Hi all,
I've recently started looking into killing off the ->writepage method,
and as an initial subproject kill of external uses of generic_writepages.
One of the two remaining callers s in jbd2 and I'm a bit confused about
it.
jbd2_journal_submit_inode_data_buffers has two comments that explicitly
ask for ->writepages as that doesn't allocate data:
/*
* write the filemap data using writepage() address_space_operations.
* We don't do block allocation here even for delalloc. We don't
* use writepages() because with delayed allocation we may be doing
* block allocation in writepages().
*/
/*
* submit the inode data buffers. We use writepage
* instead of writepages. Because writepages can do
* block allocation with delalloc. We need to write
* only allocated blocks here.
*/
and these look really stange to me. ->writepage and ->writepages per
their document VM/VFS semantics don't different on what they allocate,
so this seems to reverse engineer ext4 internal behavior in some
way. Either way looping over ->writepage just for that is rather
inefficient. If jbd2 really wants a way to skip delalloc conversion
can we come up with a flag in struct writeback_control for that?
Is there anyone familiar enough with this code who would be willing
to give it a try?
