How ext2/ext3 tag metadata requests for I/O scheduler?

Question

In a paper i read ext2/ext3 filesystems tag all metadata requests(indirect blocks, ...) for I/O scheduler. but after a few hours reading ext2/3 source codes i couldn't find anything except REQ_META and REQ_PIRO which is just in ext3. i want to know is there anything else these two filesystems set to show a request is metadata request? after some testing i find out ext3 seems to don't tag indirect blocks.(reading 8000 random 4KB chunks from a 50GB file, just 2 requests with REQ_META). so is there anyhow else i can find out all metadata requests in I/O scheduler?

Answer 1

I suspect the use of metadata tags lead to ext3 filesystem corruption:

https://lkml.org/lkml/2010/7/23/87

So it is to be avoided. As indicated from above, and reading this:

http://www.kernel.org/doc/Documentation/filesystems/ext4.txt

to get a better understanding of "Metadata", it is possible to do away with it altogether, by always writing back to the main file (see this and look for explanation on "data=ordered").