On Tue, 12 Aug 2025 17:15:34 +0800, Jinliang Zheng wrote: > From: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx> > > With iomap_folio_state, we can identify uptodate states at the block > level, and a read_folio reading can correctly handle partially > uptodate folios. > > Therefore, when a partial write occurs, accept the block-aligned > partial write instead of rejecting the entire write. > > For example, suppose a folio is 2MB, blocksize is 4kB, and the copied > bytes are 2MB-3kB. > > Without this patchset, we'd need to recopy from the beginning of the > folio in the next iteration, which means 2MB-3kB of bytes is copy > duplicately. > > |<-------------------- 2MB -------------------->| > +-------+-------+-------+-------+-------+-------+ > | block | ... | block | block | ... | block | folio > +-------+-------+-------+-------+-------+-------+ > |<-4kB->| > > |<--------------- copied 2MB-3kB --------->| first time copied > |<-------- 1MB -------->| next time we need copy (chunk /= 2) > |<-------- 1MB -------->| next next time we need copy. > > |<------ 2MB-3kB bytes duplicate copy ---->| > > With this patchset, we can accept 2MB-4kB of bytes, which is block-aligned. > This means we only need to process the remaining 4kB in the next iteration, > which means there's only 1kB we need to copy duplicately. > > |<-------------------- 2MB -------------------->| > +-------+-------+-------+-------+-------+-------+ > | block | ... | block | block | ... | block | folio > +-------+-------+-------+-------+-------+-------+ > |<-4kB->| > > |<--------------- copied 2MB-3kB --------->| first time copied > |<-4kB->| next time we need copy > > |<>| > only 1kB bytes duplicate copy > > Although partial writes are inherently a relatively unusual situation and do > not account for a large proportion of performance testing, the optimization > here still makes sense in large-scale data centers. > > This patchset has been tested by xfstests' generic and xfs group, and > there's no new failed cases compared to the lastest upstream version kernel. Sorry forgot to cc Christoph Hellwig :) thanks, Jinliang Zheng > > Changelog: > > V3: patch[1]: use WARN_ON() instead of BUG_ON() > patch[2]: make commit message clear > patch[3]: - > patch[4]: make commit message clear > > V2: https://lore.kernel.org/linux-fsdevel/20250810101554.257060-1-alexjlzheng@xxxxxxxxxxx/ > use & instead of % for 64 bit variable on m68k/xtensa, try to make them happy: > m68k-linux-ld: fs/iomap/buffered-io.o: in function `iomap_adjust_read_range': > >> buffered-io.c:(.text+0xa8a): undefined reference to `__moddi3' > >> m68k-linux-ld: buffered-io.c:(.text+0xaa8): undefined reference to `__moddi3' > > V1: https://lore.kernel.org/linux-fsdevel/20250810044806.3433783-1-alexjlzheng@xxxxxxxxxxx/ > > Jinliang Zheng (4): > iomap: make sure iomap_adjust_read_range() are aligned with block_size > iomap: move iter revert case out of the unwritten branch > iomap: make iomap_write_end() return the number of written length > again > iomap: don't abandon the whole copy when we have iomap_folio_state > > fs/iomap/buffered-io.c | 68 +++++++++++++++++++++++++++++------------- > 1 file changed, 47 insertions(+), 21 deletions(-) > > -- > 2.49.0
