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Date: Fri, 10 Jul 2015 16:29:22 -0400
From: Matthew Wilcox <matthew.r.wilcox@...el.com>
To: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Cc: Matthew Wilcox <willy@...ux.intel.com>
Subject: [PATCH 07/10] dax: Add huge page fault support
From: Matthew Wilcox <willy@...ux.intel.com>
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@...ux.intel.com>
---
Documentation/filesystems/dax.txt | 7 +-
fs/dax.c | 152 ++++++++++++++++++++++++++++++++++++++
include/linux/dax.h | 14 ++++
3 files changed, 170 insertions(+), 3 deletions(-)
diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 7af2851..7bde640 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -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,
diff --git a/fs/dax.c b/fs/dax.c
index c3e21cc..20cf3b0 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -484,6 +484,158 @@ 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
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 9b51f9d..b415e52 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -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)
--
2.1.4
--
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