linux-kernel - Re: [PATCH 2/3] xvmalloc memory allocator

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Date:	Sat, 21 Mar 2009 05:24:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nitin Gupta <nitingupta910@...il.com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, cl@...ux-foundation.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] xvmalloc memory allocator

On Sat, 21 Mar 2009 17:42:52 +0530 Nitin Gupta <nitingupta910@...il.com> wrote:

> Andrew Morton wrote:
> > On Sat, 21 Mar 2009 01:13:42 +0530 Nitin Gupta <ngupta@...are.org> wrote:
> 
> > But what is regrettable is that xvmalloc appears to be tied to
> > compressed-swap in some manner.  Is it not possible to split these two
> > initiatives apart so that neither is dependent upon the other?  Or is
> > compressed-swap hopelessly crippled without xvmalloc?
> 
> xvmalloc itself is completely independent of compressed-swap. Infact, its
> loaded as separate kernel module (xvmalloc.ko)

That sounds good.

> However, this compression project is almost useless without this specialized
> allocator.

Why?  Important information!!

See, being told all this helps us understand why xvmalloc exists.  Plus
once we have a good description of _why_ xvmalloc is needed, perhaps we can
come up with alternatives which are more palatable than merging a whole new
allocator.  Such as enhancing an existing one.

> > 
> > (compcache is a terrible name, btw - it isn't a "compressed cache" at all!)
> > 
> 
> I have now heard this many times and my conscious is beginning to hurt now :)
> I will change it to match name of its block device: ramzswap   sounds better?

Is there anything swap-specific about it?  It's a block device, yes?  I
should be able to run mkfs.ext2 on it and mount the thing?

> >> Anyways, I will move it to drivers/block.
> > 
> > This sounds like it might be a backward step.
> 
> 
> I'm bit confused here. Last thing I want to do is block mainline merge
> because of such issues. Its real pain to maintain these things separately.

This is why I tell myself to never use the word "it" in an email message.

I assumed that you were referring to moving xvmalloc() down into
drivers/block.  That would be bad, because then xvmalloc() will _never_ be
usable by anything other than ramzblock <new name!>?


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