On Tue, 2009-09-15 at 00:22 +0530, Aneesh Kumar K.V wrote: > On Mon, Sep 14, 2009 at 07:50:56PM +0200, Jan Kara wrote: > > I've found some time to look into this and I can see a few problems in > > the code. Firstly, what may cause your problems: > > vfs_dq_claim_blocks() is called in ext4_mb_mark_diskspace_used(). But > > as far as I can understand the code, ext4_mb_normalize_request() can > > increase the amount of space we really allocate and thus we try to > > allocate more blocks than we have actually reserved in quota. Aneesh, is > > that right? > > ext4_mb_mark_diskspace_used use ac->ac_b_ex.fe_len which is NOT the normalized > request len. it is min(allocated_len, original_len). So i guess that code > should be safe > That's right. ac->ac_b_ex.fe_len is the number of blocks that account for the original request. It is used for update the per-fs free blocks counter and the per-fs dirty(delayed) blocks counter too. Quota counters are updated based on this value. > > > Secondly, ext4_da_reserve_space() seems to have a bug that it can reserve > > quota blocks multiple times if ext4_claim_free_blocks() fail and we retry > > the allocation. We should release the quota reservation before restarting. > > Actually, when we find out we cannot reserve quota space, we could force > > some delayed allocated writes to disk (thus possibly release some quota > > in case we have overestimated the amount of blocks needed). But that's > > a different issue. > > That would imply the file system was full. But the dumpe2fs ouput list > large number of free blocks. But yes the code should have released the > quota reservation before trying block reservation again. > > I'll send out a patch shortly. > > Thirdly, ext4_indirect_calc_metadata_amount() is wrong for sparse files. > > The worst case is 3 metadata blocks per data block if we make the file > > sufficiently sparse and there's no easy way around that... > > > If this is a real concern, I am all for fix it. Just we have consider the worse case before, at that time it seems a little overprotect that we have always account for the worse case. In regularly cases, we pretty much always reserve more metadata(indirect) blocks than needed... > -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 -- 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
