svn commit: r287099 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Slawa Olhovchenkov]

On Mon, Aug 24, 2015 at 08:10:52AM +0000, Andriy Gapon wrote:

> Author: avg
> Date: Mon Aug 24 08:10:52 2015
> New Revision: 287099
> URL: https://svnweb.freebsd.org/changeset/base/287099
> 
> Log:
>   account for ashift when gathering buffers to be written to l2arc device
>   
>   The change that introduced the L2ARC compression support also introduced
>   a bug where the on-disk size of the selected buffers could end up larger
>   than the target size if the ashift is greater than 9.  This was because
>   the buffer selection could did not take into account the fact that
>   on-disk size could be larger than the in-memory buffer size due to
>   the alignment requirements.
>   
>   At the moment b_asize is a misnomer as it does not always represent the
>   allocated size: if a buffer is compressed, then the compressed size is
>   properly rounded (on FreeBSD), but if the compression fails or it is not
>   applied, then the original size is kept and it could be smaller than what
>   ashift requires.
>   
>   For the same reasons arcstat_l2_asize and the reported used space
>   on the cache device could be smaller than the actual allocated size
>   if ashift > 9.  That problem is not fixed by this change.
>   
>   This change only ensures that l2ad_hand is not advanced by more
>   than target_sz.  Otherwise we would overwrite active (unevicted)
>   L2ARC buffers.  That problem is manifested as growing l2_cksum_bad
>   and l2_io_error counters.
>   
>   This change also changes 'p' prefix to 'a' prefix in a few places
>   where variables represent allocated rather than physical size.
>   
>   The resolved problem could also result in the reported allocated size
>   being greater than the cache device's capacity, because of the
>   overwritten buffers (more than one buffer claiming the same disk
>   space).
>   
>   This change is already in ZFS-on-Linux:
>   zfsonlinux/zfs at ef56b0780c80ebb0b1e637b8b8c79530a8ab3201
>   
>   PR:		198242
>   PR:		195746 (possibly related)
>   Reviewed by:	mahrens (https://reviews.csiden.org/r/229/)
>   Tested by:	gkontos at aicom.gr (most recently)
>   MFC after:	15 days

Not ready?