Re: ReiserFS v3 choking when free space falls below 10%?

[Hans Reiser <reiser@namesys.com>]

Jan Kara wrote:

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>>Jan Kara wrote:
>>    
>>
>>>  Hi,
>>>
>>>  just one note: I've looked to the in scan_bitmap() in bitmap.c. There is:
>>>        /* When the bitmap is more than 10% free, anyone can allocate.
>>>         * When it's less than 10% free, only files that already use the
>>>         * bitmap are allowed. Once we pass 80% full, this restriction
>>>         * is lifted.
>>>         *
>>>         * We do this so that files that grow later still have space
>>>         * close to
>>>         * their original allocation. This improves locality, and
>>>         * presumably
>>>         * performance as a result.
>>>         *
>>>         * This is only an allocation policy and does not make up for
>>>         * getting a
>>>         * bad hint. Decent hinting must be implemented for this to work
>>>         * well.
>>>         */
>>>        if (TEST_OPTION(skip_busy, s)
>>>            && SB_FREE_BLOCKS(s) > SB_BLOCK_COUNT(s) / 20) {
>>>      
>>>
How about eliminating this feature entirely.   It seems rather dubious.

>>>   So the comment suggests we should lift the restriction when we are 80%
>>>full but if you see the condition, it checks wherher we are 95% full! I
>>>guess that is really asking for trouble and could explain the
>>>behaviour...
>>>  Mike could you try changing that 20 in the test to 5? IMHO that could
>>>fix your problem.
>>>      
>>>
>>Shoot. I guess I never sent that mail out last night. I had discovered
>>the same thing. The thing is, I don't think it will cause the kind of
>>performance problem we're seeing here. Once it sees the 90% check it
>>will bail out. Minor slowdown, not anything like we're seeing.
>>    
>>
>  Hmm, right. You'll only scan that one bitmap the file is in, won't
>  
>
I don't understand your remark.  These files are in many many
bitmaps....  Can you quote more of the code?

>you? That can still take some time so maybe it's worth trying this fix
>anyway.
>
>								Honza
>  
>