Aneesh Kumar K.V wrote: > 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 it'll need to be synchronous to avoid a spurious enospc I think ... plus, we only want to flush delalloc inodes; flushing everythign would be needlessly expensive I think... need to think about the right way to do this. -Eric -- 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
