On 2011年08月17日 11:25, Darrick J. Wong Wrote: > Hi all, > > I've created a page on the ext4 wiki outlining the patchset that I'm working on > to add metadata checksumming to ext4. The page can be found at this address: > https://ext4.wiki.kernel.org/index.php/Ext4_Metadata_Checksums > Hi Darrick, I just go through the proposal, have on objection for most of the text. Only some things want to confirm, 1) If a metadata_csum enabled file system is metadata_csum disabled, it should be better to mark the block group or inode whether the existing (disabled) checksum is valid or not. So if people re-enable metadata_csum, we can save quite a lot of time to re-build check sums for all metadata objects. 2) In no-journal mode, every time when we modify the metadata objects, we may have to hold a lock, calculate the check sum, and release the lock, which may introduce performance regression. I hope this is only my unnecessary over worry. BTW, an engineer in Taobao kernel team, is trying to count different meta data objects I/O in run time now. One of the first efforts, is trying to unify a set of routines to read or dirty meta data object blocks. A.k.a something (might) like ext4_read_ext_block(), ext4_read_idx_block(), ... etc. Then the counting routines can be added inside the meta data object blocks I/O routines. So far, it seems the modification is not trivial, needs more study on the code. Anyway, since you mentioned on the wiki page, just let you know what we are doing now :-) P.S. The idea of meta data I/O counting is to help us understanding the I/O characteristic of our online servers running Ext4 file systems, which is the basic material for further I/O performance optimization. Thanks. -- Coly Li -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
