Re: Question about memory pressure freezes

[Edward Shishkin <edward@namesys.com>]

Xu CanHao wrote:

>Hello!
>
>    Since the default atom_max_size is RAM/4, that means 256MB of
>maximum atom in your computer, and your HDD does 30MB/s which means
>you'll have 8s-9s "flush/system freeze" time.
>
>    IIRC, edward said the atom_max_size mount option is useless,
>

It is  useless for remount, in other cases it works fine
(for root file system it makes sense to edit fstab).
So you can pass the option "tmgr.atom_max_size=N",
where N  is atom size in blocks

> so
>I'd suggest you modify your reiser4/init_super.c and change:
>       sbinfo->tmgr.atom_max_size = totalram_pages / 4;
>to
>       sbinfo->tmgr.atom_max_size = totalram_pages / 16;
>which means your atom would have a maximum size of 64MB and a maximum
>freeze time of only 2 seconds.
>  
>

Such nice linear dependency disappears with some workload,
so freeze time is not comforting also for small atoms..

>Thanks!
>
>
>2007/7/28, Zan Lynx <zlynx@acm.org>:
>  
>
>>Edward answered my question mostly.
>>
>>But, I have 1 GB RAM and a Hitachi 7,200 RPM laptop drive.  It does
>>about 30 MB/s.
>>
>>On Fri, 2007-07-27 at 09:40 +0800, Xu CanHao wrote:
>>    
>>
>>>Hello!
>>>
>>>   How much is your RAM?
>>>   What is the result of your HDD's hdparm -t?
>>>
>>>Thanks!
>>>
>>>2007/7/27, Zan Lynx <zlynx@acm.org>:
>>>      
>>>
>>>>I have often experienced nearly full system freezes for up to five
>>>>seconds at a time while memory is being flushed to disk.
>>>>
>>>>I'm not sure if this is a general Linux problem or a Reiser4 problem, so
>>>>I thought I'd ask.
>>>>
>>>>A sysrq-T during the freeze shows many processes trying to acquire a
>>>>memory page, and Reiser4 flushing atoms and doing sync things.
>>>>
>>>>My working theory right now is that Reiser4 spends time flushing a lot
>>>>of data at once before returning.
>>>>
>>>>If I am right about that, would it not make more sense to flush a few
>>>>pages, return to the kernel, flush a few more pages, return to the
>>>>kernel, etc, etc?  That way programs could get a bit of RAM and make
>>>>some progress.
>>>>
>>>>Of course I could be completely off about what's going on.
>>>>--
>>>>Zan Lynx <zlynx@acm.org>
>>>>
>>>>
>>>>        
>>>>
>>--
>>Zan Lynx <zlynx@acm.org>
>>
>>
>>    
>>
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>  
>