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Date:	Thu, 21 Aug 2008 23:01:21 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	"Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger@....com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: ENOSPC returned during writepages

On Thu, Aug 21, 2008 at 10:07:37AM -0700, Mingming Cao wrote:
> 
> 在 2008-08-21四的 22:15 +0530,Aneesh Kumar K.V写道:
> > On Wed, Aug 20, 2008 at 11:13:39AM +0530, Aneesh Kumar K.V wrote:
> > > Hi,
> > > 
> > > I am getting this even with the latest patch queue. The test program is
> > > a modified fsstress with fallocate support.
> > > 
> > > mpage_da_map_blocks block allocation failed for inode 377954 at logical
> > > offset 313 with max blocks 4 with error -28
> > > mpage_da_map_blocks block allocation failed for inode 336367 at logical
> > > offset 74 with max blocks 9 with error -28
> > > mpage_da_map_blocks block allocation failed for inode 345560 at logical
> > > offset 542 with max blocks 7 with error -28
> > > This should not happen.!! Data will be lost
> > > mpage_da_map_blocks block allocation failed for inode 355317 at logical
> > > offset 152 with max blocks 10 with error -28
> > > This should not happen.!! Data will be lost
> > > mpage_da_map_blocks block allocation failed for inode 395261 at logical
> > > offset 462 with max blocks 1 with error -28
> > > This should not happen.!! Data will be lost
> > > mpage_da_map_blocks block allocation failed for inode 323784 at logical
> > > offset 313 with max blocks 11 with error -28
> > > This should not happen.!! Data will be lost
> > > 
> > 
> > With this patch i am not seeing error. It does the below
> > 
> > a) use ext4_claim_free_blocks that also update the free blocks count
> > b) Later after block allocation update the free blocks count if we
> > allocated less with non-delayed mode
> > c) Switch to non delay mode if we are low on free blocks. 
> > 
> I had sent a patch to do c) yesterday, I noticed that we can't switch to
> non delayed mode if the inode already have some delalloc dirty pages.
> 
> 
> > @@ -2462,11 +2464,21 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
> >  	unsigned from, to;
> >  	struct inode *inode = mapping->host;
> >  	handle_t *handle;
> > +	s64 free_blocks;
> > +	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> > 
> >  	index = pos >> PAGE_CACHE_SHIFT;
> >  	from = pos & (PAGE_CACHE_SIZE - 1);
> >  	to = from + len;
> > 
> > +	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
> > +	if (free_blocks < (4 * (FBC_BATCH * nr_cpu_ids))) {
> > +		/* switch to non delalloc mode */
> > +		*fsdata = (void *)1;
> > +		return ext4_write_begin(file, mapping, pos,
> > +					len, flags, pagep, fsdata);
> > +	}
> > +	*fsdata = (void *)0;
> 
> No, calling ext4_write_begin() directly won't work, as it start a
> handle, do the block allocation , and leave the handle there.   It
> expect later the write_end aops  to file the inode to the transaction
> list, and close that handle. 
> 
> With your change, the aops write_end still points to the
> ext4_da_write_end(), which doesn't match the ext4_write_begin. We need
> to switch the aop write_begin/write_end  function pointers all together.
> 

My patch does it in a simple way. I am attaching only switch to non
delalloc patch below. It is still being tested.

commit 490b69bd47b9ea27b1bb86bbdfb85a2911047149
Author: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Date:   Thu Aug 21 22:10:50 2008 +0530

    switch to non-delalloc

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d965a05..087abca 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1030,11 +1030,17 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
 	BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
 	mdb_free = EXT4_I(inode)->i_reserved_meta_blocks - mdb;
 
-	/* Account for allocated meta_blocks */
-	mdb_free -= EXT4_I(inode)->i_allocated_meta_blocks;
+	if (mdb_free) {
+		/* Account for allocated meta_blocks */
+		mdb_free -= EXT4_I(inode)->i_allocated_meta_blocks;
 
-	/* update fs free blocks counter for truncate case */
-	percpu_counter_add(&sbi->s_freeblocks_counter, mdb_free);
+		/*
+		 * We have reserved more blocks.
+		 * Now free the extra blocks reserved
+		 */
+		percpu_counter_add(&sbi->s_freeblocks_counter, mdb_free);
+		EXT4_I(inode)->i_allocated_meta_blocks = 0;
+	}
 
 	/* update per-inode reservations */
 	BUG_ON(used  > EXT4_I(inode)->i_reserved_data_blocks);
@@ -1042,7 +1048,6 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
 
 	BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
 	EXT4_I(inode)->i_reserved_meta_blocks = mdb;
-	EXT4_I(inode)->i_allocated_meta_blocks = 0;
 	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 }
 
@@ -2459,11 +2464,21 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 	unsigned from, to;
 	struct inode *inode = mapping->host;
 	handle_t *handle;
+	s64 free_blocks;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
 	index = pos >> PAGE_CACHE_SHIFT;
 	from = pos & (PAGE_CACHE_SIZE - 1);
 	to = from + len;
 
+	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
+	if (free_blocks < (4 * (FBC_BATCH * nr_cpu_ids))) {
+		/* switch to non delalloc mode */
+		*fsdata = (void *)1;
+		return ext4_write_begin(file, mapping, pos,
+					len, flags, pagep, fsdata);
+	}
+	*fsdata = (void *)0;
 retry:
 	/*
 	 * With delayed allocation, we don't log the i_disksize update
@@ -2532,6 +2547,19 @@ static int ext4_da_write_end(struct file *file,
 	handle_t *handle = ext4_journal_current_handle();
 	loff_t new_i_size;
 	unsigned long start, end;
+	int low_free_blocks = (int)fsdata;
+
+	if (low_free_blocks) {
+		if (ext4_should_order_data(inode)) {
+			return ext4_ordered_write_end(file, mapping, pos,
+					len, copied, page, fsdata);
+		} else if (ext4_should_writeback_data(inode)) {
+			return ext4_writeback_write_end(file, mapping, pos,
+					len, copied, page, fsdata);
+		} else {
+			BUG();
+		}
+	}
 
 	start = pos & (PAGE_CACHE_SIZE - 1);
 	end = start + copied -1;
--
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