Re: [RFC] extents support for EXT3

[Ed Sweetman <ed.sweetman@wmich.edu>]

Alex Tomas wrote:
>>>>>>Ed Sweetman (ES) writes:
> 
> 
>  ES> I was testing this with only a single partition mounted with extents
>  ES> enabled when benchmarking.  Ext3 gave no messages of being mounted
>  ES> afterbootup with or without extents so to make sure i had extents
>  ES> enabled i booted with all my partitions with the extents option.  I
>  ES> suspect then my problems began.  I'm completely unaware of the extent
>  ES> of the damage enabling extents has done since most of the important
>  ES> things were opened, not created during my extents use.  In any case it
>  ES> may be that the reason why init is not able to be found is because i
>  ES> used apt and upgraded my system ...and I dont remember if i had
>  ES> extents enabled at the time or not.  If my init is in extents format
>  ES> though, then why is a patched kernel able to read it with extents not
>  ES> being enabled via the omunt option where as kernels without the patch
>  ES> cannot.  Is extents able to be read from a fs even when it's not
>  ES> mounted with the option but not written?   I'm kinda confused, this
>  ES> aspect of extents wasn't in the original email.
> 
> well, on my testbox I use _patched with extents_ ext3 as / and /boot partitions.
> I haven't seen any problems on them. with patch, ext3 look at special EXTENTS
> flag in inode (this flag is set up only for newly created files on fs being
> mounted with extents enabled) and calls apropriate routines. thus, it will
> call extents routines for those file even if fs is being mounted with extents
> disabled. I really do believe that your root filesystem haven't been mounted
> with extents enabled, so init must be stored in good old format.

Ok well little wait on the non-patched bootup.

I booted with test4-mm2 patched



Throughput 221.812 MB/sec 16 procs    ext2
Throughput 159.495 MB/sec 16 procs    ext3-extents (definitely enabled)
Throughput 147.598 MB/sec 16 procs    ext3 (patched but disabled)

There is an obvious improvement, but nothing near the 70+% increase you 
saw.  Subsequent runs run anything from a little lower than above for 
extents to 167MB/s.

I'm using the largest inode size possible for ext3 for the filesystem 
tested.


By the way, what's the behavior of opening an existing non-extent file 
and writing and reading to it while the partition is mounted with 
extents enabled?




>  ES> i'm going to try and boot a kernel without the extents patch (so far
>  ES> hasn't been possible) and run dbench again and see if i get different
>  ES> numbers.  I'm almost suspecting extents being enabled no matter what i
>  ES> mount the fs's as.
> 
> that would be fine!
> 
>