On Mon, May 08, 2023 at 12:57:59AM +0530, Ritesh Harjani (IBM) wrote: > Earlier when the folio is uptodate, we only allocate iop at writeback s/Earlier/Currently/ ? > time (in iomap_writepage_map()). This is ok until now, but when we are > going to add support for per-block dirty state bitmap in iop, this > could cause some performance degradation. The reason is that if we don't > allocate iop during ->write_begin(), then we will never mark the > necessary dirty bits in ->write_end() call. And we will have to mark all > the bits as dirty at the writeback time, that could cause the same write > amplification and performance problems as it is now. > > However, for all the writes with (pos, len) which completely overlaps > the given folio, there is no need to allocate an iop during > ->write_begin(). So skip those cases. This reads a bit backwards, I'd suggest to mention early allocation only happens for sub-page writes before going into the details. The changes themselves looks good to me.
