On Tue, Aug 12, 2008 at 09:35:38AM -0700, Mingming Cao wrote: > Ext4: journal credit fix the delalloc writepages > > From: Mingming Cao <cmm@xxxxxxxxxx> > > Previous delalloc writepages implementation start a new transaction outside > a loop call of get_block() to do the block allocation. Due to lack of information > of how many blocks to be allocated, the estimate of the journal credits is very > Conservative and caused many issues. > > With the reworked delayed allocation, a new transaction is created for > each get_block(), thus we don't need to guess how many credits for the multiple > chunk of allocation. Start every transaction with credits for insert a single > extent is enough. But we still need to consider the journalled mode, where > it need to account for the number of data blocks. So we guess max number of > data blocks for each allocation. But we don't currently support data=journal with delalloc. > Due to the current VFS implementation > writepages() could only flush PAGEVEC of pages at a time, the max block > allocation is limited and calculated based on that, an the total number > of reserved delalloc datablocks, whichever is smaller. That is not correct. Currently write_cache_pages do while (!done && (index <= end) && (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, PAGECACHE_TAG_DIRTY, min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) { and mpage_da_submit_io does while (index <= end) { /* XXX: optimize tail */ nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE); ie we iterate till index > end. So we can very well have more than PAGEVEC number of pages in a single transaction. > > Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx> > --- > fs/ext4/inode.c | 39 ++++++++++++++++++++++++--------------- > 1 file changed, 24 insertions(+), 15 deletions(-) > > Index: linux-2.6.27-rc1/fs/ext4/inode.c > =================================================================== > --- linux-2.6.27-rc1.orig/fs/ext4/inode.c 2008-08-12 08:15:59.000000000 -0700 > +++ linux-2.6.27-rc1/fs/ext4/inode.c 2008-08-12 08:30:41.000000000 -0700 > @@ -2210,17 +2210,28 @@ static int ext4_da_writepage(struct page > } > > /* > - * 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 > + * This is called via ext4_da_writepages() to > + * calulate the total number of credits to reserve to fit > + * a single extent allocation into a single transaction, > + * ext4_da_writpeages() will loop calling this before > + * the block allocation. > + * > + * The page vector size limited the max number of pages could > + * be writeout at a time. Based on this, the max blocks to pass to > + * get_block is calculated > */ > -#define EXT4_MAX_WRITEBACK_PAGES DIO_MAX_BLOCKS > -#define EXT4_MAX_WRITEBACK_CREDITS 25 > + > +#define EXT4_MAX_WRITEPAGES_SIZE PAGEVEC_SIZE > +static int ext4_writepages_trans_blocks(struct inode *inode) > +{ > + int bpp = ext4_journal_blocks_per_page(inode); > + int max_blocks = EXT4_MAX_WRITEPAGES_SIZE * bpp; > + > + if (max_blocks > EXT4_I(inode)->i_reserved_data_blocks) > + max_blocks = EXT4_I(inode)->i_reserved_data_blocks; Why are we limiting max_blocks to i_reserved_data_blocks ? > + > + return ext4_data_trans_blocks(inode, max_blocks); > +} > > static int ext4_da_writepages(struct address_space *mapping, > struct writeback_control *wbc) > @@ -2262,7 +2273,7 @@ restart_loop: > * by delalloc > */ > BUG_ON(ext4_should_journal_data(inode)); > - needed_blocks = EXT4_DATA_TRANS_BLOCKS(inode->i_sb); > + needed_blocks = ext4_writepages_trans_blocks(inode); > The BUG_ON above is added to make sure we update this when start supporting data=journal mode with delalloc. > /* start a new transaction*/ > handle = ext4_journal_start(inode, needed_blocks); > @@ -4449,11 +4460,9 @@ static int ext4_writeblocks_trans_credit > * the modification of a single pages into a single transaction, > * which may include multile chunk of block allocations. > * > - * This could be called via ext4_write_begin() or later > - * ext4_da_writepages() in delalyed allocation case. > + * This could be called via ext4_write_begin() > * > - * In both case it's possible that we could allocating multiple > - * chunks of blocks. We need to consider the worse case, when > + * We need to consider the worse case, when > * one new block per extent. > */ > int ext4_writepage_trans_blocks(struct inode *inode) > > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html