[PATCH 07/15] xfs: implement iomap based buffered write path

Christoph Hellwig
2016-05-09T08:47:59Z

Convert XFS to use the new iomap based multipage write path. This involves
implementing the ->iomap_begin and ->iomap_end methods, and switching the
buffered file write, page_mkwrite and xfs_iozero paths to the new iomap
helpers.

With this change __xfs_get_blocks will never be used for buffered writes,
and the code handling them can be removed.

Based on earlier code from Dave Chinner.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bob Peterson <rpeterso@redhat.com>
---
fs/xfs/Kconfig | 1 +
fs/xfs/xfs_aops.c | 212 -----------------------------------------------------
fs/xfs/xfs_file.c | 71 ++++++++----------
fs/xfs/xfs_iomap.c | 144 ++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_iomap.h | 5 +-
fs/xfs/xfs_iops.c | 9 ++-
fs/xfs/xfs_trace.h | 3 +
7 files changed, 187 insertions(+), 258 deletions(-)

diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
index 5d47b4d..35faf12 100644
--- a/fs/xfs/Kconfig
+++ b/fs/xfs/Kconfig
@@ -4,6 +4,7 @@ config XFS_FS
depends on (64BIT || LBDAF)
select EXPORTFS
select LIBCRC32C
+ select FS_IOMAP
help
XFS is a high performance journaling filesystem which originated
on the SGI IRIX platform. It is completely multi-threaded, can
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 40645a4..e481c80 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1429,216 +1429,6 @@ xfs_vm_direct_IO(
xfs_get_blocks_direct, endio, NULL, flags);
}

-/*
- * Punch out the delalloc blocks we have already allocated.
- *
- * Don't bother with xfs_setattr given that nothing can have made it to disk yet
- * as the page is still locked at this point.
- */
-STATIC void
-xfs_vm_kill_delalloc_range(
- struct inode *inode,
- loff_t start,
- loff_t end)
-{
- struct xfs_inode *ip = XFS_I(inode);
- xfs_fileoff_t start_fsb;
- xfs_fileoff_t end_fsb;
- int error;
-
- start_fsb = XFS_B_TO_FSB(ip->i_mount, start);
- end_fsb = XFS_B_TO_FSB(ip->i_mount, end);
- if (end_fsb <= start_fsb)
- return;
-
- xfs_ilock(ip, XFS_ILOCK_EXCL);
- error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
- end_fsb - start_fsb);
- if (error) {
- /* something screwed, just bail */
- if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
- xfs_alert(ip->i_mount,
- "xfs_vm_write_failed: unable to clean up ino %lld",
- ip->i_ino);
- }
- }
- xfs_iunlock(ip, XFS_ILOCK_EXCL);
-}
-
-STATIC void
-xfs_vm_write_failed(
- struct inode *inode,
- struct page *page,
- loff_t pos,
- unsigned len)
-{
- loff_t block_offset;
- loff_t block_start;
- loff_t block_end;
- loff_t from = pos & (PAGE_CACHE_SIZE - 1);
- loff_t to = from + len;
- struct buffer_head *bh, *head;
- struct xfs_mount *mp = XFS_I(inode)->i_mount;
-
- /*
- * The request pos offset might be 32 or 64 bit, this is all fine
- * on 64-bit platform. However, for 64-bit pos request on 32-bit
- * platform, the high 32-bit will be masked off if we evaluate the
- * block_offset via (pos & PAGE_MASK) because the PAGE_MASK is
- * 0xfffff000 as an unsigned long, hence the result is incorrect
- * which could cause the following ASSERT failed in most cases.
- * In order to avoid this, we can evaluate the block_offset of the
- * start of the page by using shifts rather than masks the mismatch
- * problem.
- */
- block_offset = (pos >> PAGE_CACHE_SHIFT) << PAGE_CACHE_SHIFT;
-
- ASSERT(block_offset + from == pos);
-
- head = page_buffers(page);
- block_start = 0;
- for (bh = head; bh != head || !block_start;
- bh = bh->b_this_page, block_start = block_end,
- block_offset += bh->b_size) {
- block_end = block_start + bh->b_size;
-
- /* skip buffers before the write */
- if (block_end <= from)
- continue;
-
- /* if the buffer is after the write, we're done */
- if (block_start >= to)
- break;
-
- /*
- * Process delalloc and unwritten buffers beyond EOF. We can
- * encounter unwritten buffers in the event that a file has
- * post-EOF unwritten extents and an extending write happens to
- * fail (e.g., an unaligned write that also involves a delalloc
- * to the same page).
- */
- if (!buffer_delay(bh) && !buffer_unwritten(bh))
- continue;
-
- if (!xfs_mp_fail_writes(mp) && !buffer_new(bh) &&
- block_offset < i_size_read(inode))
- continue;
-
- if (buffer_delay(bh))
- xfs_vm_kill_delalloc_range(inode, block_offset,
- block_offset + bh->b_size);
-
- /*
- * This buffer does not contain data anymore. make sure anyone
- * who finds it knows that for certain.
- */
- clear_buffer_delay(bh);
- clear_buffer_uptodate(bh);
- clear_buffer_mapped(bh);
- clear_buffer_new(bh);
- clear_buffer_dirty(bh);
- clear_buffer_unwritten(bh);
- }
-
-}
-
-/*
- * This used to call block_write_begin(), but it unlocks and releases the page
- * on error, and we need that page to be able to punch stale delalloc blocks out
- * on failure. hence we copy-n-waste it here and call xfs_vm_write_failed() at
- * the appropriate point.
- */
-STATIC int
-xfs_vm_write_begin(
- struct file *file,
- struct address_space *mapping,
- loff_t pos,
- unsigned len,
- unsigned flags,
- struct page **pagep,
- void **fsdata)
-{
- pgoff_t index = pos >> PAGE_CACHE_SHIFT;
- struct page *page;
- int status;
- struct xfs_mount *mp = XFS_I(mapping->host)->i_mount;
-
- ASSERT(len <= PAGE_CACHE_SIZE);
-
- page = grab_cache_page_write_begin(mapping, index, flags);
- if (!page)
- return -ENOMEM;
-
- status = __block_write_begin(page, pos, len, xfs_get_blocks);
- if (xfs_mp_fail_writes(mp))
- status = -EIO;
- if (unlikely(status)) {
- struct inode *inode = mapping->host;
- size_t isize = i_size_read(inode);
-
- xfs_vm_write_failed(inode, page, pos, len);
- unlock_page(page);
-
- /*
- * If the write is beyond EOF, we only want to kill blocks
- * allocated in this write, not blocks that were previously
- * written successfully.
- */
- if (xfs_mp_fail_writes(mp))
- isize = 0;
- if (pos + len > isize) {
- ssize_t start = max_t(ssize_t, pos, isize);
-
- truncate_pagecache_range(inode, start, pos + len);
- }
-
- page_cache_release(page);
- page = NULL;
- }
-
- *pagep = page;
- return status;
-}
-
-/*
- * On failure, we only need to kill delalloc blocks beyond EOF in the range of
- * this specific write because they will never be written. Previous writes
- * beyond EOF where block allocation succeeded do not need to be trashed, so
- * only new blocks from this write should be trashed. For blocks within
- * EOF, generic_write_end() zeros them so they are safe to leave alone and be
- * written with all the other valid data.
- */
-STATIC int
-xfs_vm_write_end(
- struct file *file,
- struct address_space *mapping,
- loff_t pos,
- unsigned len,
- unsigned copied,
- struct page *page,
- void *fsdata)
-{
- int ret;
-
- ASSERT(len <= PAGE_CACHE_SIZE);
-
- ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
- if (unlikely(ret < len)) {
- struct inode *inode = mapping->host;
- size_t isize = i_size_read(inode);
- loff_t to = pos + len;
-
- if (to > isize) {
- /* only kill blocks in this write beyond EOF */
- if (pos > isize)
- isize = pos;
- xfs_vm_kill_delalloc_range(inode, isize, to);
- truncate_pagecache_range(inode, isize, to);
- }
- }
- return ret;
-}
-
STATIC sector_t
xfs_vm_bmap(
struct address_space *mapping,
@@ -1749,8 +1539,6 @@ const struct address_space_operations xfs_address_space_operations = {
.set_page_dirty = xfs_vm_set_page_dirty,
.releasepage = xfs_vm_releasepage,
.invalidatepage = xfs_vm_invalidatepage,
- .write_begin = xfs_vm_write_begin,
- .write_end = xfs_vm_write_end,
.bmap = xfs_vm_bmap,
.direct_IO = xfs_vm_direct_IO,
.migratepage = buffer_migrate_page,
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 98bbd8f..bcedd80 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -37,6 +37,7 @@
#include "xfs_log.h"
#include "xfs_icache.h"
#include "xfs_pnfs.h"
+#include "xfs_iomap.h"

#include <linux/dcache.h>
#include <linux/falloc.h>
@@ -79,57 +80,27 @@ xfs_rw_ilock_demote(
inode_unlock(VFS_I(ip));
}

-/*
- * xfs_iozero clears the specified range supplied via the page cache (except in
- * the DAX case). Writes through the page cache will allocate blocks over holes,
- * though the callers usually map the holes first and avoid them. If a block is
- * not completely zeroed, then it will be read from disk before being partially
- * zeroed.
- *
- * In the DAX case, we can just directly write to the underlying pages. This
- * will not allocate blocks, but will avoid holes and unwritten extents and so
- * not do unnecessary work.
- */
-int
-xfs_iozero(
- struct xfs_inode *ip, /* inode */
- loff_t pos, /* offset in file */
- size_t count) /* size of data to zero */
+static int
+xfs_dax_zero_range(
+ struct inode *inode,
+ loff_t pos,
+ size_t count)
{
- struct page *page;
- struct address_space *mapping;
int status = 0;

-
- mapping = VFS_I(ip)->i_mapping;
do {
unsigned offset, bytes;
- void *fsdata;

offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
bytes = PAGE_CACHE_SIZE - offset;
if (bytes > count)
bytes = count;

- if (IS_DAX(VFS_I(ip))) {
- status = dax_zero_page_range(VFS_I(ip), pos, bytes,
- xfs_get_blocks_direct);
- if (status)
- break;
- } else {
- status = pagecache_write_begin(NULL, mapping, pos, bytes,
- AOP_FLAG_UNINTERRUPTIBLE,
- &page, &fsdata);
- if (status)
- break;
-
- zero_user(page, offset, bytes);
+ status = dax_zero_page_range(inode, pos, bytes,
+ xfs_get_blocks_direct);
+ if (status)
+ break;

- status = pagecache_write_end(NULL, mapping, pos, bytes,
- bytes, page, fsdata);
- WARN_ON(status <= 0); /* can't return less than zero! */
- status = 0;
- }
pos += bytes;
count -= bytes;
} while (count);
@@ -137,6 +108,24 @@ xfs_iozero(
return status;
}

+/*
+ * Clear the specified ranges to zero through either the pagecache or DAX.
+ * Holes and unwritten extents will be left as-is as they already are zeroed.
+ */
+int
+xfs_iozero(
+ struct xfs_inode *ip,
+ loff_t pos,
+ size_t count)
+{
+ struct inode *inode = VFS_I(ip);
+
+ if (IS_DAX(VFS_I(ip)))
+ return xfs_dax_zero_range(inode, pos, count);
+ else
+ return iomap_zero_range(inode, pos, count, NULL, &xfs_iomap_ops);
+}
+
int
xfs_update_prealloc_flags(
struct xfs_inode *ip,
@@ -842,7 +831,7 @@ xfs_file_buffered_aio_write(
write_retry:
trace_xfs_file_buffered_write(ip, iov_iter_count(from),
iocb->ki_pos, 0);
- ret = generic_perform_write(file, from, iocb->ki_pos);
+ ret = iomap_file_buffered_write(iocb, from, &xfs_iomap_ops);
if (likely(ret >= 0))
iocb->ki_pos += ret;

@@ -1558,7 +1547,7 @@ xfs_filemap_page_mkwrite(
if (IS_DAX(inode)) {
ret = __dax_mkwrite(vma, vmf, xfs_get_blocks_dax_fault, NULL);
} else {
- ret = block_page_mkwrite(vma, vmf, xfs_get_blocks);
+ ret = iomap_page_mkwrite(vma, vmf, &xfs_iomap_ops);
ret = block_page_mkwrite_return(ret);
}

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 2f37194..620fc91 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -967,3 +967,147 @@ xfs_bmbt_to_iomap(
iomap->length = XFS_FSB_TO_B(mp, imap->br_blockcount);
iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
}
+
+static inline bool imap_needs_alloc(struct xfs_bmbt_irec *imap, int nimaps)
+{
+ return !nimaps ||
+ imap->br_startblock == HOLESTARTBLOCK ||
+ imap->br_startblock == DELAYSTARTBLOCK;
+}
+
+static int
+xfs_file_iomap_begin(
+ struct inode *inode,
+ loff_t offset,
+ loff_t length,
+ unsigned flags,
+ struct iomap *iomap)
+{
+ struct xfs_inode *ip = XFS_I(inode);
+ struct xfs_mount *mp = ip->i_mount;
+ struct xfs_bmbt_irec imap;
+ xfs_fileoff_t offset_fsb, end_fsb;
+ int nimaps = 1, error = 0;
+
+ if (XFS_FORCED_SHUTDOWN(mp))
+ return -EIO;
+
+ xfs_ilock(ip, XFS_ILOCK_EXCL);
+
+ ASSERT(offset <= mp->m_super->s_maxbytes);
+ if ((xfs_fsize_t)offset + length > mp->m_super->s_maxbytes)
+ length = mp->m_super->s_maxbytes - offset;
+ offset_fsb = XFS_B_TO_FSBT(mp, offset);
+ end_fsb = XFS_B_TO_FSB(mp, offset + length);
+
+ error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
+ &nimaps, XFS_BMAPI_ENTIRE);
+ if (error) {
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ return error;
+ }
+
+ if ((flags & IOMAP_WRITE) && imap_needs_alloc(&imap, nimaps)) {
+ /*
+ * We cap the maximum length we map here to MAX_WRITEBACK_PAGES
+ * pages to keep the chunks of work done where somewhat symmetric
+ * with the work writeback does. This is a completely arbitrary
+ * number pulled out of thin air as a best guess for initial
+ * testing.
+ *
+ * Note that the values needs to be less than 32-bits wide until
+ * the lower level functions are updated.
+ */
+ length = min_t(loff_t, length, 1024 * PAGE_SIZE);
+ if (xfs_get_extsz_hint(ip)) {
+ /*
+ * xfs_iomap_write_direct() expects the shared lock. It
+ * is unlocked on return.
+ */
+ xfs_ilock_demote(ip, XFS_ILOCK_EXCL);
+ error = xfs_iomap_write_direct(ip, offset, length, &imap,
+ nimaps);
+ } else {
+ error = xfs_iomap_write_delay(ip, offset, length, &imap);
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ }
+
+ if (error)
+ return error;
+
+ trace_xfs_iomap_alloc(ip, offset, length, 0, &imap);
+ xfs_bmbt_to_iomap(ip, iomap, &imap);
+ } else if (nimaps) {
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ trace_xfs_iomap_found(ip, offset, length, 0, &imap);
+ xfs_bmbt_to_iomap(ip, iomap, &imap);
+ } else {
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ trace_xfs_iomap_not_found(ip, offset, length, 0, &imap);
+ iomap->blkno = IOMAP_NULL_BLOCK;
+ iomap->type = IOMAP_HOLE;
+ iomap->offset = offset;
+ iomap->length = length;
+ }
+
+ return 0;
+}
+
+static int
+xfs_file_iomap_end_delalloc(
+ struct xfs_inode *ip,
+ loff_t offset,
+ loff_t length,
+ ssize_t written)
+{
+ struct xfs_mount *mp = ip->i_mount;
+ xfs_fileoff_t start_fsb;
+ xfs_fileoff_t end_fsb;
+ int error = 0;
+
+ start_fsb = XFS_B_TO_FSB(mp, offset + written);
+ end_fsb = XFS_B_TO_FSB(mp, offset + length);
+
+ /*
+ * Trim back delalloc blocks if we didn't manage to write the whole
+ * range reserved.
+ *
+ * We don't need to care about racing delalloc as we hold i_mutex
+ * across the reserve/allocate/unreserve calls. If there are delalloc
+ * blocks in the range, they are ours.
+ */
+ if (start_fsb < end_fsb) {
+ xfs_ilock(ip, XFS_ILOCK_EXCL);
+ error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
+ end_fsb - start_fsb);
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+
+ if (error && !XFS_FORCED_SHUTDOWN(mp)) {
+ xfs_alert(mp, "%s: unable to clean up ino %lld",
+ __func__, ip->i_ino);
+ return error;
+ }
+ }
+
+ return 0;
+}
+
+static int
+xfs_file_iomap_end(
+ struct inode *inode,
+ loff_t offset,
+ loff_t length,
+ ssize_t written,
+ unsigned flags,
+ struct iomap *iomap)
+{
+ if ((flags & IOMAP_WRITE) && iomap->type == IOMAP_DELALLOC)
+ return xfs_file_iomap_end_delalloc(XFS_I(inode), offset,
+ length, written);
+ return 0;
+}
+
+struct iomap_ops xfs_iomap_ops = {
+ .iomap_begin = xfs_file_iomap_begin,
+ .iomap_end = xfs_file_iomap_end,
+};
diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
index 718f07c..e066d04 100644
--- a/fs/xfs/xfs_iomap.h
+++ b/fs/xfs/xfs_iomap.h
@@ -18,7 +18,8 @@
#ifndef __XFS_IOMAP_H__
#define __XFS_IOMAP_H__

-struct iomap;
+#include <linux/iomap.h>
+
struct xfs_inode;
struct xfs_bmbt_irec;

@@ -33,4 +34,6 @@ int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t);
void xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,
struct xfs_bmbt_irec *);

+extern struct iomap_ops xfs_iomap_ops;
+
#endif /* __XFS_IOMAP_H__*/
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 1a5ca4b..5d1fdae 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -38,6 +38,7 @@
#include "xfs_dir2.h"
#include "xfs_trans_space.h"
#include "xfs_pnfs.h"
+#include "xfs_iomap.h"

#include <linux/capability.h>
#include <linux/xattr.h>
@@ -822,8 +823,8 @@ xfs_setattr_size(
error = dax_truncate_page(inode, newsize,
xfs_get_blocks_direct);
} else {
- error = block_truncate_page(inode->i_mapping, newsize,
- xfs_get_blocks);
+ error = iomap_truncate_page(inode, newsize,
+ &did_zeroing, &xfs_iomap_ops);
}
}

@@ -838,8 +839,8 @@ xfs_setattr_size(
* problem. Note that this includes any block zeroing we did above;
* otherwise those blocks may not be zeroed after a crash.
*/
- if (newsize > ip->i_d.di_size &&
- (oldsize != ip->i_d.di_size || did_zeroing)) {
+ if (did_zeroing ||
+ (newsize > ip->i_d.di_size && oldsize != ip->i_d.di_size)) {
error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
ip->i_d.di_size, newsize);
if (error)
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 840d52e..86fb345 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -1296,6 +1296,9 @@ DEFINE_IOMAP_EVENT(xfs_map_blocks_alloc);
DEFINE_IOMAP_EVENT(xfs_get_blocks_found);
DEFINE_IOMAP_EVENT(xfs_get_blocks_alloc);
DEFINE_IOMAP_EVENT(xfs_get_blocks_map_direct);
+DEFINE_IOMAP_EVENT(xfs_iomap_alloc);
+DEFINE_IOMAP_EVENT(xfs_iomap_found);
+DEFINE_IOMAP_EVENT(xfs_iomap_not_found);

DECLARE_EVENT_CLASS(xfs_simple_io_class,
TP_PROTO(struct xfs_inode *ip, xfs_off_t offset, ssize_t count),