linux-kernel - Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 26 Apr 2010 09:06:13 +0300
From:	Avi Kivity <avi@...hat.com>
To:	ngupta@...are.org
CC:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hugh.dickins@...cali.co.uk, JBeulich@...ell.com,
	chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, npiggin@...e.de,
	akpm@...ux-foundation.org, riel@...hat.com
Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

On 04/25/2010 07:05 PM, Nitin Gupta wrote:
>
>>> Increasing the frequency of discards is also not an option:
>>>    - Creating discard bio requests themselves need memory and these
>>> swap devices
>>> come into picture only under low memory conditions.
>>>
>>>        
>> That's fine, swap works under low memory conditions by using reserves.
>>
>>      
> Ok, but still all this bio allocation and block layer overhead seems
> unnecessary and is easily avoidable. I think frontswap code needs
> clean up but at least it avoids all this bio overhead.
>    

Ok.  I agree it is silly to go through the block layer and end up 
servicing it within the kernel.

>>>    - We need to regularly scan swap_map to issue these discards.
>>> Increasing discard
>>> frequency also means more frequent scanning (which will still not be
>>> fast enough
>>> for ramzswap needs).
>>>
>>>        
>> How does frontswap do this?  Does it maintain its own data structures?
>>
>>      
> frontswap simply calls frontswap_flush_page() in swap_entry_free() i.e. as
> soon as a swap slot is freed. No bio allocation etc.
>    

The same code could also issue the discard?

>> Even for copying to RAM an async API is wanted, so you can dma it
>> instead of copying.
>>
>>      
> Maybe incremental development is better? Stabilize and refine existing
> code and gradually move to async API, if required in future?
>    

Incremental development is fine, especially for ramzswap where the APIs 
are all internal.  I'm more worried about external interfaces, these 
stick around a lot longer and if not done right they're a pain forever.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/