linux-kernel - Re: [v4 1/1] mm: Adaptive hash table scaling

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Date:   Sun, 21 May 2017 08:58:25 -0400
From:   Pasha Tatashin <pasha.tatashin@...cle.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...nel.org
Subject: Re: [v4 1/1] mm: Adaptive hash table scaling

Hi Andi,

Thank you for looking at this. I mentioned earlier, I would not want to 
impose a cap. However, if you think that for example dcache needs a cap, 
there is already a mechanism for that via high_limit argument, so the 
client can be changed to provide that cap. However, this particular 
patch addresses scaling problem for everyone by making it scale with 
memory at a slower pace.

Thank you,
Pasha

On 05/20/2017 10:07 PM, Andi Kleen wrote:
> Pavel Tatashin <pasha.tatashin@...cle.com> writes:
> 
>> Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT
>> is provided every time memory quadruples the sizes of hash tables will only
>> double instead of quadrupling as well. This algorithm starts working only
>> when memory size reaches a certain point, currently set to 64G.
>>
>> This is example of dentry hash table size, before and after four various
>> memory configurations:
> 
> IMHO the scale is still too aggressive. I find it very unlikely
> that a 1TB machine really needs 256MB of hash table because
> number of used files are unlikely to directly scale with memory.
> 
> Perhaps should just cap it at some large size, e.g. 32M
> 
> -Andi
> 
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