Commit 844f35db authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Linus Torvalds

dax: add huge page fault support

This is the support code for DAX-enabled filesystems to allow them to
provide huge pages in response to faults.
Signed-off-by: default avatarMatthew Wilcox <willy@linux.intel.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5cad465d
......@@ -60,9 +60,10 @@ Filesystem support consists of
- implementing the direct_IO address space operation, and calling
dax_do_io() instead of blockdev_direct_IO() if S_DAX is set
- implementing an mmap file operation for DAX files which sets the
VM_MIXEDMAP flag on the VMA, and setting the vm_ops to include handlers
for fault and page_mkwrite (which should probably call dax_fault() and
dax_mkwrite(), passing the appropriate get_block() callback)
VM_MIXEDMAP and VM_HUGEPAGE flags on the VMA, and setting the vm_ops to
include handlers for fault, pmd_fault and page_mkwrite (which should
probably call dax_fault(), dax_pmd_fault() and dax_mkwrite(), passing the
appropriate get_block() callback)
- calling dax_truncate_page() instead of block_truncate_page() for DAX files
- calling dax_zero_page_range() instead of zero_user() for DAX files
- ensuring that there is sufficient locking between reads, writes,
......
......@@ -494,6 +494,158 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
EXPORT_SYMBOL_GPL(dax_fault);
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/*
* The 'colour' (ie low bits) within a PMD of a page offset. This comes up
* more often than one might expect in the below function.
*/
#define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmd, unsigned int flags, get_block_t get_block,
dax_iodone_t complete_unwritten)
{
struct file *file = vma->vm_file;
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
struct buffer_head bh;
unsigned blkbits = inode->i_blkbits;
unsigned long pmd_addr = address & PMD_MASK;
bool write = flags & FAULT_FLAG_WRITE;
long length;
void *kaddr;
pgoff_t size, pgoff;
sector_t block, sector;
unsigned long pfn;
int result = 0;
/* Fall back to PTEs if we're going to COW */
if (write && !(vma->vm_flags & VM_SHARED))
return VM_FAULT_FALLBACK;
/* If the PMD would extend outside the VMA */
if (pmd_addr < vma->vm_start)
return VM_FAULT_FALLBACK;
if ((pmd_addr + PMD_SIZE) > vma->vm_end)
return VM_FAULT_FALLBACK;
pgoff = ((pmd_addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (pgoff >= size)
return VM_FAULT_SIGBUS;
/* If the PMD would cover blocks out of the file */
if ((pgoff | PG_PMD_COLOUR) >= size)
return VM_FAULT_FALLBACK;
memset(&bh, 0, sizeof(bh));
block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
bh.b_size = PMD_SIZE;
length = get_block(inode, block, &bh, write);
if (length)
return VM_FAULT_SIGBUS;
i_mmap_lock_read(mapping);
/*
* If the filesystem isn't willing to tell us the length of a hole,
* just fall back to PTEs. Calling get_block 512 times in a loop
* would be silly.
*/
if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
goto fallback;
/* Guard against a race with truncate */
size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (pgoff >= size) {
result = VM_FAULT_SIGBUS;
goto out;
}
if ((pgoff | PG_PMD_COLOUR) >= size)
goto fallback;
if (is_huge_zero_pmd(*pmd))
unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {
bool set;
spinlock_t *ptl;
struct mm_struct *mm = vma->vm_mm;
struct page *zero_page = get_huge_zero_page();
if (unlikely(!zero_page))
goto fallback;
ptl = pmd_lock(mm, pmd);
set = set_huge_zero_page(NULL, mm, vma, pmd_addr, pmd,
zero_page);
spin_unlock(ptl);
result = VM_FAULT_NOPAGE;
} else {
sector = bh.b_blocknr << (blkbits - 9);
length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
bh.b_size);
if (length < 0) {
result = VM_FAULT_SIGBUS;
goto out;
}
if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
goto fallback;
if (buffer_unwritten(&bh) || buffer_new(&bh)) {
int i;
for (i = 0; i < PTRS_PER_PMD; i++)
clear_page(kaddr + i * PAGE_SIZE);
count_vm_event(PGMAJFAULT);
mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
result |= VM_FAULT_MAJOR;
}
result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
}
out:
i_mmap_unlock_read(mapping);
if (buffer_unwritten(&bh))
complete_unwritten(&bh, !(result & VM_FAULT_ERROR));
return result;
fallback:
count_vm_event(THP_FAULT_FALLBACK);
result = VM_FAULT_FALLBACK;
goto out;
}
EXPORT_SYMBOL_GPL(__dax_pmd_fault);
/**
* dax_pmd_fault - handle a PMD fault on a DAX file
* @vma: The virtual memory area where the fault occurred
* @vmf: The description of the fault
* @get_block: The filesystem method used to translate file offsets to blocks
*
* When a page fault occurs, filesystems may call this helper in their
* pmd_fault handler for DAX files.
*/
int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmd, unsigned int flags, get_block_t get_block,
dax_iodone_t complete_unwritten)
{
int result;
struct super_block *sb = file_inode(vma->vm_file)->i_sb;
if (flags & FAULT_FLAG_WRITE) {
sb_start_pagefault(sb);
file_update_time(vma->vm_file);
}
result = __dax_pmd_fault(vma, address, pmd, flags, get_block,
complete_unwritten);
if (flags & FAULT_FLAG_WRITE)
sb_end_pagefault(sb);
return result;
}
EXPORT_SYMBOL_GPL(dax_pmd_fault);
#endif /* CONFIG_TRANSPARENT_HUGEPAGES */
/**
* dax_pfn_mkwrite - handle first write to DAX page
* @vma: The virtual memory area where the fault occurred
......
......@@ -14,6 +14,20 @@ int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
dax_iodone_t);
int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
dax_iodone_t);
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
int dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
unsigned int flags, get_block_t, dax_iodone_t);
int __dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
unsigned int flags, get_block_t, dax_iodone_t);
#else
static inline int dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
pmd_t *pmd, unsigned int flags, get_block_t gb,
dax_iodone_t di)
{
return VM_FAULT_FALLBACK;
}
#define __dax_pmd_fault dax_pmd_fault
#endif
int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
#define dax_mkwrite(vma, vmf, gb, iod) dax_fault(vma, vmf, gb, iod)
#define __dax_mkwrite(vma, vmf, gb, iod) __dax_fault(vma, vmf, gb, iod)
......
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