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SubjectRe: [PATCH 10/22] CacheFiles: Add a hook to write a single page of data to an inode
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On Fri, 2007-09-21 at 15:47 +0100, David Howells wrote:
> Add an address space operation to write one single page of data to an inode at
> a page-aligned location (thus permitting the implementation to be highly
> optimised).
>
> This is used by CacheFiles to store the contents of netfs pages into their
> backing file pages.
>
> Supply a generic implementation for this that uses the prepare_write() and
> commit_write() address_space operations to bound a copy directly into the page
> cache.
>
> Hook the Ext2 and Ext3 operations to the generic implementation.

So why do you need a new address space operation? AFAICS the generic
implementation will work for pretty much everyone who supports the
existing prepare_write()/commit_write().
Furthermore, you don't appear to supply any alternative "optimised"
implementations...

Trond


> Signed-Off-By: David Howells <dhowells@redhat.com>
> ---
>
> fs/ext2/inode.c | 2 +
> fs/ext3/inode.c | 3 ++
> include/linux/fs.h | 7 ++++
> mm/filemap.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 107 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 0079b2c..b3e4b50 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -695,6 +695,7 @@ const struct address_space_operations ext2_aops = {
> .direct_IO = ext2_direct_IO,
> .writepages = ext2_writepages,
> .migratepage = buffer_migrate_page,
> + .write_one_page = generic_file_buffered_write_one_page,
> };
>
> const struct address_space_operations ext2_aops_xip = {
> @@ -713,6 +714,7 @@ const struct address_space_operations ext2_nobh_aops = {
> .direct_IO = ext2_direct_IO,
> .writepages = ext2_writepages,
> .migratepage = buffer_migrate_page,
> + .write_one_page = generic_file_buffered_write_one_page,
> };
>
> /*
> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> index de4e316..93809eb 100644
> --- a/fs/ext3/inode.c
> +++ b/fs/ext3/inode.c
> @@ -1713,6 +1713,7 @@ static const struct address_space_operations ext3_ordered_aops = {
> .releasepage = ext3_releasepage,
> .direct_IO = ext3_direct_IO,
> .migratepage = buffer_migrate_page,
> + .write_one_page = generic_file_buffered_write_one_page,
> };
>
> static const struct address_space_operations ext3_writeback_aops = {
> @@ -1727,6 +1728,7 @@ static const struct address_space_operations ext3_writeback_aops = {
> .releasepage = ext3_releasepage,
> .direct_IO = ext3_direct_IO,
> .migratepage = buffer_migrate_page,
> + .write_one_page = generic_file_buffered_write_one_page,
> };
>
> static const struct address_space_operations ext3_journalled_aops = {
> @@ -1740,6 +1742,7 @@ static const struct address_space_operations ext3_journalled_aops = {
> .bmap = ext3_bmap,
> .invalidatepage = ext3_invalidatepage,
> .releasepage = ext3_releasepage,
> + .write_one_page = generic_file_buffered_write_one_page,
> };
>
> void ext3_set_aops(struct inode *inode)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bf35441..38f67ac 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -434,6 +434,11 @@ struct address_space_operations {
> int (*migratepage) (struct address_space *,
> struct page *, struct page *);
> int (*launder_page) (struct page *);
> + /* write the contents of the source page over the page at the specified
> + * index in the target address space (the source page does not need to
> + * be related to the target address space) */
> + int (*write_one_page)(struct address_space *, pgoff_t, struct page *);
> +
> };
>
> struct backing_dev_info;
> @@ -1669,6 +1674,8 @@ extern ssize_t generic_file_direct_write(struct kiocb *, const struct iovec *,
> unsigned long *, loff_t, loff_t *, size_t, size_t);
> extern ssize_t generic_file_buffered_write(struct kiocb *, const struct iovec *,
> unsigned long, loff_t, loff_t *, size_t, ssize_t);
> +extern int generic_file_buffered_write_one_page(struct address_space *,
> + pgoff_t, struct page *);
> extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
> extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
> extern void do_generic_mapping_read(struct address_space *mapping,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 3a61923..21aeee9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2016,6 +2016,101 @@ zero_length_segment:
> }
> EXPORT_SYMBOL(generic_file_buffered_write);
>
> +/**
> + * generic_file_buffered_write_one_page - Write a single page of data to an
> + * inode
> + * @mapping - The address space of the target inode
> + * @index - The target page in the target inode to fill
> + * @source - The data to write into the target page
> + *
> + * Write the data from the source page to the page in the nominated address
> + * space at the @index specified. Note that the file will not be extended if
> + * the page crosses the EOF marker, in which case only the first part of the
> + * page will be written.
> + *
> + * The @source page does not need to have any association with the file or the
> + * target page offset.
> + */
> +int generic_file_buffered_write_one_page(struct address_space *mapping,
> + pgoff_t index,
> + struct page *source)
> +{
> + const struct address_space_operations *a_ops = mapping->a_ops;
> + struct pagevec lru_pvec;
> + struct page *page, *cached_page = NULL;
> + unsigned psize;
> + loff_t isize;
> + long status = 0;
> +
> + pagevec_init(&lru_pvec, 0);
> +
> + page = __grab_cache_page(mapping, index, &cached_page, &lru_pvec);
> + if (!page) {
> + BUG_ON(cached_page);
> + return -ENOMEM;
> + }
> +
> + psize = PAGE_CACHE_SIZE;
> + isize = i_size_read(mapping->host);
> + if ((isize >> PAGE_SHIFT) == index)
> + psize = isize & (PAGE_SIZE - 1);
> +
> + status = a_ops->prepare_write(NULL, page, 0, psize);
> + if (unlikely(status)) {
> + isize = i_size_read(mapping->host);
> +
> + if (status != AOP_TRUNCATED_PAGE)
> + unlock_page(page);
> + page_cache_release(page);
> + if (status == AOP_TRUNCATED_PAGE)
> + goto sync;
> +
> + /* prepare_write() may have instantiated a few blocks outside
> + * i_size. Trim these off again.
> + */
> + if ((1ULL << (index + 1)) > isize)
> + vmtruncate(mapping->host, isize);
> + goto sync;
> + }
> +
> + copy_highpage(page, source);
> + flush_dcache_page(page);
> +
> + status = a_ops->commit_write(NULL, page, 0, psize);
> + if (status == AOP_TRUNCATED_PAGE) {
> + page_cache_release(page);
> + goto sync;
> + }
> +
> + if (status > 0)
> + status = 0;
> +
> + unlock_page(page);
> + mark_page_accessed(page);
> + page_cache_release(page);
> + if (status < 0)
> + return status;
> +
> + balance_dirty_pages_ratelimited(mapping);
> + cond_resched();
> +
> +sync:
> + if (cached_page)
> + page_cache_release(cached_page);
> +
> + /* the caller must handle O_SYNC themselves, but we handle S_SYNC and
> + * MS_SYNCHRONOUS here */
> + if (unlikely(IS_SYNC(mapping->host)) && !a_ops->writepage)
> + status = generic_osync_inode(mapping->host, mapping,
> + OSYNC_METADATA | OSYNC_DATA);
> +
> + /* the caller must handle O_DIRECT for themselves */
> +
> + pagevec_lru_add(&lru_pvec);
> + return status;
> +}
> +EXPORT_SYMBOL(generic_file_buffered_write_one_page);
> +
> static ssize_t
> __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
> unsigned long nr_segs, loff_t *ppos)
-
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