I am sending out the latest set of patches for hugetlb demand faulting.
I've incorporated all the feedback I've received from previous
discussions and I think this is ready for some more widespread testing.
Is anyone opposed to spinning this in -mm as it stands?
The three patches:
1) Remove a get_user_pages() optimization that is no longer valid for
demand faulting
2) Move fault logic from hugetlb_prefault() to hugetlb_pte_fault()
3) Apply a simple overcommit check so demand fault accounting behaves
in a manner in line with how prefault worked
Diffed against 2.6.13-git6
Initial Post (Thu, 18 Aug 2005)
In preparation for hugetlb demand faulting, remove this get_user_pages()
optimization. Since huge pages will no longer be prefaulted, we can't assume
that the huge ptes are established and hence, calling follow_hugetlb_page() is
not valid.
With the follow_hugetlb_page() call removed, the normal code path will be
triggered. follow_page() will either use follow_huge_addr() or
follow_huge_pmd() to check for a previously faulted "page" to return. When
this fails (ie. with demand faults), __handle_mm_fault() gets called which
invokes the hugetlb_fault() handler to instantiate the huge page.
This patch doesn't make a lot of sense by itself, but I've broken it out to
facilitate discussion on this specific element of the demand fault changes.
While coding this up, I referenced previous discussion on this topic starting
at http://lkml.org/lkml/2004/4/13/176 , which contains more opinions about the
correctness of this approach.
Diffed against 2.6.13-git6
Signed-off-by: Adam Litke <[email protected]>
---
memory.c | 5 -----
1 files changed, 5 deletions(-)
diff -upN reference/mm/memory.c current/mm/memory.c
--- reference/mm/memory.c
+++ current/mm/memory.c
@@ -949,11 +949,6 @@ int get_user_pages(struct task_struct *t
|| !(flags & vma->vm_flags))
return i ? : -EFAULT;
- if (is_vm_hugetlb_page(vma)) {
- i = follow_hugetlb_page(mm, vma, pages, vmas,
- &start, &len, i);
- continue;
- }
spin_lock(&mm->page_table_lock);
do {
int write_access = write;
Below is a patch to implement demand faulting for huge pages. The main
motivation for changing from prefaulting to demand faulting is so that
huge page memory areas can be allocated according to NUMA policy.
Thanks to consolidated hugetlb code, switching the behavior requires changing
only one fault handler. The bulk of the patch just moves the logic from
hugelb_prefault() to hugetlb_pte_fault().
Diffed against 2.6.13-git6
Signed-off-by: Adam Litke <[email protected]>
---
fs/hugetlbfs/inode.c | 6 --
include/linux/hugetlb.h | 2
mm/hugetlb.c | 137 +++++++++++++++++++++++++++---------------------
mm/memory.c | 2
4 files changed, 82 insertions(+), 65 deletions(-)
diff -upN reference/fs/hugetlbfs/inode.c current/fs/hugetlbfs/inode.c
--- reference/fs/hugetlbfs/inode.c
+++ current/fs/hugetlbfs/inode.c
@@ -48,7 +48,6 @@ int sysctl_hugetlb_shm_group;
static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
struct inode *inode = file->f_dentry->d_inode;
- struct address_space *mapping = inode->i_mapping;
loff_t len, vma_len;
int ret;
@@ -79,10 +78,7 @@ static int hugetlbfs_file_mmap(struct fi
if (!(vma->vm_flags & VM_WRITE) && len > inode->i_size)
goto out;
- ret = hugetlb_prefault(mapping, vma);
- if (ret)
- goto out;
-
+ ret = 0;
if (inode->i_size < len)
inode->i_size = len;
out:
diff -upN reference/include/linux/hugetlb.h current/include/linux/hugetlb.h
--- reference/include/linux/hugetlb.h
+++ current/include/linux/hugetlb.h
@@ -25,6 +25,8 @@ int is_hugepage_mem_enough(size_t);
unsigned long hugetlb_total_pages(void);
struct page *alloc_huge_page(void);
void free_huge_page(struct page *);
+int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct * vma,
+ unsigned long address, int write_access);
extern unsigned long max_huge_pages;
extern const unsigned long hugetlb_zero, hugetlb_infinity;
diff -upN reference/mm/hugetlb.c current/mm/hugetlb.c
--- reference/mm/hugetlb.c
+++ current/mm/hugetlb.c
@@ -277,18 +277,20 @@ int copy_hugetlb_page_range(struct mm_st
unsigned long addr = vma->vm_start;
unsigned long end = vma->vm_end;
- while (addr < end) {
+ for (; addr < end; addr += HPAGE_SIZE) {
+ src_pte = huge_pte_offset(src, addr);
+ if (!src_pte || pte_none(*src_pte))
+ continue;
+
dst_pte = huge_pte_alloc(dst, addr);
if (!dst_pte)
goto nomem;
- src_pte = huge_pte_offset(src, addr);
- BUG_ON(!src_pte || pte_none(*src_pte)); /* prefaulted */
+ BUG_ON(!src_pte);
entry = *src_pte;
ptepage = pte_page(entry);
get_page(ptepage);
add_mm_counter(dst, rss, HPAGE_SIZE / PAGE_SIZE);
set_huge_pte_at(dst, addr, dst_pte, entry);
- addr += HPAGE_SIZE;
}
return 0;
@@ -338,61 +340,6 @@ void zap_hugepage_range(struct vm_area_s
spin_unlock(&mm->page_table_lock);
}
-int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
-{
- struct mm_struct *mm = current->mm;
- unsigned long addr;
- int ret = 0;
-
- WARN_ON(!is_vm_hugetlb_page(vma));
- BUG_ON(vma->vm_start & ~HPAGE_MASK);
- BUG_ON(vma->vm_end & ~HPAGE_MASK);
-
- hugetlb_prefault_arch_hook(mm);
-
- spin_lock(&mm->page_table_lock);
- for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
- unsigned long idx;
- pte_t *pte = huge_pte_alloc(mm, addr);
- struct page *page;
-
- if (!pte) {
- ret = -ENOMEM;
- goto out;
- }
-
- idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
- + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
- page = find_get_page(mapping, idx);
- if (!page) {
- /* charge the fs quota first */
- if (hugetlb_get_quota(mapping)) {
- ret = -ENOMEM;
- goto out;
- }
- page = alloc_huge_page();
- if (!page) {
- hugetlb_put_quota(mapping);
- ret = -ENOMEM;
- goto out;
- }
- ret = add_to_page_cache(page, mapping, idx, GFP_ATOMIC);
- if (! ret) {
- unlock_page(page);
- } else {
- hugetlb_put_quota(mapping);
- free_huge_page(page);
- goto out;
- }
- }
- add_mm_counter(mm, rss, HPAGE_SIZE / PAGE_SIZE);
- set_huge_pte_at(mm, addr, pte, make_huge_pte(vma, page));
- }
-out:
- spin_unlock(&mm->page_table_lock);
- return ret;
-}
-
int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
struct page **pages, struct vm_area_struct **vmas,
unsigned long *position, int *length, int i)
@@ -440,3 +387,75 @@ int follow_hugetlb_page(struct mm_struct
return i;
}
+
+int hugetlb_pte_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, int write_access)
+{
+ int ret = VM_FAULT_MINOR;
+ unsigned long idx;
+ pte_t *pte;
+ struct page *page;
+ struct address_space *mapping;
+
+ BUG_ON(vma->vm_start & ~HPAGE_MASK);
+ BUG_ON(vma->vm_end & ~HPAGE_MASK);
+ BUG_ON(!vma->vm_file);
+
+ pte = huge_pte_alloc(mm, address);
+ if (!pte) {
+ ret = VM_FAULT_SIGBUS;
+ goto out;
+ }
+ if (! pte_none(*pte))
+ goto flush;
+
+ mapping = vma->vm_file->f_mapping;
+ idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
+ + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
+retry:
+ page = find_get_page(mapping, idx);
+ if (!page) {
+ /* charge the fs quota first */
+ if (hugetlb_get_quota(mapping)) {
+ ret = VM_FAULT_SIGBUS;
+ goto out;
+ }
+ page = alloc_huge_page();
+ if (!page) {
+ hugetlb_put_quota(mapping);
+ ret = VM_FAULT_SIGBUS;
+ goto out;
+ }
+ if (add_to_page_cache(page, mapping, idx, GFP_ATOMIC)) {
+ put_page(page);
+ goto retry;
+ }
+ unlock_page(page);
+ }
+ add_mm_counter(mm, rss, HPAGE_SIZE / PAGE_SIZE);
+ set_huge_pte_at(mm, address, pte, make_huge_pte(vma, page));
+flush:
+ flush_tlb_page(vma, address);
+out:
+ return ret;
+}
+
+int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, int write_access)
+{
+ pte_t *ptep;
+ int rc = VM_FAULT_MINOR;
+
+ spin_lock(&mm->page_table_lock);
+
+ ptep = huge_pte_alloc(mm, address & HPAGE_MASK);
+ if (! ptep) {
+ rc = VM_FAULT_SIGBUS;
+ goto out;
+ }
+ if (pte_none(*ptep))
+ rc = hugetlb_pte_fault(mm, vma, address, write_access);
+out:
+ spin_unlock(&mm->page_table_lock);
+ return rc;
+}
diff -upN reference/mm/memory.c current/mm/memory.c
--- reference/mm/memory.c
+++ current/mm/memory.c
@@ -2041,7 +2041,7 @@ int __handle_mm_fault(struct mm_struct *
inc_page_state(pgfault);
if (is_vm_hugetlb_page(vma))
- return VM_FAULT_SIGBUS; /* mapping truncation does this. */
+ return hugetlb_fault(mm, vma, address, write_access);
/*
* We need the page table lock to synchronize with kswapd
Initial Post (Thu, 18 Aug 2005)
Basic overcommit checking for hugetlb_file_map() based on an implementation
used with demand faulting in SLES9.
Since demand faulting can't guarantee the availability of pages at mmap time,
this patch implements a basic sanity check to ensure that the number of huge
pages required to satisfy the mmap are currently available. Despite the
obvious race, I think it is a good start on doing proper accounting. I'd like
to work towards an accounting system that mimics the semantics of normal pages
(especially for the MAP_PRIVATE/COW case). That work is underway and builds on
what this patch starts.
Huge page shared memory segments are simpler and still maintain their commit on
shmget semantics.
Diffed against 2.6.13-git6
Signed-off-by: Adam Litke <[email protected]>
---
inode.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 47 insertions(+)
diff -upN reference/fs/hugetlbfs/inode.c current/fs/hugetlbfs/inode.c
--- reference/fs/hugetlbfs/inode.c
+++ current/fs/hugetlbfs/inode.c
@@ -45,9 +45,51 @@ static struct backing_dev_info hugetlbfs
int sysctl_hugetlb_shm_group;
+static void huge_pagevec_release(struct pagevec *pvec);
+
+unsigned long
+huge_pages_needed(struct address_space *mapping, struct vm_area_struct *vma)
+{
+ int i;
+ struct pagevec pvec;
+ unsigned long start = vma->vm_start;
+ unsigned long end = vma->vm_end;
+ unsigned long hugepages = (end - start) >> HPAGE_SHIFT;
+ pgoff_t next = vma->vm_pgoff;
+ pgoff_t endpg = next + ((end - start) >> PAGE_SHIFT);
+ struct inode *inode = vma->vm_file->f_dentry->d_inode;
+
+ /*
+ * Shared memory segments are accounted for at shget time,
+ * not at shmat (when the mapping is actually created) so
+ * check here if the memory has already been accounted for.
+ */
+ if (inode->i_blocks != 0)
+ return 0;
+
+ pagevec_init(&pvec, 0);
+ while (next < endpg) {
+ if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE))
+ break;
+ for (i = 0; i < pagevec_count(&pvec); i++) {
+ struct page *page = pvec.pages[i];
+ if (page->index > next)
+ next = page->index;
+ if (page->index >= endpg)
+ break;
+ next++;
+ hugepages--;
+ }
+ huge_pagevec_release(&pvec);
+ }
+ return hugepages << HPAGE_SHIFT;
+}
+
static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
struct inode *inode = file->f_dentry->d_inode;
+ struct address_space *mapping = inode->i_mapping;
+ unsigned long bytes;
loff_t len, vma_len;
int ret;
@@ -66,6 +108,10 @@ static int hugetlbfs_file_mmap(struct fi
if (vma->vm_end - vma->vm_start < HPAGE_SIZE)
return -EINVAL;
+ bytes = huge_pages_needed(mapping, vma);
+ if (!is_hugepage_mem_enough(bytes))
+ return -ENOMEM;
+
vma_len = (loff_t)(vma->vm_end - vma->vm_start);
down(&inode->i_sem);
@@ -794,6 +840,7 @@ struct file *hugetlb_zero_setup(size_t s
d_instantiate(dentry, inode);
inode->i_size = size;
inode->i_nlink = 0;
+ inode->i_blocks = 1;
file->f_vfsmnt = mntget(hugetlbfs_vfsmount);
file->f_dentry = dentry;
file->f_mapping = inode->i_mapping;