On Thu, Oct 14, 2021 at 05:57:32PM -0400, Theodore Ts'o wrote: > On Fri, Oct 15, 2021 at 02:06:52AM +0800, Gao Xiang wrote: > > On Thu, Oct 14, 2021 at 12:54:14PM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote: > > > Hi, > > > > > > I'm seeing these i_reserved_data_blocks not cleared! messages when using ext4 > > > with nodelalloc, message added in: > > > > > > commit 6fed83957f21eff11c8496e9f24253b03d2bc1dc > > > Author: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> > > > Date: Mon Aug 23 14:13:58 2021 +0800 > > > > > > ext4: fix reserved space counter leakage > > > > > > I can quickly reproduce in 5.15.0-rc5-00041-g348949d9a444 by doing some > > > filesystem I/O while toggling delalloc: > > > > > > > > > while true; do mount -o remount,nodelalloc /; sleep 1; mount -o remount,delalloc /; sleep 1; done & > > > git clone linux xxx; rm -rf xxx > > > > If I understand correctly, switching such option implies > > sync inodes to write back exist delayed allocation blocks. > > Well, no. What it implies is that all writes after the remount into > an unallocated portion of the file will be allocated at the time when > the page is dirtied, instead of when the page is written back. It's > possible for some pages to be written using delayed allocation, and > some other pages in the legacy "allocate on page dirty" mechanism. > This can happen when the file system is remounted; it can also happen > when the file system starts getting close to 100% full. See the > comment in ext4_nonda_switch: > > /* > * switch to non delalloc mode if we are running low > * on free block. The free block accounting via percpu > * counters can get slightly wrong with percpu_counter_batch getting > * accumulated on each CPU without updating global counters > * Delalloc need an accurate free block accounting. So switch > * to non delalloc when we are near to error range. > */ Hi Ted, Ok, thanks for the detailed behavior explanation yet I guess several checks of "test_opt(inode->i_sb, DELALLOC)" could be somewhat racy then? For example a check in __es_remove_extent() of extents_status.c? Thanks, Gao Xiang > > Cheers, > > - Ted
