From: Shaohua Li <shli@kernel.org>
To: Kyungmin Park <kmpark@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>,
lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org,
Rik van Riel <riel@redhat.com>,
Simon Jeons <simon.jeons@gmail.com>
Subject: Re: [LSF/MM TOPIC]swap improvements for fast SSD
Date: Sun, 27 Jan 2013 22:18:53 +0800 [thread overview]
Message-ID: <20130127141853.GB27019@kernel.org> (raw)
In-Reply-To: <CAH9JG2UpVtxeLB21kx5-_pokK8p_uVZ-2o41Ep--oOyKStBZFQ@mail.gmail.com>
On Sat, Jan 26, 2013 at 01:40:55PM +0900, Kyungmin Park wrote:
> Hi,
>
> On 1/24/13, Simon Jeons <simon.jeons@gmail.com> wrote:
> > Hi Minchan,
> > On Wed, 2013-01-23 at 16:58 +0900, Minchan Kim wrote:
> >> On Tue, Jan 22, 2013 at 02:53:41PM +0800, Shaohua Li wrote:
> >> > Hi,
> >> >
> >> > Because of high density, low power and low price, flash storage (SSD) is
> >> > a good
> >> > candidate to partially replace DRAM. A quick answer for this is using
> >> > SSD as
> >> > swap. But Linux swap is designed for slow hard disk storage. There are a
> >> > lot of
> >> > challenges to efficiently use SSD for swap:
> >>
> >> Many of below item could be applied in in-memory swap like zram, zcache.
> >>
> >> >
> >> > 1. Lock contentions (swap_lock, anon_vma mutex, swap address space
> >> > lock)
> >> > 2. TLB flush overhead. To reclaim one page, we need at least 2 TLB
> >> > flush. This
> >> > overhead is very high even in a normal 2-socket machine.
> >> > 3. Better swap IO pattern. Both direct and kswapd page reclaim can do
> >> > swap,
> >> > which makes swap IO pattern is interleave. Block layer isn't always
> >> > efficient
> >> > to do request merge. Such IO pattern also makes swap prefetch hard.
> >>
> >> Agreed.
> >>
> >> > 4. Swap map scan overhead. Swap in-memory map scan scans an array, which
> >> > is
> >> > very inefficient, especially if swap storage is fast.
> >>
> >> Agreed.
> >>
>
> 5. SSD related optimization, mainly discard support.
>
> Now swap codes are based on each swap slots. it means it can't
> optimize discard feature since getting meaningful performance gain, it
> requires 2 pages at least. Of course it's based on eMMC. In case of
> SSD. it requires more pages to support discard.
>
> To address issue. I consider the batched discard approach used at filesystem.
> *Sometime* scan all empty slot and it issues discard continuous swap
> slots as many as possible.
I posted a patch to make discard async before, which is almost good to me, though we
still discard a cluster.
http://marc.info/?l=linux-mm&m=135087309208120&w=2
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next prev parent reply other threads:[~2013-01-27 14:19 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-22 6:53 Shaohua Li
2013-01-23 7:58 ` Minchan Kim
2013-01-23 19:04 ` Seth Jennings
2013-01-24 1:40 ` Minchan Kim
2013-01-24 8:29 ` Simon Jeons
2013-01-24 2:02 ` Shaohua Li
2013-01-24 7:52 ` Simon Jeons
2013-01-24 9:09 ` Simon Jeons
2013-01-26 4:40 ` Kyungmin Park
2013-01-27 0:26 ` Simon Jeons
2013-01-27 14:18 ` Shaohua Li [this message]
2013-01-28 7:37 ` Kyungmin Park
2013-02-01 12:37 ` Kyungmin Park
2013-02-04 4:56 ` Hugh Dickins
2013-02-19 6:15 ` Shaohua Li
2013-02-19 19:41 ` Hugh Dickins
2013-04-05 0:17 ` Simon Jeons
2013-04-05 8:08 ` Minchan Kim
2013-01-23 16:56 ` Seth Jennings
2013-01-24 6:28 ` Simon Jeons
2013-03-15 9:39 ` Simon Jeons
2013-03-18 10:38 ` Bob Liu
2013-03-19 1:27 ` Shaohua Li
2013-03-19 1:32 ` Simon Jeons
2013-03-19 5:57 ` Shaohua Li
2013-03-19 6:10 ` Simon Jeons
2013-03-19 4:25 ` Wanpeng Li
2013-03-19 4:25 ` Wanpeng Li
2013-04-28 8:12 ` Simon Jeons
[not found] <766b9855-adf5-47ce-9484-971f88ff0e54@default>
2013-01-23 23:05 ` Dan Magenheimer
2013-01-24 2:11 ` Shaohua Li
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