On Thu, Oct 08, 2009 at 10:56:25AM -0500, Eric Sandeen wrote: > Aneesh Kumar K.V wrote: > > On Tue, Sep 29, 2009 at 11:47:19AM -0500, Eric Sandeen wrote: > >> I was running some of the xfstests enospc tests on ext4, and they were > >> failing; in one case, manymanymany small files are made to fill up a > >> 100M filesystem. ext4 stops quite early with -ENOSPC, but after a bit, > >> (or after a "sync") we get 40MB free again. So 40% of the fs space is > >> hidden somewhere in preallocation... > >> > >> I tried calling out to discard group prealloc but that's only a few > >> blocks. I'll go trace through the sync paths to see what all gets > >> released, but if anyone knows offhand where the rest of that space is > >> hiding, please give me a shout. :) > >> > > > > > > preallocation space is discarded by default if we fail a block allocation > > ext4_mb_discard_preallocations does that. What might be happening is the > > extra meta data blocks that we reserve for making sure we will be able > > to properly insert the new extent on block allocation. I guess we should > > force a data allocation when we fail with ENOSPC in ext4_da_writepages > > We currently force a journal commit so that the we claim back the blocks > > from deleted files. But we can also force block allocation for delayed > > allocated inodes so that we free some of the extra meta data we reserved > > > > -aneesh > > Yep, I should have followed up, I narrowed it down to just that - the > worst-case metadata blocks - 2 metadata blocks for a 20-byte write into > an empty file. :) > > I'm working on an inode walker to push out delalloc files on enospc. Should we do an inode walker ? I guess we should be doing something similar to balance_dirty_pages. That will kick in the flusher threads which inturn will force the block allocation of dirty inodes. -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
