On Fri, May 21, 2021 at 03:31:05PM +0800, Ming Lei wrote: > > iomap_ioend_bioset is sized to make sure we can always complete up > > to 4 pages, and the list is only used inside a page, so we're fine. > > The number itself does not matter, because there isn't any limit on how > many ioends can be allocated before submitting, for example, it can be > observed that 64 ioends is allocated before submitting when writing > 5GB file to ext4. So far the reserved pool size is 32. How do you manage to allocate iomap ioends when writing to ext4? ext4 doesn't use iomap for buffered I/O. > > fs_bio_set always has two entries to allow exactly for the common > > chain and submit pattern. > > It is easy to trigger dozens of chained bios in one ioend when writing > big file to XFS. Yes, we can still have one chained bio per ioend, so we need a bioset with the same size as iomap_ioend_bioset. That still should not be dozends for a common setup, though.
