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

From: Jan Kara
Date: Mon Oct 03 2016 - 05:56:59 EST

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On Thu 29-09-16 16:49:26, Ross Zwisler wrote:
> 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@xxxxxxxxxxxxxxx>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

Honza

> ---
> 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
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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