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Subject[PATCH 46/52] ext4: Invert lock ordering of page_lock and transaction start in delalloc
Date
From: Mingming Cao <cmm@us.ibm.com>

With the reverse locking, we need to start a transation before taking
the page lock, so in ext4_da_writepages() we need to break the write-out
into chunks, and restart the journal for each chunck to ensure the
write-out fits in a single transaction.

Updated patch from Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
which fixes delalloc sync hang with journal lock inversion, and address
the performance regression issue.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
fs/ext4/extents.c | 10 ++-
fs/ext4/inode.c | 189 +++++++++++++++++++++++++++++++++++++++--------------
fs/mpage.c | 12 ++--
3 files changed, 152 insertions(+), 59 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 88e08a3..f413be9 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2565,6 +2565,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
int err = 0, depth, ret;
unsigned long allocated = 0;
struct ext4_allocation_request ar;
+ loff_t disksize;

__clear_bit(BH_New, &bh_result->b_state);
ext_debug("blocks %u/%lu requested for inode %u\n",
@@ -2755,8 +2756,13 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
newblock = ext_pblock(&newex);
allocated = ext4_ext_get_actual_len(&newex);
outnew:
- if (extend_disksize && inode->i_size > EXT4_I(inode)->i_disksize)
- EXT4_I(inode)->i_disksize = inode->i_size;
+ if (extend_disksize) {
+ disksize = ((loff_t) iblock + ar.len) << inode->i_blkbits;
+ if (disksize > i_size_read(inode))
+ disksize = i_size_read(inode);
+ if (disksize > EXT4_I(inode)->i_disksize)
+ EXT4_I(inode)->i_disksize = disksize;
+ }

set_buffer_new(bh_result);

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4545542..db5aee8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -846,6 +846,7 @@ int ext4_get_blocks_handle(handle_t *handle, struct inode *inode,
struct ext4_inode_info *ei = EXT4_I(inode);
int count = 0;
ext4_fsblk_t first_block = 0;
+ loff_t disksize;


J_ASSERT(!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL));
@@ -921,8 +922,13 @@ int ext4_get_blocks_handle(handle_t *handle, struct inode *inode,
* protect it if you're about to implement concurrent
* ext4_get_block() -bzzz
*/
- if (!err && extend_disksize && inode->i_size > ei->i_disksize)
- ei->i_disksize = inode->i_size;
+ if (!err && extend_disksize) {
+ disksize = ((loff_t) iblock + count) << inode->i_blkbits;
+ if (disksize > i_size_read(inode))
+ disksize = i_size_read(inode);
+ if (disksize > ei->i_disksize)
+ ei->i_disksize = disksize;
+ }
if (err)
goto cleanup;

@@ -1580,18 +1586,14 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
{
- int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
+ int ret;
unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
loff_t disksize = EXT4_I(inode)->i_disksize;
handle_t *handle = NULL;

- if (create) {
- handle = ext4_journal_start(inode, needed_blocks);
- if (IS_ERR(handle)) {
- ret = PTR_ERR(handle);
- goto out;
- }
- }
+ handle = ext4_journal_current_handle();
+ BUG_ON(handle == NULL);
+ BUG_ON(create == 0);

ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
bh_result, create, 0, EXT4_DELALLOC_RSVED);
@@ -1620,65 +1622,157 @@ static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
up_write(&EXT4_I(inode)->i_data_sem);

if (EXT4_I(inode)->i_disksize == disksize) {
- if (handle == NULL)
- handle = ext4_journal_start(inode, 1);
- if (!IS_ERR(handle))
- ext4_mark_inode_dirty(handle, inode);
+ ret = ext4_mark_inode_dirty(handle, inode);
+ return ret;
}
}
-
ret = 0;
}
-
-out:
- if (handle && !IS_ERR(handle))
- ext4_journal_stop(handle);
-
return ret;
}
+
+static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
+{
+ return !buffer_mapped(bh) || buffer_delay(bh);
+}
+
/* FIXME!! only support data=writeback mode */
+/*
+ * get called vi ext4_da_writepages after taking page lock
+ * We may end up doing block allocation here in case
+ * mpage_da_map_blocks failed to allocate blocks.
+ */
static int ext4_da_writepage(struct page *page,
struct writeback_control *wbc)
{
- struct inode *inode = page->mapping->host;
- handle_t *handle = NULL;
int ret = 0;
- int err;
+ loff_t size;
+ unsigned long len;
+ handle_t *handle = NULL;
+ struct buffer_head *page_bufs;
+ struct inode *inode = page->mapping->host;

- if (ext4_journal_current_handle())
- goto out_fail;
+ handle = ext4_journal_current_handle();
+ if (!handle) {
+ /*
+ * This can happen when we aren't called via
+ * ext4_da_writepages() but directly (shrink_page_list).
+ * We cannot easily start a transaction here so we just skip
+ * writing the page in case we would have to do so.
+ */
+ size = i_size_read(inode);

- handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
- if (IS_ERR(handle)) {
- ret = PTR_ERR(handle);
- goto out_fail;
+ page_bufs = page_buffers(page);
+ if (page->index == size >> PAGE_CACHE_SHIFT)
+ len = size & ~PAGE_CACHE_MASK;
+ else
+ len = PAGE_CACHE_SIZE;
+
+ if (walk_page_buffers(NULL, page_bufs, 0,
+ len, NULL, ext4_bh_unmapped_or_delay)) {
+ /*
+ * We can't do block allocation under
+ * page lock without a handle . So redirty
+ * the page and return
+ */
+ BUG_ON(wbc->sync_mode != WB_SYNC_NONE);
+ redirty_page_for_writepage(wbc, page);
+ unlock_page(page);
+ return 0;
+ }
}

if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
- ret = nobh_writepage(page, ext4_get_block, wbc);
+ ret = nobh_writepage(page, ext4_da_get_block_write, wbc);
else
- ret = block_write_full_page(page, ext4_get_block, wbc);
+ ret = block_write_full_page(page, ext4_da_get_block_write, wbc);

- if (!ret && inode->i_size > EXT4_I(inode)->i_disksize) {
- EXT4_I(inode)->i_disksize = inode->i_size;
- ext4_mark_inode_dirty(handle, inode);
- }
-
- err = ext4_journal_stop(handle);
- if (!ret)
- ret = err;
- return ret;
-
-out_fail:
- redirty_page_for_writepage(wbc, page);
- unlock_page(page);
return ret;
}

+
+/*
+ * For now just follow the DIO way to estimate the max credits
+ * needed to write out EXT4_MAX_WRITEBACK_PAGES.
+ * todo: need to calculate the max credits need for
+ * extent based files, currently the DIO credits is based on
+ * indirect-blocks mapping way.
+ *
+ * Probably should have a generic way to calculate credits
+ * for DIO, writepages, and truncate
+ */
+#define EXT4_MAX_WRITEBACK_PAGES DIO_MAX_BLOCKS
+#define EXT4_MAX_WRITEBACK_CREDITS DIO_CREDITS
+
static int ext4_da_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
- return mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+ struct inode *inode = mapping->host;
+ handle_t *handle = NULL;
+ int needed_blocks;
+ int ret = 0;
+ long to_write;
+ loff_t range_start = 0;
+
+ /*
+ * No pages to write? This is mainly a kludge to avoid starting
+ * a transaction for special inodes like journal inode on last iput()
+ * because that could violate lock ordering on umount
+ */
+ if (!mapping->nrpages)
+ return 0;
+
+ /*
+ * Estimate the worse case needed credits to write out
+ * EXT4_MAX_BUF_BLOCKS pages
+ */
+ needed_blocks = EXT4_MAX_WRITEBACK_CREDITS;
+
+ to_write = wbc->nr_to_write;
+ if (!wbc->range_cyclic) {
+ /*
+ * If range_cyclic is not set force range_cont
+ * and save the old writeback_index
+ */
+ wbc->range_cont = 1;
+ range_start = wbc->range_start;
+ }
+
+ while (!ret && to_write) {
+ /* start a new transaction*/
+ handle = ext4_journal_start(inode, needed_blocks);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ goto out_writepages;
+ }
+ /*
+ * set the max dirty pages could be write at a time
+ * to fit into the reserved transaction credits
+ */
+ if (wbc->nr_to_write > EXT4_MAX_WRITEBACK_PAGES)
+ wbc->nr_to_write = EXT4_MAX_WRITEBACK_PAGES;
+
+ to_write -= wbc->nr_to_write;
+ ret = mpage_da_writepages(mapping, wbc,
+ ext4_da_get_block_write);
+ ext4_journal_stop(handle);
+ if (wbc->nr_to_write) {
+ /*
+ * There is no more writeout needed
+ * or we requested for a noblocking writeout
+ * and we found the device congested
+ */
+ to_write += wbc->nr_to_write;
+ break;
+ }
+ wbc->nr_to_write = to_write;
+ }
+
+out_writepages:
+ wbc->nr_to_write = to_write;
+ if (range_start)
+ wbc->range_start = range_start;
+ return ret;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
@@ -1728,11 +1822,6 @@ out:
return ret;
}

-static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
-{
- return !buffer_mapped(bh) || buffer_delay(bh);
-}
-
static int ext4_da_write_end(struct file *file,
struct address_space *mapping,
loff_t pos, unsigned len, unsigned copied,
diff --git a/fs/mpage.c b/fs/mpage.c
index cde7f11..c4376ec 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -849,13 +849,11 @@ static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
do {
if (cur_logical >= logical + blocks)
break;
-
if (buffer_delay(bh)) {
bh->b_blocknr = pblock;
clear_buffer_delay(bh);
- } else if (buffer_mapped(bh)) {
+ } else if (buffer_mapped(bh))
BUG_ON(bh->b_blocknr != pblock);
- }

cur_logical++;
pblock++;
@@ -930,10 +928,10 @@ static void mpage_da_map_blocks(struct mpage_da_data *mpd)
if (buffer_delay(lbh))
mpage_put_bnr_to_bhs(mpd, next, &new);

- /* go for the remaining blocks */
- next += new.b_size >> mpd->inode->i_blkbits;
- remain -= new.b_size;
- }
+ /* go for the remaining blocks */
+ next += new.b_size >> mpd->inode->i_blkbits;
+ remain -= new.b_size;
+ }
}

#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | (1 << BH_Delay))
--
1.5.6.rc3.1.g36b7.dirty


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