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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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      Last update: 2007-09-21 21:33    [W:0.037 / U:101.308 seconds]
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