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Date: Wed, 09 May 2012 09:58:15 +0900
From: Minchan Kim <minchan@kernel.org>
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To: Dan Magenheimer <dan.magenheimer@oracle.com>
CC: Nitin Gupta <ngupta@vflare.org>, Pekka Enberg <penberg@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        Andrew Morton <akpm@linux-foundation.org>,
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        cl@linux-foundation.org
Subject: Re: [PATCH 4/4] zsmalloc: zsmalloc: align cache line size
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On 05/08/2012 11:00 PM, Dan Magenheimer wrote:

>> From: Minchan Kim [mailto:minchan@kernel.org]
>>> zcache can potentially create a lot of pools, so the latter will save
>>> some memory.
>>
>>
>> Dumb question.
>> Why should we create pool per user?
>> What's the problem if there is only one pool in system?
> 
> zcache doesn't use zsmalloc for cleancache pages today, but
> that's Seth's plan for the future.  Then if there is a
> separate pool for each cleancache pool, when a filesystem
> is umount'ed, it isn't necessary to walk through and delete
> all pages one-by-one, which could take quite awhile.

> 

> ramster needs one pool for each client (i.e. machine in the
> cluster) for frontswap pages for the same reason, and
> later, for cleancache pages, one per mounted filesystem
> per client


Fair enough.
But some subsystems can't want a own pool for not waste unnecessary memory.

Then, how about this interfaces like slab?

1. zs_handle zs_malloc(size_t size, gfp_t flags) - share a pool by many subsystem(like kmalloc)
2. zs_handle zs_malloc_pool(struct zs_pool *pool, size_t size) - use own pool(like kmem_cache_alloc)

Any thoughts?

> 
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-- 
Kind regards,
Minchan Kim
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