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Date: Mon, 13 Oct 2008 00:31:43 +0400
From: Dmitri Monakhov <dmonakhov@...nvz.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: cmm@...ibm.com, tytso@....edu, sandeen@...hat.com, npiggin@...e.de,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] ext4: Fix file fragmentation during large file write.
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
> The range_cyclic writeback mode uses the address_space writeback_index
> as the start index for writeback. With delayed allocation we were
> updating writeback_index wrongly resulting in highly fragmented file.
> Number of extents reduced from 4000 to 27 for a 3GB file with the below
> patch.
Hi i've played with fragmentation patches with following result:
I've had several crash and deadlocks
for example objects wasn't freed on umount:
EXT4-fs: mballoc: 12800 blocks 13 reqs (6 success)
EXT4-fs: mballoc: 7 extents scanned, 12 goal hits, 1 2^N hits, 0 breaks, 0 lost
EXT4-fs: mballoc: 1 generated and it took 3024
EXT4-fs: mballoc: 7608 preallocated, 1536 discarded
slab error in kmem_cache_destroy(): cache `ext4_prealloc_space': Can't free all objects
Pid: 7703, comm: rmmod Not tainted 2.6.27-rc8 #3
Call Trace:
[<ffffffff8028b011>] kmem_cache_destroy+0x7d/0xc0
[<ffffffffa03ca057>] exit_ext4_mballoc+0x10/0x1e [ext4dev]
[<ffffffffa03d35b3>] exit_ext4_fs+0x1f/0x2f [ext4dev]
[<ffffffff80250dff>] sys_delete_module+0x199/0x1f3
[<ffffffff8025d06e>] audit_syscall_entry+0x12d/0x160
[<ffffffff8020be0b>] system_call_fastpath+0x16/0x1b
Some times sync has stuck.
I'm not shure is it because of current patch set, but where is at least one
brand new bug. See later.
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> ---
> fs/ext4/inode.c | 83 +++++++++++++++++++++++++++++++++----------------------
> 1 files changed, 50 insertions(+), 33 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index cba7960..844c136 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1648,6 +1648,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
> int ret = 0, err, nr_pages, i;
> unsigned long index, end;
> struct pagevec pvec;
> + long pages_skipped;
>
> BUG_ON(mpd->next_page <= mpd->first_page);
> pagevec_init(&pvec, 0);
> @@ -1655,7 +1656,6 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
> end = mpd->next_page - 1;
[1] In fact mpd->next_page may be bigger whan (index + wbc->nr_to_write)
this result in incorrect math while exit from mpage_da_writepages()
Probably we have bound end_index here.
end = min(mpd->next_page, index +wbc->nr_to_write) -1;
>
> while (index <= end) {
> - /* XXX: optimize tail */
> /*
> * We can use PAGECACHE_TAG_DIRTY lookup here because
> * even though we have cleared the dirty flag on the page
> @@ -1673,8 +1673,13 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
> for (i = 0; i < nr_pages; i++) {
> struct page *page = pvec.pages[i];
>
> + pages_skipped = mpd->wbc->pages_skipped;
> err = mapping->a_ops->writepage(page, mpd->wbc);
> - if (!err)
> + if (!err && (pages_skipped == mpd->wbc->pages_skipped))
> + /*
> + * have successfully written the page
> + * without skipping the same
> + */
> mpd->pages_written++;
> /*
> * In error case, we have to continue because
> @@ -2110,7 +2115,6 @@ static int mpage_da_writepages(struct address_space *mapping,
> struct writeback_control *wbc,
> struct mpage_da_data *mpd)
> {
> - long to_write;
> int ret;
>
> if (!mpd->get_block)
> @@ -2125,10 +2129,7 @@ static int mpage_da_writepages(struct address_space *mapping,
> mpd->pages_written = 0;
> mpd->retval = 0;
>
> - to_write = wbc->nr_to_write;
> -
> ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, mpd);
> -
> /*
> * Handle last extent of pages
> */
> @@ -2137,7 +2138,7 @@ static int mpage_da_writepages(struct address_space *mapping,
> mpage_da_submit_io(mpd);
> }
>
> - wbc->nr_to_write = to_write - mpd->pages_written;
> + wbc->nr_to_write -= mpd->pages_written;
due to [1] wbc->nr_write becomes negative here
> return ret;
> }
>
> @@ -2366,11 +2367,14 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
> static int ext4_da_writepages(struct address_space *mapping,
> struct writeback_control *wbc)
> {
> + pgoff_t index;
> + int range_whole = 0;
> handle_t *handle = NULL;
> + long pages_written = 0;
> struct mpage_da_data mpd;
> struct inode *inode = mapping->host;
> + int no_nrwrite_update, no_index_update;
> int needed_blocks, ret = 0, nr_to_writebump = 0;
> - long to_write, pages_skipped = 0;
> struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
>
> /*
> @@ -2390,16 +2394,27 @@ static int ext4_da_writepages(struct address_space *mapping,
> nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;
> wbc->nr_to_write = sbi->s_mb_stream_request;
> }
> + if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
> + range_whole = 1;
>
> -
> - pages_skipped = wbc->pages_skipped;
> + if (wbc->range_cyclic)
> + index = mapping->writeback_index;
> + else
> + index = wbc->range_start >> PAGE_CACHE_SHIFT;
>
> mpd.wbc = wbc;
> mpd.inode = mapping->host;
>
> -restart_loop:
> - to_write = wbc->nr_to_write;
> - while (!ret && to_write > 0) {
> + /*
> + * we don't want write_cache_pages to update
> + * nr_to_write and writeback_index
> + */
> + no_nrwrite_update = wbc->no_nrwrite_update;
> + wbc->no_nrwrite_update = 1;
> + no_index_update = wbc->no_index_update;
> + wbc->no_index_update = 1;
> +
> + while (!ret && wbc->nr_to_write > 0) {
>
> /*
> * we insert one extent at a time. So we need
> @@ -2420,46 +2435,48 @@ static int ext4_da_writepages(struct address_space *mapping,
> dump_stack();
> goto out_writepages;
> }
> - to_write -= wbc->nr_to_write;
> -
> mpd.get_block = ext4_da_get_block_write;
> ret = mpage_da_writepages(mapping, wbc, &mpd);
>
> ext4_journal_stop(handle);
>
> - if (mpd.retval == -ENOSPC)
> + if (mpd.retval == -ENOSPC) {
> + /* commit the transaction which would
> + * free blocks released in the transaction
> + * and try again
> + */
> jbd2_journal_force_commit_nested(sbi->s_journal);
> -
> - /* reset the retry count */
> - if (ret == MPAGE_DA_EXTENT_TAIL) {
> + ret = 0;
> + } else if (ret == MPAGE_DA_EXTENT_TAIL) {
> /*
> * got one extent now try with
> * rest of the pages
> */
> - to_write += wbc->nr_to_write;
> + pages_written += mpd.pages_written;
> ret = 0;
> - } else if (wbc->nr_to_write) {
> + } else 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;
> - }
> -
> - if (!wbc->range_cyclic && (pages_skipped != wbc->pages_skipped)) {
> - /* We skipped pages in this loop */
> - wbc->nr_to_write = to_write +
> - wbc->pages_skipped - pages_skipped;
> - wbc->pages_skipped = pages_skipped;
> - goto restart_loop;
> }
> + /* Update index */
> + index += pages_written;
> + if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
> + /*
> + * set the writeback_index so that range_cyclic
> + * mode will write it back later
> + */
> + mapping->writeback_index = index;
>
> out_writepages:
> - wbc->nr_to_write = to_write - nr_to_writebump;
> + if (!no_nrwrite_update)
> + wbc->no_nrwrite_update = 0;
> + if (!no_index_update)
> + wbc->no_index_update = 0;
> + wbc->nr_to_write -= nr_to_writebump;
> return ret;
> }
BTW: please add following cleanup fix.
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6efa4ca..c248cbc 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2603,7 +2603,7 @@ 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 write_mode = (int)fsdata;
+ int write_mode = (int)(unsigned long)fsdata;
if (write_mode == FALL_BACK_TO_NONDELALLOC) {
if (ext4_should_order_data(inode)) {
--
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