--- Begin Message ---
- Subject: No Subject
- From:
- Date: Wed, 05 Jul 2006 20:45:18 +0400
From: Vladimir Saveliev <[email protected]>
This patch adds a method batch_write to struct address_space_operations.
A filesystem may want to implement this operation to improve write performance.
Generic implementation for the method is made by cut-n-paste off generic_file_buffered_write:
it writes one page using prepare_write and commit_write address space operations.
Signed-off-by: Vladimir Saveliev <[email protected]>
diff -puN include/linux/fs.h~batched-write include/linux/fs.h
--- linux-2.6.17-mm5/include/linux/fs.h~batched-write 2006-07-05 13:23:14.000000000 +0400
+++ linux-2.6.17-mm5-vs/include/linux/fs.h 2006-07-05 13:31:46.000000000 +0400
@@ -246,6 +246,7 @@ struct poll_table_struct;
struct kstatfs;
struct vm_area_struct;
struct vfsmount;
+struct pagevec;
extern void __init inode_init(unsigned long);
extern void __init inode_init_early(void);
@@ -347,6 +348,25 @@ struct page;
struct address_space;
struct writeback_control;
+/**
+ * struct write_descriptor - set of write arguments
+ * @pos: offset from the start of the file to write to
+ * @count: number of bytes to write
+ * @buf: pointer to data to be written
+ * @lru_pvec: multipage container to batch adding pages to LRU list
+ * @cached_page: allocated but not used on previous call
+ *
+ * This structure is to pass to batch_write file operation all
+ * information which is needed to continue write.
+ */
+struct write_descriptor {
+ loff_t pos;
+ size_t count;
+ char __user *buf;
+ struct page *cached_page;
+ struct pagevec *lru_pvec;
+};
+
struct address_space_operations {
int (*writepage)(struct page *page, struct writeback_control *wbc);
int (*readpage)(struct file *, struct page *);
@@ -367,6 +387,8 @@ struct address_space_operations {
*/
int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
+ long (*batch_write)(struct file *file, struct write_descriptor *desc,
+ size_t *written);
/* Unfortunately this kludge is needed for FIBMAP. Don't use it */
sector_t (*bmap)(struct address_space *, sector_t);
void (*invalidatepage) (struct page *, unsigned long);
diff -puN mm/filemap.c~batched-write mm/filemap.c
--- linux-2.6.17-mm5/mm/filemap.c~batched-write 2006-07-05 13:23:14.000000000 +0400
+++ linux-2.6.17-mm5-vs/mm/filemap.c 2006-07-05 13:47:58.000000000 +0400
@@ -2159,78 +2159,59 @@ generic_file_direct_write(struct kiocb *
}
EXPORT_SYMBOL(generic_file_direct_write);
-ssize_t
-generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
- unsigned long nr_segs, loff_t pos, loff_t *ppos,
- size_t count, ssize_t written)
+/**
+ * generic_batch_write - generic batch_write address space operation
+ * @file: the file to write to
+ * @desc: set of write arguments
+ * @written: returned number of bytes successfully written
+ *
+ * This implementation of batch_write address space operation writes not more
+ * than one page of file. It faults in user space, allocates page and calls
+ * prepare_write and commit_write address space operations. User data are
+ * copied by filemap_copy_from_user.
+ */
+static long generic_batch_write(struct file *file,
+ struct write_descriptor *desc,
+ size_t *written)
{
- struct file *file = iocb->ki_filp;
- struct address_space * mapping = file->f_mapping;
- const struct address_space_operations *a_ops = mapping->a_ops;
- struct inode *inode = mapping->host;
- long status = 0;
- struct page *page;
- struct page *cached_page = NULL;
- size_t bytes;
- struct pagevec lru_pvec;
- const struct iovec *cur_iov = iov; /* current iovec */
- size_t iov_base = 0; /* offset in the current iovec */
- char __user *buf;
-
- pagevec_init(&lru_pvec, 0);
-
- /*
- * handle partial DIO write. Adjust cur_iov if needed.
- */
- if (likely(nr_segs == 1))
- buf = iov->iov_base + written;
- else {
- filemap_set_next_iovec(&cur_iov, &iov_base, written);
- buf = cur_iov->iov_base + iov_base;
- }
-
- do {
- unsigned long index;
- unsigned long offset;
- size_t copied;
-
- offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
- index = pos >> PAGE_CACHE_SHIFT;
- bytes = PAGE_CACHE_SIZE - offset;
-
- /* Limit the size of the copy to the caller's write size */
- bytes = min(bytes, count);
-
- /*
- * Limit the size of the copy to that of the current segment,
- * because fault_in_pages_readable() doesn't know how to walk
- * segments.
- */
- bytes = min(bytes, cur_iov->iov_len - iov_base);
+ const struct address_space_operations *a_ops = file->f_mapping->a_ops;
+ struct page *page;
+ unsigned long index;
+ size_t bytes;
+ unsigned long offset;
+ long status;
+
+ /* offset within page write is to start at */
+ offset = (desc->pos & (PAGE_CACHE_SIZE - 1));
+
+ /* index of page we are to write to */
+ index = desc->pos >> PAGE_CACHE_SHIFT;
+
+ /* number of bytes which can be written to the page */
+ bytes = PAGE_CACHE_SIZE - offset;
+
+ /* limit the size of the copy to the caller's write size */
+ bytes = min(bytes, desc->count);
+ BUG_ON(bytes == 0);
+ while (1) {
/*
* Bring in the user page that we will copy from _first_.
- * Otherwise there's a nasty deadlock on copying from the
- * same page as we're writing to, without it being marked
+ * Otherwise there's a nasty deadlock on copying from the same
+ * page as we're writing to, without it being marked
* up-to-date.
*/
- fault_in_pages_readable(buf, bytes);
-
- page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
- if (!page) {
- status = -ENOMEM;
- break;
- }
+ fault_in_pages_readable(desc->buf, bytes);
- if (unlikely(bytes == 0)) {
- status = 0;
- copied = 0;
- goto zero_length_segment;
- }
+ page = __grab_cache_page(file->f_mapping, index,
+ &desc->cached_page, desc->lru_pvec);
+ if (!page)
+ return -ENOMEM;
- status = a_ops->prepare_write(file, page, offset, offset+bytes);
+ status = a_ops->prepare_write(file, page, offset,
+ offset+bytes);
if (unlikely(status)) {
- loff_t isize = i_size_read(inode);
+ loff_t isize = i_size_read(file->f_mapping->host);
if (status != AOP_TRUNCATED_PAGE)
unlock_page(page);
@@ -2241,58 +2222,120 @@ generic_file_buffered_write(struct kiocb
* prepare_write() may have instantiated a few blocks
* outside i_size. Trim these off again.
*/
- if (pos + bytes > isize)
- vmtruncate(inode, isize);
- break;
+ if (desc->pos + bytes > isize)
+ vmtruncate(file->f_mapping->host, isize);
+ return status;
}
- if (likely(nr_segs == 1))
- copied = filemap_copy_from_user(page, offset,
- buf, bytes);
- else
- copied = filemap_copy_from_user_iovec(page, offset,
- cur_iov, iov_base, bytes);
+
+ /* copy user data to the page */
+ *written = filemap_copy_from_user(page, offset, desc->buf,
+ bytes);
+
flush_dcache_page(page);
status = a_ops->commit_write(file, page, offset, offset+bytes);
if (status == AOP_TRUNCATED_PAGE) {
page_cache_release(page);
continue;
}
-zero_length_segment:
- if (likely(copied >= 0)) {
- if (!status)
- status = copied;
+ unlock_page(page);
+ mark_page_accessed(page);
+ page_cache_release(page);
+ break;
+ }
+ /*
+ * If commit_write returned error - write failed and we zero number of
+ * written bytes. If filemap_copy_from_user copied less than it was
+ * asked to we return -EFAULT and number of bytes actually written.
+ */
+ if (status)
+ *written = 0;
+ else if (*written != bytes)
+ status = -EFAULT;
+ return status;
+}
+
+ssize_t
+generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos, loff_t *ppos,
+ size_t count, ssize_t written)
+{
+ struct file *file = iocb->ki_filp;
+ struct address_space * mapping = file->f_mapping;
+ const struct address_space_operations *a_ops = mapping->a_ops;
+ struct inode *inode = mapping->host;
+ long status;
+ struct pagevec lru_pvec;
+ struct write_descriptor desc;
+ size_t copied = 0;
+ const struct iovec *cur_iov = iov; /* current iovec */
+ size_t iov_base = 0; /* offset in the current iovec */
+ long (*batch_write)(struct file *file,
+ struct write_descriptor *desc,
+ size_t *written);
- if (status >= 0) {
- written += status;
- count -= status;
- pos += status;
- buf += status;
- if (unlikely(nr_segs > 1)) {
+ pagevec_init(&lru_pvec, 0);
+
+ /*
+ * initialize write descriptor fields: position to write to
+ * and number of bytes to write
+ */
+ desc.pos = pos;
+ desc.cached_page = NULL;
+ desc.lru_pvec = &lru_pvec;
+
+ /*
+ * handle partial DIO write. Adjust cur_iov if needed.
+ */
+ if (likely(nr_segs == 1))
+ iov_base = written;
+ else
+ filemap_set_next_iovec(&cur_iov, &iov_base, written);
+
+ /*
+ * if file system implements batch_write method - use it, otherwise -
+ * use generic_batch_write
+ */
+ if (a_ops->batch_write)
+ batch_write = a_ops->batch_write;
+ else
+ batch_write = generic_batch_write;
+
+ do {
+ /* do not walk over current segment */
+ desc.buf = cur_iov->iov_base + iov_base;
+ desc.count = cur_iov->iov_len - iov_base;
+ if (desc.count > 0)
+ status = batch_write(file, &desc, &copied);
+ else {
+ copied = 0;
+ status = 0;
+ }
+ if (likely(copied >= 0)) {
+ written += copied;
+ count -= copied;
+ if (count) {
+ /*
+ * not everything is written yet. Adjust write
+ * descriptor for next iteration
+ */
+ desc.pos += copied;
+ if (likely(nr_segs == 1))
+ iov_base += copied;
+ else
filemap_set_next_iovec(&cur_iov,
- &iov_base, status);
- if (count)
- buf = cur_iov->iov_base +
- iov_base;
- } else {
- iov_base += status;
- }
+ &iov_base,
+ copied);
}
}
- if (unlikely(copied != bytes))
- if (status >= 0)
- status = -EFAULT;
- unlock_page(page);
- mark_page_accessed(page);
- page_cache_release(page);
- if (status < 0)
- break;
- balance_dirty_pages_ratelimited(mapping);
- cond_resched();
- } while (count);
- *ppos = pos;
-
- if (cached_page)
- page_cache_release(cached_page);
+ if (status < 0)
+ break;
+ balance_dirty_pages_ratelimited(mapping);
+ cond_resched();
+ } while (count);
+ *ppos = pos + written;
+
+ if (desc.cached_page)
+ page_cache_release(desc.cached_page);
/*
* For now, when the user asks for O_SYNC, we'll actually give O_DSYNC
diff -puN Documentation/filesystems/vfs.txt~batched-write Documentation/filesystems/vfs.txt
--- linux-2.6.17-mm5/Documentation/filesystems/vfs.txt~batched-write 2006-07-05 13:23:14.000000000 +0400
+++ linux-2.6.17-mm5-vs/Documentation/filesystems/vfs.txt 2006-07-05 19:36:15.000000000 +0400
@@ -534,6 +534,8 @@ struct address_space_operations {
struct list_head *pages, unsigned nr_pages);
int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
+ long (*batch_write)(struct file *file, struct write_descriptor *desc,
+ size_t *written);
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
@@ -624,6 +626,17 @@ struct address_space_operations {
operations. It should avoid returning an error if possible -
errors should have been handled by prepare_write.
+ batch_write: optional
+ When calling the filesystem for writes, there is processing
+ that must be done:
+ 1) per word
+ 2) per page
+ 3) per call to the FS
+ If the FS is called per page, then it turns out that 3) costs more
+ than 1) and 2) for sophisticated filesystems. To allow the FS to
+ choose to pay the cost of 3) only once we call batch_write, if the
+ FS supports it.
+
bmap: called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP
ioctl and for working with swap-files. To be able to swap to
_
--- End Message ---
