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Date: Mon, 23 Dec 2013 15:41:13 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v4 21/22] Add support for pmd_faults
On Sun, Dec 22, 2013 at 04:49:48PM -0500, Matthew Wilcox wrote:
> Introduce the vm_ops ->pmd_fault handler, add a vm_insert_pfn_pmd function
> and create an xip_pmd_fault handler.
>
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@...el.com>
> ---
> fs/ext2/file.c | 9 ++++-
> fs/ext4/file.c | 9 ++++-
> fs/xip.c | 101 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 8 ++---
> include/linux/mm.h | 4 +++
> mm/memory.c | 50 +++++++++++++++++++++++---
> 6 files changed, 169 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 6e6e803..7d6e492 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -31,8 +31,15 @@ static int ext2_xip_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> return xip_fault(vma, vmf, ext2_get_block);
> }
>
> +static int ext2_xip_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> + pmd_t *pmd, unsigned int flags)
> +{
> + return xip_pmd_fault(vma, addr, pmd, flags, ext2_get_block);
> +}
> +
> static const struct vm_operations_struct ext2_xip_vm_ops = {
> .fault = ext2_xip_fault,
> + .pmd_fault = ext2_xip_pmd_fault,
> .remap_pages = generic_file_remap_pages,
> };
>
> @@ -43,7 +50,7 @@ static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
>
> file_accessed(file);
> vma->vm_ops = &ext2_xip_vm_ops;
> - vma->vm_flags |= VM_MIXEDMAP;
> + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
> return 0;
> }
> #else
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index d6ae6be..6211f56 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -205,8 +205,15 @@ static int ext4_xip_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> /* Is this the right get_block? */
> }
>
> +static int ext4_xip_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> + pmd_t *pmd, unsigned int flags)
> +{
> + return xip_pmd_fault(vma, addr, pmd, flags, ext4_get_block);
> +}
> +
> static const struct vm_operations_struct ext4_xip_vm_ops = {
> .fault = ext4_xip_fault,
> + .pmd_fault = ext4_xip_pmd_fault,
> .remap_pages = generic_file_remap_pages,
> };
> #else
> @@ -224,7 +231,7 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
> file_accessed(file);
> if (IS_XIP(file_inode(file))) {
> vma->vm_ops = &ext4_xip_vm_ops;
> - vma->vm_flags |= VM_MIXEDMAP;
> + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
> } else {
> vma->vm_ops = &ext4_file_vm_ops;
> }
> diff --git a/fs/xip.c b/fs/xip.c
> index e6e52ee..d032838 100644
> --- a/fs/xip.c
> +++ b/fs/xip.c
> @@ -273,6 +273,107 @@ int xip_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> }
> EXPORT_SYMBOL_GPL(xip_fault);
>
> +/*
> + * 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)
> +
> +/*
> + * We are willing to use a PMD mapping to cover the end of a file if it
> + * could be mapped by a complete PMD's worth of PTEs. That is, the last
> + * part of the file might be slightly smaller than PMD_SIZE, but as long
> + * as it's at least (PMD_SIZE - PAGE_SIZE + 1) bytes long, we allow the
> + * PMD mapping.
> + */
> +static int do_xip_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 inode *inode = file_inode(file);
> + struct address_space *mapping = file->f_mapping;
> + struct buffer_head bh;
> + long length;
> + pgoff_t size, pgoff;
> + sector_t block;
> + unsigned long pfn;
> +
> + /* Fall back to PTEs if we're going to COW */
> + if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
> + return VM_FAULT_FALLBACK;
Why?
> + pgoff = ((address - 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 ((pgoff | PG_PMD_COLOUR) >= size)
> + return VM_FAULT_FALLBACK;
I don't think it's necessary to fallback in this case.
Do you care about SIGBUS behaviour or what?
> + memset(&bh, 0, sizeof(bh));
> + block = ((sector_t)pgoff & ~PG_PMD_COLOUR) <<
> + (PAGE_SHIFT - inode->i_blkbits);
> +
> + /* Start by seeing if we already have an allocated block */
> + bh.b_size = PMD_SIZE;
> + length = get_block(inode, block, &bh, 0);
> + if (length)
> + return VM_FAULT_SIGBUS;
> + if (buffer_mapped(&bh) && bh.b_size == PMD_SIZE)
> + goto insert;
> +
> + /* Next, try to allocate the whole thing */
> + bh.b_size = PMD_SIZE;
> + length = get_block(inode, block, &bh, 1);
> + if (length)
> + return VM_FAULT_SIGBUS;
> + if (bh.b_size == PMD_SIZE)
> + goto insert;
> +
> + return VM_FAULT_FALLBACK;
> +
> + insert:
> + length = xip_get_pfn(inode, &bh, &pfn);
> + if (length < 0)
> + return VM_FAULT_SIGBUS;
> + if (length < PMD_SIZE)
> + return VM_FAULT_FALLBACK;
> + if (pfn & PG_PMD_COLOUR)
> + return VM_FAULT_FALLBACK; /* not aligned */
Without assistance from get_unmapped_area() you will hit this all the time
(511 of 512 on x86_64).
And the check should be moved before get_block(), I think.
> +
> + /* We must recheck i_size under i_mmap_mutex */
> + mutex_lock(&mapping->i_mmap_mutex);
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if ((pgoff | PG_PMD_COLOUR) < size)
> + length = vm_insert_pfn_pmd(vma, address, pmd, pfn);
> + mutex_unlock(&mapping->i_mmap_mutex);
> +
> + if (pgoff >= size)
> + return VM_FAULT_SIGBUS;
> + if ((pgoff | PG_PMD_COLOUR) >= size)
> + return VM_FAULT_FALLBACK;
> + if (length == -ENOMEM)
> + return VM_FAULT_OOM;
> + /* -EBUSY is fine, somebody else faulted on the same PMD */
> + if (length != -EBUSY)
> + BUG_ON(length);
> + return VM_FAULT_NOPAGE;
> +}
> +
> +int xip_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> + pmd_t *pmd, unsigned int flags, get_block_t get_block)
> +{
> + int result;
> + struct super_block *sb = file_inode(vma->vm_file)->i_sb;
> +
> + sb_start_pagefault(sb);
> + file_update_time(vma->vm_file);
> + result = do_xip_pmd_fault(vma, address, pmd, flags, get_block);
> + sb_end_pagefault(sb);
> +
> + return result;
> +}
> +EXPORT_SYMBOL_GPL(xip_pmd_fault);
> +
> /**
> * xip_zero_page_range - zero a range within a page of an XIP file
> * @inode: The file being truncated
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3a4a217..e789218 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2513,6 +2513,8 @@ int xip_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
> ssize_t xip_do_io(int rw, struct kiocb *, struct inode *, const struct iovec *,
> loff_t, unsigned segs, get_block_t, dio_iodone_t, int flags);
> int xip_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
> +int xip_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
> + unsigned int flags, get_block_t);
> #else
> static inline int xip_clear_blocks(struct inode *i, sector_t blk, long sz)
> {
> @@ -2531,12 +2533,6 @@ static inline ssize_t xip_do_io(int rw, struct kiocb *iocb, struct inode *inode,
> {
> return -ENOTTY;
> }
> -
> -static inline int xip_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> - get_block_t gb)
> -{
> - return 0;
> -}
> #endif
>
> /* PAGE_CACHE_ALIGN is defined in pagemap.h */
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e07c57c..d48913d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -212,6 +212,8 @@ struct vm_operations_struct {
> void (*open)(struct vm_area_struct * area);
> void (*close)(struct vm_area_struct * area);
> int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
> + int (*pmd_fault)(struct vm_area_struct *, unsigned long address,
> + pmd_t *, unsigned int flags);
>
> /* notification that a previously read-only page is about to become
> * writable, if an error is returned it will cause a SIGBUS */
> @@ -1857,6 +1859,8 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> unsigned long pfn);
> int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
> unsigned long pfn);
> +int vm_insert_pfn_pmd(struct vm_area_struct *, unsigned long addr, pmd_t *,
> + unsigned long pfn);
> int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
>
>
> diff --git a/mm/memory.c b/mm/memory.c
> index ecd63fe..0d332cf 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2249,6 +2249,41 @@ int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
> }
> EXPORT_SYMBOL(vm_insert_mixed);
>
> +static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> + pmd_t *pmd, unsigned long pfn, pgprot_t prot)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + int retval;
> + pmd_t entry;
> + spinlock_t *ptl;
> +
> + ptl = pmd_lock(mm, pmd);
> + retval = -EBUSY;
> + if (!pmd_none(*pmd))
> + goto out_unlock;
> +
> + /* Ok, finally just insert the thing.. */
> + entry = pfn_pmd(pfn, prot); /* XXX: pmd_mkspecial? */
> + set_pmd_at(mm, addr, pmd, entry);
> + update_mmu_cache_pmd(vma, addr, pmd);
Here you need to allocate pgtable and deposit it to be able to split the page.
> + retval = 0;
> + out_unlock:
> + spin_unlock(ptl);
> + return retval;
> +}
> +
> +int vm_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> + pmd_t *pmd, unsigned long pfn)
> +{
> + BUG_ON(!(vma->vm_flags & VM_MIXEDMAP));
> +
> + if (addr < vma->vm_start || addr >= vma->vm_end)
> + return -EFAULT;
> + return insert_pfn_pmd(vma, addr, pmd, pfn, vma->vm_page_prot);
> +}
> +EXPORT_SYMBOL(vm_insert_pfn_pmd);
> +
> /*
> * maps a range of physical memory into the requested pages. the old
> * mappings are removed. any references to nonexistent pages results
> @@ -3630,6 +3665,16 @@ out:
> return 0;
> }
>
> +static int create_huge_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
> + unsigned long address, pmd_t *pmd, unsigned int flags)
> +{
> + if (!vma->vm_ops)
> + return do_huge_pmd_anonymous_page(mm, vma, address, pmd, flags);
> + if (vma->vm_ops->pmd_fault)
> + return vma->vm_ops->pmd_fault(vma, address, pmd, flags);
> + return VM_FAULT_FALLBACK;
> +}
> +
> /*
> * These routines also need to handle stuff like marking pages dirty
> * and/or accessed for architectures that don't do it in hardware (most
> @@ -3722,10 +3767,7 @@ retry:
> if (!pmd)
> return VM_FAULT_OOM;
> if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
> - int ret = VM_FAULT_FALLBACK;
> - if (!vma->vm_ops)
> - ret = do_huge_pmd_anonymous_page(mm, vma, address,
> - pmd, flags);
> + int ret = create_huge_pmd(mm, vma, address, pmd, flags);
> if (!(ret & VM_FAULT_FALLBACK))
> return ret;
> } else {
> --
> 1.8.4.rc3
>
> --
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--
Kirill A. Shutemov
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