On Mon, 2009-03-30 at 16:53 +0530, Aneesh Kumar K.V wrote: > On Fri, Mar 27, 2009 at 05:30:52PM -0400, Theodore Tso wrote: > > On Fri, Mar 27, 2009 at 05:03:38PM -0400, Chris Mason wrote: > > > > Ric had asked me about a test program that would show the worst case > > > > ext3 behavior. So I've modified your ext3 program a little. It now > > > > creates a 8G file and forks off another proc to do random IO to that > > > > file. > > > > > > > > > > My understanding of ext4 delalloc is that once blocks are allocated to > > > file, we go back to data=ordered. > > > > Yes, that's correct. > > > > > Ext4 is going pretty slowly for this fsync test (slower than ext3), it > > > looks like we're going for a very long time in > > > jbd2_journal_commit_transaction -> write_cache_pages. > > > > One of the things that we can do to optimize this case for ext4 (and > > ext3) is that if block has already been written out to disk once, we > > don't have to flush it to disk a second time. So if we add a new > > buffer_head flag which can distinguish between blocks that have been > > newly allocated (and not yet been flushed to disk) versus blocks that > > have already been flushed to disk at least once, we wouldn't need to > > force I/O for blocks in the latter case. > > write_cache_pages should only look at pages which are marked dirty right > ?. So why are we writing these pages again and again ? The test program is constantly creating new dirty pages to random offsets on the disk ;) -chris -- 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
