From: Bob Liu <lliubbo@gmail.com>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>,
Shaohua Li <shli@kernel.org>, Linux-MM <linux-mm@kvack.org>,
Bob Liu <bob.liu@oracle.com>,
Dan Magenheimer <dan.magenheimer@oracle.com>
Subject: Re: [RFC 0/4] cleancache: SSD backed cleancache backend
Date: Thu, 10 Oct 2013 18:38:46 +0800 [thread overview]
Message-ID: <CAA_GA1e79Uzj87hvN1fg9sp+u9BG2_UBwFy1EqU26WsPDeywWg@mail.gmail.com> (raw)
In-Reply-To: <20131009115243.GA1198@thunk.org>
On Wed, Oct 9, 2013 at 7:52 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> On Thu, Sep 26, 2013 at 11:14:01AM -0500, Seth Jennings wrote:
>>
>> I can see this burning out your SSD as well. If someone enabled this on
>> a machine that did large (relative to the size of the SDD) streaming
>> reads, you'd be writing to the SSD continuously and never have a cache
>> hit.
>
> If we are to do page-level caching, we really need to change the VM to
> use something like IBM's Adaptive Replacement Cache[1], which allows
> us to track which pages have been more frequently used, so that we
> only cache those pages, as opposed to those that land in the cache
> once and then aren't used again. (Consider what might happen if you
> are using clean cache and then the user does a full backup of the
> system.)
One way I used in zcache is adding a WasActive flag to page flags.
Only cache pages which are shrinked from active file lru list.
>
> [1] http://en.wikipedia.org/wiki/Adaptive_replacement_cache
>
> This is how ZFS does SSD caching; the basic idea is to only consider
> for cacheing those pages which have been promoted into its Frequenly
> Refrenced list, and then have been subsequently aged out. At that
> point, the benefit we would have over a dm-cache solution is that we
> would be taking advantage of the usage information tracked by the VM
> to better decide what is cached on the SSD.
>
> So something to think about,
>
--
Regards,
--Bob
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prev parent reply other threads:[~2013-10-10 10:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-26 14:14 Shaohua Li
2013-09-26 14:14 ` [RFC 1/4] cleancache: make put_page async possible Shaohua Li
2013-09-26 14:14 ` [RFC 2/4] cleancache: make get_page " Shaohua Li
2013-09-26 14:14 ` [RFC 3/4] cleancache: invalidate cache at dirty page Shaohua Li
2013-09-26 14:14 ` [RFC 4/4] cleancache: SSD backed cleancache backend Shaohua Li
2013-09-26 16:14 ` [RFC 0/4] " Seth Jennings
2013-09-29 9:19 ` Shaohua Li
2013-10-09 11:52 ` Theodore Ts'o
2013-10-10 10:24 ` Alex Elsayed
2013-10-10 10:38 ` Bob Liu [this message]
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