On Fri 20-02-15 17:15:51, Matthew Wilcox wrote:
> > So to handle this it can start transaction in ext4_dax_fault() /
> > ext4_dax_mkwrite() if write is requested and call ext4_jbd2_file_inode()
> > after dax_fault() / dax_mkwrite() returns. Complete function will look
> > something like follows:
>
> How about this? I tried to encompass both the unwritten extent conversion
> as well as starting the journal at the right point in the locking hierarchy.
>
> If we're going to expose do_dax_fault(), I think it needs to be called
> __dax_fault().
>
> I decided to return VM_FAULT_RETRY and a new flag VM_FAULT_UNWRITTEN from
> __dax_fault(), rather than convert it to return an errno.
I don't like using VM_FAULT_RETRY for ENOSPC. Different filesystems may
want different things on this condition. In particular, if a filesystem
decides to use dax_fault(), VM_FAULT_RETRY will get propagated up into mm
code which just retries the fault (or gets confused if FAULT_FLAG_ALLOW_RETRY
wasn't set).
If you want to stay with VM_FAULT_XXX return values (which makes some sense),
then I guess you need something like VM_FAULT_ENOSPC and convert that to
VM_FAULT_SIGBUS in dax_fault().
Otherwise the patch looks good.
Honza
> P.S. I love patches which touch *both* fs.h *and* mm.h. In case there
> were any files that weren't already being rebuilt.
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 556238f..81dbdaa 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -316,7 +316,7 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
> return error;
> }
>
> -static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> +int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> get_block_t get_block)
> {
> struct file *file = vma->vm_file;
> @@ -329,7 +329,7 @@ static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> sector_t block;
> pgoff_t size;
> int error;
> - int major = 0;
> + int ret = 0;
>
> size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> if (vmf->pgoff >= size)
> @@ -367,13 +367,15 @@ static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> error = -EIO; /* fs corruption? */
> if (error)
> goto unlock_page;
> + if (buffer_unwritten(&bh))
> + ret |= VM_FAULT_UNWRITTEN;
>
> 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;
> + ret = VM_FAULT_MAJOR;
> if (!error && (bh.b_size < PAGE_SIZE))
> error = -EIO;
> if (error)
> @@ -407,7 +409,7 @@ static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> }
>
> /* Check we didn't race with a read fault installing a new page */
> - if (!page && major)
> + if (!page && (ret & VM_FAULT_MAJOR))
> page = find_lock_page(mapping, vmf->pgoff);
>
> if (page) {
> @@ -421,12 +423,14 @@ static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> error = dax_insert_mapping(inode, &bh, vma, vmf);
>
> out:
> + if (error == -ENOSPC)
> + return VM_FAULT_RETRY | ret;
> if (error == -ENOMEM)
> - return VM_FAULT_OOM | major;
> + return VM_FAULT_OOM | ret;
> /* -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;
> + return VM_FAULT_SIGBUS | ret;
> + return VM_FAULT_NOPAGE | ret;
>
> unlock_page:
> if (page) {
> @@ -435,6 +439,7 @@ static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> }
> goto out;
> }
> +EXPORT_SYMBOL_GPL(__dax_fault);
>
> /**
> * dax_fault - handle a page fault on a DAX file
> @@ -455,7 +460,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> sb_start_pagefault(sb);
> file_update_time(vma->vm_file);
> }
> - result = do_dax_fault(vma, vmf, get_block);
> + result = __dax_fault(vma, vmf, get_block);
> if (vmf->flags & FAULT_FLAG_WRITE)
> sb_end_pagefault(sb);
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 4340e38..84b4f1c 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -194,7 +194,58 @@ errout:
> #ifdef CONFIG_FS_DAX
> static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> - return dax_fault(vma, vmf, ext4_get_block_write);
> + handle_t *handle;
> + int create = (vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page;
> + struct inode *inode = file_inode(vma->vm_file);
> + int ret, err = 0;
> + int retries = 0;
> +
> + if (create) {
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + retry_alloc:
> + handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
> + ext4_writepage_trans_blocks(inode));
> + if (IS_ERR(handle)) {
> + err = PTR_ERR(handle);
> + goto err;
> + }
> + }
> +
> + ret = __dax_fault(vma, vmf, ext4_get_block);
> +
> + if (create) {
> + if (ret & VM_FAULT_UNWRITTEN) {
> + loff_t offset = (loff_t)vmf->pgoff << PAGE_SHIFT;
> + err = ext4_convert_unwritten_extents(NULL, inode,
> + offset, PAGE_SIZE);
> + ret &= ~VM_FAULT_UNWRITTEN;
> + }
> + if (!err &&
> + ext4_test_inode_state(inode, EXT4_STATE_ORDERED_MODE))
> + err = ext4_jbd2_file_inode(handle, inode);
> +
> + if (err == -ENOSPC) {
> + ret |= VM_FAULT_RETRY;
> + err = 0;
> + }
> +
> + ext4_journal_stop(handle);
> + if (err < 0)
> + goto err;
> + if ((ret & VM_FAULT_RETRY) &&
> + ext4_should_retry_alloc(inode->i_sb, &retries))
> + goto retry_alloc;
> + ret &= ~VM_FAULT_RETRY;
> + }
> +
> + out:
> + if (create)
> + sb_end_pagefault(inode->i_sb);
> + return ret;
> + err:
> + ret = block_page_mkwrite_return(err);
> + goto out;
> }
>
> static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 85404f1..8f1ea7d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -657,18 +657,6 @@ has_zeroout:
> return retval;
> }
>
> -static void ext4_end_io_unwritten(struct buffer_head *bh, int uptodate)
> -{
> - struct inode *inode = bh->b_assoc_map->host;
> - /* XXX: breaks on 32-bit > 16GB. Is that even supported? */
> - loff_t offset = (loff_t)(uintptr_t)bh->b_private << inode->i_blkbits;
> - int err;
> - if (!uptodate)
> - return;
> - WARN_ON(!buffer_unwritten(bh));
> - err = ext4_convert_unwritten_extents(NULL, inode, offset, bh->b_size);
> -}
> -
> /* Maximum number of blocks we map for direct IO at once. */
> #define DIO_MAX_BLOCKS 4096
>
> @@ -706,11 +694,6 @@ static int _ext4_get_block(struct inode *inode, sector_t iblock,
>
> map_bh(bh, inode->i_sb, map.m_pblk);
> bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
> - if (IS_DAX(inode) && buffer_unwritten(bh) && !io_end) {
> - bh->b_assoc_map = inode->i_mapping;
> - bh->b_private = (void *)(unsigned long)iblock;
> - bh->b_end_io = ext4_end_io_unwritten;
> - }
> if (io_end && io_end->flag & EXT4_IO_END_UNWRITTEN)
> set_buffer_defer_completion(bh);
> bh->b_size = inode->i_sb->s_blocksize * map.m_len;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 239c89c..2af5050 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2597,6 +2597,7 @@ int dax_clear_blocks(struct inode *, sector_t block, long size);
> int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
> int dax_truncate_page(struct inode *, loff_t from, get_block_t);
> int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
> +int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
> int dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
> unsigned int flags, get_block_t);
> #define dax_mkwrite(vma, vmf, gb) dax_fault(vma, vmf, gb)
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ceb50ec..ffc9947 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1100,7 +1100,7 @@ static inline int page_mapped(struct page *page)
> #define VM_FAULT_HWPOISON 0x0010 /* Hit poisoned small page */
> #define VM_FAULT_HWPOISON_LARGE 0x0020 /* Hit poisoned large page. Index encoded in upper bits */
> #define VM_FAULT_SIGSEGV 0x0040
> -
> +#define VM_FAULT_UNWRITTEN 0x0080 /* Unwritten extent needs conversion */
> #define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page */
> #define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
> #define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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