From: "Huang, Ying" <ying.huang@intel.com>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Chris Li <chrisl@kernel.org>,
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: Thu, 16 Mar 2023 09:42:48 +0800 [thread overview]
Message-ID: <87fsa55v53.fsf@yhuang6-desk2.ccr.corp.intel.com> (raw)
In-Reply-To: <CAJD7tkb4zK+ZzrQqgdTHE1r-Br9DKEER-gW3DFfJ+Sh9Rgs6+g@mail.gmail.com> (Yosry Ahmed's message of "Wed, 15 Mar 2023 00:41:45 -0700")
Yosry Ahmed <yosryahmed@google.com> writes:
> On Sun, Mar 12, 2023 at 6:11 PM Huang, Ying <ying.huang@intel.com> wrote:
>>
>> Chris Li <chrisl@kernel.org> writes:
>>
>> > On Fri, Mar 10, 2023 at 11:06:37AM +0800, Huang, Ying wrote:
>> >> > Unfortunately it's a little bit more. 24 is the extra overhead.
>> >> >
>> >> > Today we have an xarray entry for each swapped out page, that either
>> >> > has the swapcache pointer or the shadow entry.
>> >> >
>> >> > With this implementation, we have an xarray entry for each swapped out
>> >> > page, that has a pointer to the swap_desc.
>> >> >
>> >> > Ignoring the overhead of the xarray itself, we have (8 + 24) / (8 + 1) = 3.5556.
>> >>
>> >> OK. I see. We can only hold 8 bytes for each xarray entry. To save
>> >> memory usage, we can allocate multiple swap_desc (e.g., 16) for each
>> >> xarray entry. Then the memory usage of xarray becomes 1/N.
>> >
>> > The xarray look up key is the swap offset from the swap entry. If you
>> > put more than one swap_desc under the one xarray entry. It will mean
>> > all those different swap_descs will share a swap offset.
>>
>> For example, if we allocate 16 swap_desc for each xarray entry. Then,
>> we can use (swap_desc_index >> 4) as key to lookup xarray, and
>> (swap_desc_index & 0x15) to index inside 16 swap_desc for the xarray
>> entry.
>
> With this approach we save (16 - 1) * 8 = 120 bytes per 16 swap_descs,
> but only if we use the space for 16 swap_desc's fully. As pages are
> swapped in, we can easily end up with less than 16 swap_descs for one
> xarray entry, how do we deal with such fragmentation?
>
> At 11 swap_descs per xarray entry, we are not saving any memory
> (wasting 24 * 5 = 120 bytes). Below 11 swap_descs, we are wasting more
> memory than we are saving.
Yes. This approach isn't very fragmentation friendly. xarray isn't
too. So, I think we should try to reduce fragmentation anyway, for
example, reuse freed swap_desc IDs ASAP, or allocate less swap_desc per
xarray entry (e.g., 4), etc.
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2023-03-16 1:44 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 [this message]
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
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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