From: Yosry Ahmed <yosryahmed@google.com>
To: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>,
lsf-pc@lists.linux-foundation.org,
Johannes Weiner <hannes@cmpxchg.org>,
Linux-MM <linux-mm@kvack.org>, Michal Hocko <mhocko@kernel.org>,
Shakeel Butt <shakeelb@google.com>,
David Rientjes <rientjes@google.com>,
Hugh Dickins <hughd@google.com>,
Seth Jennings <sjenning@redhat.com>,
Dan Streetman <ddstreet@ieee.org>,
Vitaly Wool <vitaly.wool@konsulko.com>,
Yang Shi <shy828301@gmail.com>, Peter Xu <peterx@redhat.com>,
Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>,
Michal Hocko <mhocko@suse.com>, Wei Xu <weixugc@google.com>
Subject: Re: [LSF/MM/BPF TOPIC] Swap Abstraction / Native Zswap
Date: Tue, 28 Mar 2023 14:01:09 -0700 [thread overview]
Message-ID: <CAJD7tkaGDBxO2q3X5oQj+C11z3mHdFK_Dw0anFPWjWPp99ra7g@mail.gmail.com> (raw)
In-Reply-To: <ZCNTEAWjJRUWapAW@google.com>
On Tue, Mar 28, 2023 at 1:50 PM Chris Li <chrisl@kernel.org> wrote:
>
> On Tue, Mar 28, 2023 at 12:59:31AM -0700, Yosry Ahmed wrote:
> > > > I don't have a problem with this approach, it is not really clean as
> > > > we still treat zswap as a swapfile and have to deal with a lot of
> > > > unnecessary code like swap slots handling and whatnot.
> > >
> > > These are existing code?
>
> Yes. The ghost swap file are existing code used in Google for many years.
>
> > I was referring to the fact that today with zswap being tied to
> > swapfiles we do some necessary work such as searching for swap slots
> > during swapout. The initial swap_desc approach aimed to avoid that.
> > With this minimal ghost swapfile approach we retain this unfavorable
> > behavior.
>
> Can you explain how you can avoid the free swap entry search
> in the swap descriptor world?
For zswap, in the swap descriptor world, you just need to allocate a
struct zswap_entry and have the swap descriptor point to it. No need
for swap slot management since we are not tied to a swapfile and pages
in zswap do not have a specific position.
>
> The swap entry space is smaller than the memory address space and
> there are other swapfiles can use the swap entry. You do need to do
> some swap entry space management work to get a free entry. That to
> me seems unavoidable, am I missing something?
>
> > > Personally, I have no problem to change the design of swap code to add
> > > useful features. Just want to check whether we can do that step by step
> > > and show benefit and cost clearly in each step.
> >
> > Right. I understand and totally agree, even from a development point
> > of view it's much better to make big changes incrementally to avoid
> > doing a lot of work that ends up going nowhere. I am just trying to
> > make sure that whatever we decide is indeed a step in the right
> > direction.
>
> The ghost swap file patch already exists. We might just share it here
> for the discussion purpose, list the pros and cons.
The ghost swap file patch that we have does not work upstream because:
(a) It involves ABI changes (we start supporting swapon on a sparse
0-block-length file). Hence, it cannot be an incremental/intermediate
step because once we start supporting it we cannot take it back.
(b) It requires modifications to the swapon utility to work.
In my response to Johannes [1] I described an alternative that can
work upstream and wouldn't have ABI changes or need changes to swapon.
[1]https://lore.kernel.org/linux-mm/CAJD7tkbudmPTEumgKJZ5pXy6O79ySbGiCnAZXnUUuEmfZ6KCtQ@mail.gmail.com/
>
> Chris
>
next prev parent reply other threads:[~2023-03-28 21:01 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-18 22:38 [LSF/MM/BPF TOPIC] Swap Abstraction / Native Zswap Yosry Ahmed
2023-02-19 4:31 ` Matthew Wilcox
2023-02-19 9:34 ` Yosry Ahmed
2023-02-28 23:22 ` Chris Li
2023-03-01 0:08 ` Matthew Wilcox
2023-03-01 23:22 ` Chris Li
2023-02-21 18:39 ` Yang Shi
2023-02-21 18:56 ` Yosry Ahmed
2023-02-21 19:26 ` Yang Shi
2023-02-21 19:46 ` Yosry Ahmed
2023-02-21 23:34 ` Yang Shi
2023-02-21 23:38 ` Yosry Ahmed
2023-02-22 16:57 ` Johannes Weiner
2023-02-22 22:46 ` Yosry Ahmed
2023-02-28 4:29 ` Kalesh Singh
2023-02-28 8:09 ` Yosry Ahmed
2023-02-28 4:54 ` Sergey Senozhatsky
2023-02-28 8:12 ` Yosry Ahmed
2023-02-28 23:29 ` Minchan Kim
2023-03-02 0:58 ` Yosry Ahmed
2023-03-02 1:25 ` Yosry Ahmed
2023-03-02 17:05 ` Chris Li
2023-03-02 17:47 ` Chris Li
2023-03-02 18:15 ` Johannes Weiner
2023-03-02 18:56 ` Chris Li
2023-03-02 18:23 ` Rik van Riel
2023-03-02 21:42 ` Chris Li
2023-03-02 22:36 ` Rik van Riel
2023-03-02 22:55 ` Yosry Ahmed
2023-03-03 4:05 ` Chris Li
2023-03-03 0:01 ` Chris Li
2023-03-02 16:58 ` Chris Li
2023-03-01 10:44 ` Sergey Senozhatsky
2023-03-02 1:01 ` Yosry Ahmed
2023-02-28 23:11 ` Chris Li
2023-03-02 0:30 ` Yosry Ahmed
2023-03-02 1:00 ` Yosry Ahmed
2023-03-02 16:51 ` Chris Li
2023-03-03 0:33 ` Minchan Kim
2023-03-03 0:49 ` Yosry Ahmed
2023-03-03 1:25 ` Minchan Kim
2023-03-03 17:15 ` Yosry Ahmed
2023-03-09 12:48 ` Huang, Ying
2023-03-09 19:58 ` Chris Li
2023-03-09 20:19 ` Yosry Ahmed
2023-03-10 3:06 ` Huang, Ying
2023-03-10 23:14 ` Chris Li
2023-03-13 1:10 ` Huang, Ying
2023-03-15 7:41 ` Yosry Ahmed
2023-03-16 1:42 ` Huang, Ying
2023-03-11 1:06 ` Yosry Ahmed
2023-03-13 2:12 ` Huang, Ying
2023-03-15 8:01 ` Yosry Ahmed
2023-03-16 7:50 ` Huang, Ying
2023-03-17 10:19 ` Yosry Ahmed
2023-03-17 18:19 ` Chris Li
2023-03-17 18:23 ` Yosry Ahmed
2023-03-20 2:55 ` Huang, Ying
2023-03-20 6:25 ` Chris Li
2023-03-23 0:56 ` Huang, Ying
2023-03-23 6:46 ` Chris Li
2023-03-23 6:56 ` Huang, Ying
2023-03-23 18:28 ` Chris Li
2023-03-23 18:40 ` Yosry Ahmed
2023-03-23 19:49 ` Chris Li
2023-03-23 19:54 ` Yosry Ahmed
2023-03-23 21:10 ` Chris Li
2023-03-24 17:28 ` Chris Li
2023-03-22 5:56 ` Yosry Ahmed
2023-03-23 1:48 ` Huang, Ying
2023-03-23 2:21 ` Yosry Ahmed
2023-03-23 3:16 ` Huang, Ying
2023-03-23 3:27 ` Yosry Ahmed
2023-03-23 5:37 ` Huang, Ying
2023-03-23 15:18 ` Yosry Ahmed
2023-03-24 2:37 ` Huang, Ying
2023-03-24 7:28 ` Yosry Ahmed
2023-03-24 17:23 ` Chris Li
2023-03-27 1:23 ` Huang, Ying
2023-03-28 5:54 ` Yosry Ahmed
2023-03-28 6:20 ` Huang, Ying
2023-03-28 6:29 ` Yosry Ahmed
2023-03-28 6:59 ` Huang, Ying
2023-03-28 7:59 ` Yosry Ahmed
2023-03-28 14:14 ` Johannes Weiner
2023-03-28 19:59 ` Yosry Ahmed
2023-03-28 21:22 ` Chris Li
2023-03-28 21:30 ` Yosry Ahmed
2023-03-28 20:50 ` Chris Li
2023-03-28 21:01 ` Yosry Ahmed [this message]
2023-03-28 21:32 ` Chris Li
2023-03-28 21:44 ` Yosry Ahmed
2023-03-28 22:01 ` Chris Li
2023-03-28 22:02 ` Yosry Ahmed
2023-03-29 1:31 ` Huang, Ying
2023-03-29 1:41 ` Yosry Ahmed
2023-03-29 16:04 ` Chris Li
2023-04-04 8:24 ` Huang, Ying
2023-04-04 8:10 ` Huang, Ying
2023-04-04 8:47 ` Yosry Ahmed
2023-04-06 1:40 ` Huang, Ying
2023-03-29 15:22 ` Chris Li
2023-03-10 2:07 ` Luis Chamberlain
2023-03-10 2:15 ` Yosry Ahmed
2023-05-12 3:07 ` Yosry Ahmed
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