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authorMatthew Wilcox <willy@linux.intel.com>2015-09-08 14:58:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-08 15:35:28 -0700
commit844f35db1088dd1a9de37b53d4d823626232bd19 (patch)
tree69eed4135e8653b5304e211ee8734ee73639b28e /fs
parent5cad465d7fa646bad3d677df276bfc8e2ad709e3 (diff)
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: Matthew 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/dax.c152
1 files changed, 152 insertions, 0 deletions
diff --git a/fs/dax.c b/fs/dax.c
index a7f77e1fa18c..15f8ffc13fa6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -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

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