On 25-Sep-2014 04:33:26 PM, Matthew Wilcox wrote:
> Instead of calling aops->get_xip_mem from the fault handler, the
> filesystem passes a get_block_t that is used to find the appropriate
> blocks.
>
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/dax.c | 232 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> fs/ext2/file.c | 35 +++++++-
> include/linux/fs.h | 4 +-
> mm/filemap_xip.c | 206 -----------------------------------------------
> 4 files changed, 268 insertions(+), 209 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 02e226f..ac5d3a6 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -19,9 +19,13 @@
> #include <linux/buffer_head.h>
> #include <linux/fs.h>
> #include <linux/genhd.h>
> +#include <linux/highmem.h>
> +#include <linux/memcontrol.h>
> +#include <linux/mm.h>
> #include <linux/mutex.h>
> #include <linux/sched.h>
> #include <linux/uio.h>
> +#include <linux/vmstat.h>
>
> int dax_clear_blocks(struct inode *inode, sector_t block, long size)
> {
> @@ -228,3 +232,231 @@ ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
> return retval;
> }
> EXPORT_SYMBOL_GPL(dax_do_io);
> +
> +/*
> + * The user has performed a load from a hole in the file. Allocating
> + * a new page in the file would cause excessive storage usage for
> + * workloads with sparse files. We allocate a page cache page instead.
> + * We'll kick it out of the page cache if it's ever written to,
> + * otherwise it will simply fall out of the page cache under memory
> + * pressure without ever having been dirtied.
Nice trick :)
> + */
> +static int dax_load_hole(struct address_space *mapping, struct page *page,
> + struct vm_fault *vmf)
> +{
> + unsigned long size;
> + struct inode *inode = mapping->host;
missing newline.
> + if (!page)
> + page = find_or_create_page(mapping, vmf->pgoff,
> + GFP_KERNEL | __GFP_ZERO);
> + if (!page)
> + return VM_FAULT_OOM;
> + /* Recheck i_size under page lock to avoid truncate race */
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if (vmf->pgoff >= size) {
> + unlock_page(page);
> + page_cache_release(page);
> + return VM_FAULT_SIGBUS;
> + }
> +
> + vmf->page = page;
> + return VM_FAULT_LOCKED;
> +}
> +
> +static int copy_user_bh(struct page *to, struct buffer_head *bh,
> + unsigned blkbits, unsigned long vaddr)
> +{
> + void *vfrom, *vto;
missing newline.
> + if (dax_get_addr(bh, &vfrom, blkbits) < 0)
> + return -EIO;
> + vto = kmap_atomic(to);
> + copy_user_page(vto, vfrom, vaddr, to);
> + kunmap_atomic(vto);
> + return 0;
> +}
> +
> +static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
> + struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + struct address_space *mapping = inode->i_mapping;
> + sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
> + unsigned long vaddr = (unsigned long)vmf->virtual_address;
> + void *addr;
> + unsigned long pfn;
> + pgoff_t size;
> + int error;
> +
> + mutex_lock(&mapping->i_mmap_mutex);
> +
> + /*
> + * Check truncate didn't happen while we were allocating a block.
> + * If it did, this block may or may not be still allocated to the
> + * file. We can't tell the filesystem to free it because we can't
> + * take i_mutex here. In the worst case, the file still has blocks
> + * allocated past the end of the file.
> + */
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if (unlikely(vmf->pgoff >= size)) {
> + error = -EIO;
> + goto out;
> + }
> +
> + error = bdev_direct_access(bh->b_bdev, sector, &addr, &pfn, bh->b_size);
> + if (error < 0)
> + goto out;
> + if (error < PAGE_SIZE) {
> + error = -EIO;
> + goto out;
> + }
> +
> + if (buffer_unwritten(bh) || buffer_new(bh))
> + clear_page(addr);
> +
> + error = vm_insert_mixed(vma, vaddr, pfn);
> +
> + out:
> + mutex_unlock(&mapping->i_mmap_mutex);
> +
> + if (bh->b_end_io)
> + bh->b_end_io(bh, 1);
> +
> + return error;
> +}
> +
> +static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> + 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 page *page;
> + struct buffer_head bh;
> + unsigned long vaddr = (unsigned long)vmf->virtual_address;
> + unsigned blkbits = inode->i_blkbits;
unsigned -> unsigned int
> + sector_t block;
> + pgoff_t size;
> + int error;
> + int major = 0;
> +
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if (vmf->pgoff >= size)
> + return VM_FAULT_SIGBUS;
> +
> + memset(&bh, 0, sizeof(bh));
> + block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
> + bh.b_size = PAGE_SIZE;
> +
> + repeat:
> + page = find_get_page(mapping, vmf->pgoff);
> + if (page) {
> + if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
> + page_cache_release(page);
> + return VM_FAULT_RETRY;
> + }
> + if (unlikely(page->mapping != mapping)) {
> + unlock_page(page);
> + page_cache_release(page);
> + goto repeat;
> + }
> + }
> +
> + error = get_block(inode, block, &bh, 0);
> + if (!error && (bh.b_size < PAGE_SIZE))
> + error = -EIO;
> + if (error)
> + goto unlock_page;
> +
> + if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
> + if (vmf->flags & FAULT_FLAG_WRITE) {
> + error = get_block(inode, block, &bh, 1);
> + count_vm_event(PGMAJFAULT);
> + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
> + major = VM_FAULT_MAJOR;
> + if (!error && (bh.b_size < PAGE_SIZE))
> + error = -EIO;
> + if (error)
> + goto unlock_page;
> + } else {
> + return dax_load_hole(mapping, page, vmf);
> + }
> + }
> +
> + if (vmf->cow_page) {
> + struct page *new_page = vmf->cow_page;
add newline.
> + if (buffer_written(&bh))
> + error = copy_user_bh(new_page, &bh, blkbits, vaddr);
> + else
> + clear_user_highpage(new_page, vaddr);
> + if (error)
> + goto unlock_page;
> + vmf->page = page;
> + if (!page) {
> + mutex_lock(&mapping->i_mmap_mutex);
> + /* Check we didn't race with truncate */
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >>
> + PAGE_SHIFT;
> + if (vmf->pgoff >= size) {
> + mutex_unlock(&mapping->i_mmap_mutex);
> + error = -EIO;
> + goto out;
> + }
> + }
If page is non-NULL, is it possible that we return VM_FAULT_LOCKED
without actually holding i_mmap_mutex ? Is it on purpose ?
> + return VM_FAULT_LOCKED;
> + }
Thanks,
Mathieu
> +
> + /* Check we didn't race with a read fault installing a new page */
> + if (!page && major)
> + page = find_lock_page(mapping, vmf->pgoff);
> +
> + if (page) {
> + unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
> + PAGE_CACHE_SIZE, 0);
> + delete_from_page_cache(page);
> + unlock_page(page);
> + page_cache_release(page);
> + }
> +
> + error = dax_insert_mapping(inode, &bh, vma, vmf);
> +
> + out:
> + if (error == -ENOMEM)
> + return VM_FAULT_OOM | major;
> + /* -EBUSY is fine, somebody else faulted on the same PTE */
> + if ((error < 0) && (error != -EBUSY))
> + return VM_FAULT_SIGBUS | major;
> + return VM_FAULT_NOPAGE | major;
> +
> + unlock_page:
> + if (page) {
> + unlock_page(page);
> + page_cache_release(page);
> + }
> + goto out;
> +}
> +
> +/**
> + * dax_fault - handle a page 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
> + * fault handler for DAX files.
> + */
> +int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> + get_block_t get_block)
> +{
> + int result;
> + struct super_block *sb = file_inode(vma->vm_file)->i_sb;
> +
> + if (vmf->flags & FAULT_FLAG_WRITE) {
> + sb_start_pagefault(sb);
> + file_update_time(vma->vm_file);
> + }
> + result = do_dax_fault(vma, vmf, get_block);
> + if (vmf->flags & FAULT_FLAG_WRITE)
> + sb_end_pagefault(sb);
> +
> + return result;
> +}
> +EXPORT_SYMBOL_GPL(dax_fault);
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index a247123..da8dc64 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -25,6 +25,37 @@
> #include "xattr.h"
> #include "acl.h"
>
> +#ifdef CONFIG_EXT2_FS_XIP
> +static int ext2_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + return dax_fault(vma, vmf, ext2_get_block);
> +}
> +
> +static int ext2_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + return dax_mkwrite(vma, vmf, ext2_get_block);
> +}
> +
> +static const struct vm_operations_struct ext2_dax_vm_ops = {
> + .fault = ext2_dax_fault,
> + .page_mkwrite = ext2_dax_mkwrite,
> + .remap_pages = generic_file_remap_pages,
> +};
> +
> +static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + if (!IS_DAX(file_inode(file)))
> + return generic_file_mmap(file, vma);
> +
> + file_accessed(file);
> + vma->vm_ops = &ext2_dax_vm_ops;
> + vma->vm_flags |= VM_MIXEDMAP;
> + return 0;
> +}
> +#else
> +#define ext2_file_mmap generic_file_mmap
> +#endif
> +
> /*
> * Called when filp is released. This happens when all file descriptors
> * for a single struct file are closed. Note that different open() calls
> @@ -70,7 +101,7 @@ const struct file_operations ext2_file_operations = {
> #ifdef CONFIG_COMPAT
> .compat_ioctl = ext2_compat_ioctl,
> #endif
> - .mmap = generic_file_mmap,
> + .mmap = ext2_file_mmap,
> .open = dquot_file_open,
> .release = ext2_release_file,
> .fsync = ext2_fsync,
> @@ -89,7 +120,7 @@ const struct file_operations ext2_xip_file_operations = {
> #ifdef CONFIG_COMPAT
> .compat_ioctl = ext2_compat_ioctl,
> #endif
> - .mmap = xip_file_mmap,
> + .mmap = ext2_file_mmap,
> .open = dquot_file_open,
> .release = ext2_release_file,
> .fsync = ext2_fsync,
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c04d371..338f04b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -49,6 +49,7 @@ struct swap_info_struct;
> struct seq_file;
> struct workqueue_struct;
> struct iov_iter;
> +struct vm_fault;
>
> extern void __init inode_init(void);
> extern void __init inode_init_early(void);
> @@ -2491,10 +2492,11 @@ extern int nonseekable_open(struct inode * inode, struct file * filp);
>
> #ifdef CONFIG_FS_XIP
> int dax_clear_blocks(struct inode *, sector_t block, long size);
> -extern int xip_file_mmap(struct file * file, struct vm_area_struct * vma);
> extern int xip_truncate_page(struct address_space *mapping, loff_t from);
> ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, struct iov_iter *,
> loff_t, get_block_t, dio_iodone_t, int flags);
> +int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
> +#define dax_mkwrite(vma, vmf, gb) dax_fault(vma, vmf, gb)
> #else
> static inline int dax_clear_blocks(struct inode *i, sector_t blk, long sz)
> {
> diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
> index f7c37a1..9dd45f3 100644
> --- a/mm/filemap_xip.c
> +++ b/mm/filemap_xip.c
> @@ -22,212 +22,6 @@
> #include <asm/io.h>
>
> /*
> - * We do use our own empty page to avoid interference with other users
> - * of ZERO_PAGE(), such as /dev/zero
> - */
> -static DEFINE_MUTEX(xip_sparse_mutex);
> -static seqcount_t xip_sparse_seq = SEQCNT_ZERO(xip_sparse_seq);
> -static struct page *__xip_sparse_page;
> -
> -/* called under xip_sparse_mutex */
> -static struct page *xip_sparse_page(void)
> -{
> - if (!__xip_sparse_page) {
> - struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> -
> - if (page)
> - __xip_sparse_page = page;
> - }
> - return __xip_sparse_page;
> -}
> -
> -/*
> - * __xip_unmap is invoked from xip_unmap and
> - * xip_write
> - *
> - * This function walks all vmas of the address_space and unmaps the
> - * __xip_sparse_page when found at pgoff.
> - */
> -static void
> -__xip_unmap (struct address_space * mapping,
> - unsigned long pgoff)
> -{
> - struct vm_area_struct *vma;
> - struct mm_struct *mm;
> - unsigned long address;
> - pte_t *pte;
> - pte_t pteval;
> - spinlock_t *ptl;
> - struct page *page;
> - unsigned count;
> - int locked = 0;
> -
> - count = read_seqcount_begin(&xip_sparse_seq);
> -
> - page = __xip_sparse_page;
> - if (!page)
> - return;
> -
> -retry:
> - mutex_lock(&mapping->i_mmap_mutex);
> - vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> - mm = vma->vm_mm;
> - address = vma->vm_start +
> - ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> - BUG_ON(address < vma->vm_start || address >= vma->vm_end);
> - pte = page_check_address(page, mm, address, &ptl, 1);
> - if (pte) {
> - /* Nuke the page table entry. */
> - flush_cache_page(vma, address, pte_pfn(*pte));
> - pteval = ptep_clear_flush(vma, address, pte);
> - page_remove_rmap(page);
> - dec_mm_counter(mm, MM_FILEPAGES);
> - BUG_ON(pte_dirty(pteval));
> - pte_unmap_unlock(pte, ptl);
> - /* must invalidate_page _before_ freeing the page */
> - mmu_notifier_invalidate_page(mm, address);
> - page_cache_release(page);
> - }
> - }
> - mutex_unlock(&mapping->i_mmap_mutex);
> -
> - if (locked) {
> - mutex_unlock(&xip_sparse_mutex);
> - } else if (read_seqcount_retry(&xip_sparse_seq, count)) {
> - mutex_lock(&xip_sparse_mutex);
> - locked = 1;
> - goto retry;
> - }
> -}
> -
> -/*
> - * xip_fault() is invoked via the vma operations vector for a
> - * mapped memory region to read in file data during a page fault.
> - *
> - * This function is derived from filemap_fault, but used for execute in place
> - */
> -static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> -{
> - struct file *file = vma->vm_file;
> - struct address_space *mapping = file->f_mapping;
> - struct inode *inode = mapping->host;
> - pgoff_t size;
> - void *xip_mem;
> - unsigned long xip_pfn;
> - struct page *page;
> - int error;
> -
> - /* XXX: are VM_FAULT_ codes OK? */
> -again:
> - size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
> - if (vmf->pgoff >= size)
> - return VM_FAULT_SIGBUS;
> -
> - error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
> - &xip_mem, &xip_pfn);
> - if (likely(!error))
> - goto found;
> - if (error != -ENODATA)
> - return VM_FAULT_OOM;
> -
> - /* sparse block */
> - if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
> - (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) &&
> - (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
> - int err;
> -
> - /* maybe shared writable, allocate new block */
> - mutex_lock(&xip_sparse_mutex);
> - error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
> - &xip_mem, &xip_pfn);
> - mutex_unlock(&xip_sparse_mutex);
> - if (error)
> - return VM_FAULT_SIGBUS;
> - /* unmap sparse mappings at pgoff from all other vmas */
> - __xip_unmap(mapping, vmf->pgoff);
> -
> -found:
> - /* We must recheck i_size under i_mmap_mutex */
> - mutex_lock(&mapping->i_mmap_mutex);
> - size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
> - PAGE_CACHE_SHIFT;
> - if (unlikely(vmf->pgoff >= size)) {
> - mutex_unlock(&mapping->i_mmap_mutex);
> - return VM_FAULT_SIGBUS;
> - }
> - err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
> - xip_pfn);
> - mutex_unlock(&mapping->i_mmap_mutex);
> - if (err == -ENOMEM)
> - return VM_FAULT_OOM;
> - /*
> - * err == -EBUSY is fine, we've raced against another thread
> - * that faulted-in the same page
> - */
> - if (err != -EBUSY)
> - BUG_ON(err);
> - return VM_FAULT_NOPAGE;
> - } else {
> - int err, ret = VM_FAULT_OOM;
> -
> - mutex_lock(&xip_sparse_mutex);
> - write_seqcount_begin(&xip_sparse_seq);
> - error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
> - &xip_mem, &xip_pfn);
> - if (unlikely(!error)) {
> - write_seqcount_end(&xip_sparse_seq);
> - mutex_unlock(&xip_sparse_mutex);
> - goto again;
> - }
> - if (error != -ENODATA)
> - goto out;
> -
> - /* We must recheck i_size under i_mmap_mutex */
> - mutex_lock(&mapping->i_mmap_mutex);
> - size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
> - PAGE_CACHE_SHIFT;
> - if (unlikely(vmf->pgoff >= size)) {
> - ret = VM_FAULT_SIGBUS;
> - goto unlock;
> - }
> - /* not shared and writable, use xip_sparse_page() */
> - page = xip_sparse_page();
> - if (!page)
> - goto unlock;
> - err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
> - page);
> - if (err == -ENOMEM)
> - goto unlock;
> -
> - ret = VM_FAULT_NOPAGE;
> -unlock:
> - mutex_unlock(&mapping->i_mmap_mutex);
> -out:
> - write_seqcount_end(&xip_sparse_seq);
> - mutex_unlock(&xip_sparse_mutex);
> -
> - return ret;
> - }
> -}
> -
> -static const struct vm_operations_struct xip_file_vm_ops = {
> - .fault = xip_file_fault,
> - .page_mkwrite = filemap_page_mkwrite,
> - .remap_pages = generic_file_remap_pages,
> -};
> -
> -int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
> -{
> - BUG_ON(!file->f_mapping->a_ops->get_xip_mem);
> -
> - file_accessed(file);
> - vma->vm_ops = &xip_file_vm_ops;
> - vma->vm_flags |= VM_MIXEDMAP;
> - return 0;
> -}
> -EXPORT_SYMBOL_GPL(xip_file_mmap);
> -
> -/*
> * truncate a page used for execute in place
> * functionality is analog to block_truncate_page but does use get_xip_mem
> * to get the page instead of page cache
> --
> 2.1.0
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxx. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
>
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
Key fingerprint: 2A0B 4ED9 15F2 D3FA 45F5 B162 1728 0A97 8118 6ACF
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>