Re: ENOSPC returned during writepages

Aneesh Kumar K.V
2008-08-21T17:31:43Z

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@linux.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;