On Tue, 2007-11-06 at 00:15 +0800, Andreas Dilger wrote: > On Nov 05, 2007 08:04 -0800, Badari Pulavarty wrote: > > On Sat, 2007-11-03 at 09:36 +0800, Andreas Dilger wrote: > > > But... this implies that every user of bh->b_data needs to kmap, and I > > > don't see that in the code anywhere else. That makes me think something > > > else is going wrong here. > > > > Most cases, this is handled in ll_rw_block() code - when we submit the > > buffer head for IO. If the page is in highmem, we will end up creating > > a bounce bufer for it. > > > > In our case, JBD code is trying to look at the data to do checksum > > on it. Thats why we have to kmap() the page before looking. > > My point is that there is a LOT of code in ext[234] that dereferences > bh->b_data without kmap() (e.g. group descriptors, bitmaps, superblock, > inode tables, etc). Does that imply that something is forcing those > bh pages into lowmem, or is the journal bh page in question being > allocated in some different way that allows it to be in highmem? Yes. You are right. Its been a while since I had to deal with HIGHMEM. All the meta-data should be in LOWMEM. I asked Mingming to verify what the buffer-head is pointing to when it has HIGHMEM page. Thanks, Badari - 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
