & ksm_control_flags_run)
+ wake_up_interruptible(&kthread_wait);
+
+out:
+ return rc;
+}
+
+/*
+ * ksm_dev_ioctl_get_info_kthread - write into info the scanning information
+ * of the ksm kernel thread
+ */
+static void ksm_dev_ioctl_get_info_kthread(struct ksm_kthread_info *info)
+{
+ down_read(&kthread_lock);
+
+ info->sleep = kthread_sleep;
+ info->pages_to_scan = kthread_pages_to_scan;
+ info->max_pages_to_merge = kthread_max_npages;
+ info->flags = ksmd_flags;
+
+ up_read(&kthread_lock);
+}
+
+static long ksm_dev_ioctl(struct file *filp,
+ unsigned int ioctl, unsigned long arg)
+{
+ void __user *argp = (void __user *)arg;
+ long r = -EINVAL;
+
+ switch (ioctl) {
+ case KSM_GET_API_VERSION:
+ r = KSM_API_VERSION;
+ break;
+ case KSM_CREATE_SHARED_MEMORY_AREA:
+ r = ksm_dev_ioctl_create_shared_memory_area();
+ break;
+ case KSM_CREATE_SCAN:
+ r = ksm_dev_ioctl_create_scan();
+ break;
+ case KSM_START_STOP_KTHREAD: {
+ struct ksm_kthread_info info;
+
+ r = -EFAULT;
+ if (copy_from_user(&info, argp,
+ sizeof(struct ksm_kthread_info)))
+ break;
+
+ r = ksm_dev_ioctl_start_stop_kthread(&info);
+ break;
+ }
+ case KSM_GET_INFO_KTHREAD: {
+ struct ksm_kthread_info info;
+
+ ksm_dev_ioctl_get_info_kthread(&info);
+ r = -EFAULT;
+ if (copy_to_user(argp, &info,
+ sizeof(struct ksm_kthread_info)))
+ break;
+ r = 0;
+ break;
+ }
+ default:
+ break;
+ }
+ return r;
+}
+
+static struct file_operations ksm_chardev_ops = {
+ .unlocked_ioctl = ksm_dev_ioctl,
+ .compat_ioctl = ksm_dev_ioctl,
+ .owner = THIS_MODULE,
+};
+
+static struct miscdevice ksm_dev = {
+ KSM_MINOR,
+ "ksm",
+ &ksm_chardev_ops,
+};
+
+int kthread_ksm_scan_thread(void *nothing)
+{
+ while (!kthread_should_stop()) {
+ if (ksmd_flags & ksm_control_flags_run) {
+ down_read(&kthread_lock);
+ ksm_scan_start(&kthread_ksm_scan,
+ kthread_pages_to_scan,
+ kthread_max_npages);
+ up_read(&kthread_lock);
+ schedule_timeout_interruptible(
+ usecs_to_jiffies(kthread_sleep));
+ } else
+ wait_event_interruptible(kthread_wait,
+ ksmd_flags & ksm_control_flags_run ||
+ kthread_should_stop());
+ }
+ return 0;
+}
+
+static int __init ksm_init(void)
+{
+ int r;
+
+ r = ksm_slab_init();
+ if (r)
+ goto out;
+
+ r = page_hash_init();
+ if (r)
+ goto out_free1;
+
+ r = rmap_hash_init();
+ if (r)
+ goto out_free2;
+
+ r = sha1_hash_init();
+ if (r)
+ goto out_free3;
+
+ spin_lock_init(&hash_lock);
+
+ kthread = kthread_run(kthread_ksm_scan_thread, NULL, "kksmd");
+ if (IS_ERR(kthread)) {
+ printk(KERN_ERR "ksm: creating kthread failed\n");
+ r = PTR_ERR(kthread);
+ goto out_free4;
+ }
+
+ r = misc_register(&ksm_dev);
+ if (r) {
+ printk(KERN_ERR "ksm: misc device register failed\n");
+ goto out_free5;
+ }
+
+ printk(KERN_WARNING "ksm loaded\n");
+ return 0;
+
+out_free5:
+ kthread_stop(kthread);
+out_free4:
+ sha1_hash_free();
+out_free3:
+ rmap_hash_free();
+out_free2:
+ page_hash_free();
+out_free1:
+ ksm_slab_free();
+out:
+ return r;
+}
+
+static void __exit ksm_exit(void)
+{
+ misc_deregister(&ksm_dev);
+ ksmd_flags = ksm_control_flags_run;
+ kthread_stop(kthread);
+ if (tfm)
+ crypto_free_hash(tfm);
+ sha1_hash_free();
+ rmap_hash_free();
+ page_hash_free();
+ ksm_slab_free();
+}
+
+module_init(ksm_init)
+module_exit(ksm_exit)
--
1.6.0.3

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