svn commit: r274673 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Xin Li]

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On 11/18/14 14:00, Slawa Olhovchenkov wrote:
> On Tue, Nov 18, 2014 at 06:40:02PM +0000, Xin LI wrote:
> 
>> Author: delphij Date: Tue Nov 18 18:40:01 2014 New Revision:
>> 274673 URL: https://svnweb.freebsd.org/changeset/base/274673
>> 
>> Log: Allow tuning zfs_max_recordsize via loader tunable.  Tuning
>> is NOT recommended.
> 
> This is not tuning, this is simple guard. And can be safe changed
> (incrased, at the least) in any time.

FWIW: It can be safely decreased: the ability to read such pool is
maintained.

> For some workload optimal is maximum, i.e. 16MB.
> 
> May be better comment: increasing this value required strong 
> understaning after-effects of increasing memory consumption and 
> bulk data transfers. (sorry for english)

That's true, but not free.  I don't think we have carefully evaluated
the situation (and possible mitigation measures, like, do we need to
make some improvements to the slab allocator?  It's never exposed to
workload like this before, etc.), and people tend to make uninformed
changes all the times (a lot of FreeBSD tuning guide gives wrong
instructions).

>> Requested by:	Slawa Olhovchenkov <slw zxy spb ru> MFC after:	2
>> weeks
> 
> Thanks, can you allow RW?

Sure, done in 274681.

I didn't do it at the beginning because I don't think it's a good idea
to make it easy for users to fiddle with it, and power users who
actually need to tweak do not change it often.  But you are right
there is no real technical reason not to allow read-write.

>> Modified: 
>> head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
>>
>>
>> 
Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
>> ==============================================================================
>>
>> 
- --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
Tue Nov 18 18:03:40 2014	(r274672)
>> +++
>> head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
>> Tue Nov 18 18:40:01 2014	(r274673) @@ -51,6 +51,8 @@ #include
>> <sys/dsl_userhold.h> #include <sys/dsl_bookmark.h>
>> 
>> +SYSCTL_DECL(_vfs_zfs); + /* * The SPA supports block sizes up to
>> 16MB.  However, very large blocks * can have an impact on i/o
>> latency (e.g. tying up a spinning disk for @@ -61,6 +63,9 @@ * of
>> this setting. */ int zfs_max_recordsize = 1 * 1024 * 1024; 
>> +SYSCTL_INT(_vfs_zfs, OID_AUTO, max_recordsize, CTLFLAG_RDTUN, +
>> &zfs_max_recordsize, 0, +    "Maximum block size.  Expect dragons
>> when tuning this.");
>> 
>> #define	SWITCH64(x, y) \ { \ 
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- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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