lkml.org 
[lkml]   [2011]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [GIT PULL] mm: frontswap (for 3.2 window)
On 11/01/2011 12:16 PM, James Bottomley wrote:
> Actually, I think there's an unexpressed fifth requirement:
>
> 5. The optimised use case should be for non-paging situations.
>
> The problem here is that almost every data centre person tries very hard
> to make sure their systems never tip into the swap zone. A lot of
> hosting datacentres use tons of cgroup controllers for this and
> deliberately never configure swap which makes transcendent memory
> useless to them under the current API. I'm not sure this is fixable,
> but it's the reason why a large swathe of users would never be
> interested in the patches, because they by design never operate in the
> region transcended memory is currently looking to address.
>
> This isn't an inherent design flaw, but it does ask the question "is
> your design scope too narrow?"

If you look at cleancache, then it addresses this concern - it extends
pagecache through host memory. When dropping a page from the tail of
the LRU it first goes into tmem, and when reading in a page from disk
you first try to read it from tmem. However in many workloads,
cleancache is actually detrimental. If you have a lot of cache misses,
then every one of them causes a pointless vmexit; considering that
servers today can chew hundreds of megabytes per second, this adds up.
On the other side, if you have a use-once workload, then every page that
falls of the tail of the LRU causes a vmexit and a pointless page copy.

--
error compiling committee.c: too many arguments to function



\
 
 \ /
  Last update: 2011-11-02 16:47    [W:0.132 / U:31.704 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site