[PATCH v4 08/12] dax: remove dax_pmd_fault()

Ross Zwisler
2016-09-29T22:51:16Z

dax_pmd_fault() is the old struct buffer_head + get_block_t based 2 MiB DAX
fault handler. This fault handler has been disabled for several kernel
releases, and support for PMDs will be reintroduced using the struct iomap
interface instead.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
fs/dax.c | 213 ----------------------------------------------------
include/linux/dax.h | 6 +-
2 files changed, 1 insertion(+), 218 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 406feea..b5e7b13 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -909,219 +909,6 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
EXPORT_SYMBOL_GPL(dax_fault);

-#if defined(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)
-
-static void __dax_dbg(struct buffer_head *bh, unsigned long address,
- const char *reason, const char *fn)
-{
- if (bh) {
- char bname[BDEVNAME_SIZE];
- bdevname(bh->b_bdev, bname);
- pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
- "length %zd fallback: %s\n", fn, current->comm,
- address, bname, bh->b_state, (u64)bh->b_blocknr,
- bh->b_size, reason);
- } else {
- pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
- current->comm, address, reason);
- }
-}
-
-#define dax_pmd_dbg(bh, address, reason) __dax_dbg(bh, address, reason, "dax_pmd")
-
-/**
- * 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)
-{
- 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;
- struct block_device *bdev;
- pgoff_t size, pgoff;
- sector_t block;
- int result = 0;
- bool alloc = false;
-
- /* dax pmd mappings require pfn_t_devmap() */
- if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
- return VM_FAULT_FALLBACK;
-
- /* Fall back to PTEs if we're going to COW */
- if (write && !(vma->vm_flags & VM_SHARED)) {
- split_huge_pmd(vma, pmd, address);
- dax_pmd_dbg(NULL, address, "cow write");
- return VM_FAULT_FALLBACK;
- }
- /* If the PMD would extend outside the VMA */
- if (pmd_addr < vma->vm_start) {
- dax_pmd_dbg(NULL, address, "vma start unaligned");
- return VM_FAULT_FALLBACK;
- }
- if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
- dax_pmd_dbg(NULL, address, "vma end unaligned");
- return VM_FAULT_FALLBACK;
- }
-
- pgoff = linear_page_index(vma, pmd_addr);
- 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) {
- dax_pmd_dbg(NULL, address,
- "offset + huge page size > file size");
- return VM_FAULT_FALLBACK;
- }
-
- memset(&bh, 0, sizeof(bh));
- bh.b_bdev = inode->i_sb->s_bdev;
- block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
-
- bh.b_size = PMD_SIZE;
-
- if (get_block(inode, block, &bh, 0) != 0)
- return VM_FAULT_SIGBUS;
-
- if (!buffer_mapped(&bh) && write) {
- if (get_block(inode, block, &bh, 1) != 0)
- return VM_FAULT_SIGBUS;
- alloc = true;
- WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
- }
-
- bdev = bh.b_bdev;
-
- if (bh.b_size < PMD_SIZE) {
- dax_pmd_dbg(&bh, address, "allocated block too small");
- return VM_FAULT_FALLBACK;
- }
-
- /*
- * If we allocated new storage, make sure no process has any
- * zero pages covering this hole
- */
- if (alloc) {
- loff_t lstart = pgoff << PAGE_SHIFT;
- loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */
-
- truncate_pagecache_range(inode, lstart, lend);
- }
-
- if (!write && !buffer_mapped(&bh)) {
- spinlock_t *ptl;
- pmd_t entry;
- struct page *zero_page = get_huge_zero_page();
-
- if (unlikely(!zero_page)) {
- dax_pmd_dbg(&bh, address, "no zero page");
- goto fallback;
- }
-
- ptl = pmd_lock(vma->vm_mm, pmd);
- if (!pmd_none(*pmd)) {
- spin_unlock(ptl);
- dax_pmd_dbg(&bh, address, "pmd already present");
- goto fallback;
- }
-
- dev_dbg(part_to_dev(bdev->bd_part),
- "%s: %s addr: %lx pfn: <zero> sect: %llx\n",
- __func__, current->comm, address,
- (unsigned long long) to_sector(&bh, inode));
-
- entry = mk_pmd(zero_page, vma->vm_page_prot);
- entry = pmd_mkhuge(entry);
- set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
- result = VM_FAULT_NOPAGE;
- spin_unlock(ptl);
- } else {
- struct blk_dax_ctl dax = {
- .sector = to_sector(&bh, inode),
- .size = PMD_SIZE,
- };
- long length = dax_map_atomic(bdev, &dax);
-
- if (length < 0) {
- dax_pmd_dbg(&bh, address, "dax-error fallback");
- goto fallback;
- }
- if (length < PMD_SIZE) {
- dax_pmd_dbg(&bh, address, "dax-length too small");
- dax_unmap_atomic(bdev, &dax);
- goto fallback;
- }
- if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
- dax_pmd_dbg(&bh, address, "pfn unaligned");
- dax_unmap_atomic(bdev, &dax);
- goto fallback;
- }
-
- if (!pfn_t_devmap(dax.pfn)) {
- dax_unmap_atomic(bdev, &dax);
- dax_pmd_dbg(&bh, address, "pfn not in memmap");
- goto fallback;
- }
- dax_unmap_atomic(bdev, &dax);
-
- /*
- * For PTE faults we insert a radix tree entry for reads, and
- * leave it clean. Then on the first write we dirty the radix
- * tree entry via the dax_pfn_mkwrite() path. This sequence
- * allows the dax_pfn_mkwrite() call to be simpler and avoid a
- * call into get_block() to translate the pgoff to a sector in
- * order to be able to create a new radix tree entry.
- *
- * The PMD path doesn't have an equivalent to
- * dax_pfn_mkwrite(), though, so for a read followed by a
- * write we traverse all the way through dax_pmd_fault()
- * twice. This means we can just skip inserting a radix tree
- * entry completely on the initial read and just wait until
- * the write to insert a dirty entry.
- */
- if (write) {
- /*
- * We should insert radix-tree entry and dirty it here.
- * For now this is broken...
- */
- }
-
- dev_dbg(part_to_dev(bdev->bd_part),
- "%s: %s addr: %lx pfn: %lx sect: %llx\n",
- __func__, current->comm, address,
- pfn_t_to_pfn(dax.pfn),
- (unsigned long long) dax.sector);
- result |= vmf_insert_pfn_pmd(vma, address, pmd,
- dax.pfn, write);
- }
-
- out:
- return result;
-
- fallback:
- count_vm_event(THP_FAULT_FALLBACK);
- result = VM_FAULT_FALLBACK;
- goto out;
-}
-EXPORT_SYMBOL_GPL(dax_pmd_fault);
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
-
/**
* 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 4065601..d9a8350 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -48,16 +48,12 @@ static inline int __dax_zero_page_range(struct block_device *bdev,
}
#endif

-#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
-int dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
- unsigned int flags, get_block_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)
{
return VM_FAULT_FALLBACK;
}
-#endif
+
int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
#define dax_mkwrite(vma, vmf, gb) dax_fault(vma, vmf, gb)

--
2.7.4