[PATCHv8 23/32] shmem: get_unmapped_area align huge page

Kirill A. Shutemov
2016-05-12T15:46:05Z

From: Hugh Dickins <hughd@google.com>

Provide a shmem_get_unmapped_area method in file_operations, called
at mmap time to decide the mapping address. It could be conditional
on CONFIG_TRANSPARENT_HUGEPAGE, but save #ifdefs in other places by
making it unconditional.

shmem_get_unmapped_area() first calls the usual mm->get_unmapped_area
(which we treat as a black box, highly dependent on architecture and
config and executable layout). Lots of conditions, and in most cases
it just goes with the address that chose; but when our huge stars are
rightly aligned, yet that did not provide a suitable address, go back
to ask for a larger arena, within which to align the mapping suitably.

There have to be some direct calls to shmem_get_unmapped_area(),
not via the file_operations: because of the way shmem_zero_setup()
is called to create a shmem object late in the mmap sequence, when
MAP_SHARED is requested with MAP_ANONYMOUS or /dev/zero. Though
this only matters when /proc/sys/vm/shmem_huge has been set.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
drivers/char/mem.c | 24 ++++++++++++
include/linux/shmem_fs.h | 2 +
ipc/shm.c | 6 ++-
mm/mmap.c | 16 +++++++-
mm/shmem.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 142 insertions(+), 4 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 71025c2f6bbb..9656f1095c19 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -22,6 +22,7 @@
#include <linux/device.h>
#include <linux/highmem.h>
#include <linux/backing-dev.h>
+#include <linux/shmem_fs.h>
#include <linux/splice.h>
#include <linux/pfn.h>
#include <linux/export.h>
@@ -661,6 +662,28 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma)
return 0;
}

+static unsigned long get_unmapped_area_zero(struct file *file,
+ unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+#ifdef CONFIG_MMU
+ if (flags & MAP_SHARED) {
+ /*
+ * mmap_zero() will call shmem_zero_setup() to create a file,
+ * so use shmem's get_unmapped_area in case it can be huge;
+ * and pass NULL for file as in mmap.c's get_unmapped_area(),
+ * so as not to confuse shmem with our handle on "/dev/zero".
+ */
+ return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
+ }
+
+ /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
+ return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
+#else
+ return -ENOSYS;
+#endif
+}
+
static ssize_t write_full(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
@@ -768,6 +791,7 @@ static const struct file_operations zero_fops = {
.read_iter = read_iter_zero,
.write_iter = write_iter_zero,
.mmap = mmap_zero,
+ .get_unmapped_area = get_unmapped_area_zero,
#ifndef CONFIG_MMU
.mmap_capabilities = zero_mmap_capabilities,
#endif
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 466f18c73a49..ff2de4bab61f 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -50,6 +50,8 @@ extern struct file *shmem_file_setup(const char *name,
extern struct file *shmem_kernel_file_setup(const char *name, loff_t size,
unsigned long flags);
extern int shmem_zero_setup(struct vm_area_struct *);
+extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
+ unsigned long len, unsigned long pgoff, unsigned long flags);
extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
extern bool shmem_mapping(struct address_space *mapping);
extern void shmem_unlock_mapping(struct address_space *mapping);
diff --git a/ipc/shm.c b/ipc/shm.c
index 331fc1b0b3c7..b1ed484eeda1 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -476,13 +476,15 @@ static const struct file_operations shm_file_operations = {
.mmap = shm_mmap,
.fsync = shm_fsync,
.release = shm_release,
-#ifndef CONFIG_MMU
.get_unmapped_area = shm_get_unmapped_area,
-#endif
.llseek = noop_llseek,
.fallocate = shm_fallocate,
};

+/*
+ * shm_file_operations_huge is now identical to shm_file_operations,
+ * but we keep it distinct for the sake of is_file_shm_hugepages().
+ */
static const struct file_operations shm_file_operations_huge = {
.mmap = shm_mmap,
.fsync = shm_fsync,
diff --git a/mm/mmap.c b/mm/mmap.c
index 0a68cf0b37e7..cc1fa2b0d14f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -25,6 +25,7 @@
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
+#include <linux/shmem_fs.h>
#include <linux/profile.h>
#include <linux/export.h>
#include <linux/mount.h>
@@ -1900,8 +1901,19 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
return -ENOMEM;

get_area = current->mm->get_unmapped_area;
- if (file && file->f_op->get_unmapped_area)
- get_area = file->f_op->get_unmapped_area;
+ if (file) {
+ if (file->f_op->get_unmapped_area)
+ get_area = file->f_op->get_unmapped_area;
+ } else if (flags & MAP_SHARED) {
+ /*
+ * mmap_region() will call shmem_zero_setup() to create a file,
+ * so use shmem's get_unmapped_area in case it can be huge.
+ * do_mmap_pgoff() will clear pgoff, so match alignment.
+ */
+ pgoff = 0;
+ get_area = shmem_get_unmapped_area;
+ }
+
addr = get_area(file, addr, len, pgoff, flags);
if (IS_ERR_VALUE(addr))
return addr;
diff --git a/mm/shmem.c b/mm/shmem.c
index 3a6349e9c186..929fbf2ac43f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1513,6 +1513,94 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
return ret;
}

+unsigned long shmem_get_unmapped_area(struct file *file,
+ unsigned long uaddr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+ unsigned long (*get_area)(struct file *,
+ unsigned long, unsigned long, unsigned long, unsigned long);
+ unsigned long addr;
+ unsigned long offset;
+ unsigned long inflated_len;
+ unsigned long inflated_addr;
+ unsigned long inflated_offset;
+
+ if (len > TASK_SIZE)
+ return -ENOMEM;
+
+ get_area = current->mm->get_unmapped_area;
+ addr = get_area(file, uaddr, len, pgoff, flags);
+
+ if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+ return addr;
+ if (IS_ERR_VALUE(addr))
+ return addr;
+ if (addr & ~PAGE_MASK)
+ return addr;
+ if (addr > TASK_SIZE - len)
+ return addr;
+
+ if (shmem_huge == SHMEM_HUGE_DENY)
+ return addr;
+ if (len < HPAGE_PMD_SIZE)
+ return addr;
+ if (flags & MAP_FIXED)
+ return addr;
+ /*
+ * Our priority is to support MAP_SHARED mapped hugely;
+ * and support MAP_PRIVATE mapped hugely too, until it is COWed.
+ * But if caller specified an address hint, respect that as before.
+ */
+ if (uaddr)
+ return addr;
+
+ if (shmem_huge != SHMEM_HUGE_FORCE) {
+ struct super_block *sb;
+
+ if (file) {
+ VM_BUG_ON(file->f_op != &shmem_file_operations);
+ sb = file_inode(file)->i_sb;
+ } else {
+ /*
+ * Called directly from mm/mmap.c, or drivers/char/mem.c
+ * for "/dev/zero", to create a shared anonymous object.
+ */
+ if (IS_ERR(shm_mnt))
+ return addr;
+ sb = shm_mnt->mnt_sb;
+ }
+ if (SHMEM_SB(sb)->huge != SHMEM_HUGE_NEVER)
+ return addr;
+ }
+
+ offset = (pgoff << PAGE_SHIFT) & (HPAGE_PMD_SIZE-1);
+ if (offset && offset + len < 2 * HPAGE_PMD_SIZE)
+ return addr;
+ if ((addr & (HPAGE_PMD_SIZE-1)) == offset)
+ return addr;
+
+ inflated_len = len + HPAGE_PMD_SIZE - PAGE_SIZE;
+ if (inflated_len > TASK_SIZE)
+ return addr;
+ if (inflated_len < len)
+ return addr;
+
+ inflated_addr = get_area(NULL, 0, inflated_len, 0, flags);
+ if (IS_ERR_VALUE(inflated_addr))
+ return addr;
+ if (inflated_addr & ~PAGE_MASK)
+ return addr;
+
+ inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
+ inflated_addr += offset - inflated_offset;
+ if (inflated_offset > offset)
+ inflated_addr += HPAGE_PMD_SIZE;
+
+ if (inflated_addr > TASK_SIZE - len)
+ return addr;
+ return inflated_addr;
+}
+
#ifdef CONFIG_NUMA
static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
{
@@ -3257,6 +3345,7 @@ static const struct address_space_operations shmem_aops = {

static const struct file_operations shmem_file_operations = {
.mmap = shmem_mmap,
+ .get_unmapped_area = shmem_get_unmapped_area,
#ifdef CONFIG_TMPFS
.llseek = shmem_file_llseek,
.read_iter = shmem_file_read_iter,
@@ -3492,6 +3581,15 @@ void shmem_unlock_mapping(struct address_space *mapping)
{
}

+#ifdef CONFIG_MMU
+unsigned long shmem_get_unmapped_area(struct file *file,
+ unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+ return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
+}
+#endif
+
void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
truncate_inode_pages_range(inode->i_mapping, lstart, lend);
--
2.8.1