From: Nhat Pham <nphamcs@gmail.com>
To: Askar Safin <safinaskar@gmail.com>
Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org,
apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org,
baolin.wang@linux.alibaba.com, bhe@redhat.com, byungchul@sk.com,
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matthew.brost@intel.com, mhocko@suse.com, muchun.song@linux.dev,
npache@redhat.com, pavel@kernel.org, peterx@redhat.com,
peterz@infradead.org, pfalcato@suse.de, rafael@kernel.org,
rakie.kim@sk.com, riel@surriel.com, roman.gushchin@linux.dev,
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shikemeng@huaweicloud.com, surenb@google.com, tglx@kernel.org,
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ying.huang@linux.alibaba.com, yosry.ahmed@linux.dev,
yuanchu@google.com, zhengqi.arch@bytedance.com, ziy@nvidia.com,
Kairui Song <ryncsn@gmail.com>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v5 00/21] Virtual Swap Space
Date: Tue, 24 Mar 2026 13:23:22 -0400 [thread overview]
Message-ID: <CAKEwX=MgoPmiFdBQXK_4=XuR-8mVpGr+3Ku2MfjPmHCeuUdGJg@mail.gmail.com> (raw)
In-Reply-To: <20260324131931.4004123-1-safinaskar@gmail.com>
On Tue, Mar 24, 2026 at 9:19 AM Askar Safin <safinaskar@gmail.com> wrote:
>
> Nhat Pham <nphamcs@gmail.com>:
> > We can even perform compressed writeback
> > (i.e writing these pages without decompressing them) (see [12]).
>
> > [12]: https://lore.kernel.org/linux-mm/ZeZSDLWwDed0CgT3@casper.infradead.org/
>
> This is supported in zram. The support was added here:
> https://lore.kernel.org/all/20251201094754.4149975-1-senozhatsky@chromium.org/ .
> It is already in mainline.
I'm aware of that work. It's an improvement, but my understanding is:
1. It only works for zram.
2. We still occupy the full PAGE_SIZE slot.
3. The writeback IO request is still of size PAGE_SIZE.
So we're saving the CPU work for decompression, but not the rest of
the potential benefits of compressed writeback.
For zswap, decoupling zswap and disk swap is a pre-requisite
(otherwise every zswap slot occupy a PAGE_SIZE slot in the swapfile
anyway).
Then, we have two alternatives. Either we implement a small-slot
allocator for swapfile-infra, or we writeback a full backing page for
compressed memory. The second option is a bit more straightforward,
but then we lose relative age of these objects - a backing page might
combine very recent compressed pages and very old compressed pages.
These approaches have different performance tradeoffs and need to be
evaluated. But anyway this is future work.
next prev parent reply other threads:[~2026-03-24 17:23 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-20 19:27 Nhat Pham
2026-03-20 19:27 ` [PATCH v5 01/21] mm/swap: decouple swap cache from physical swap infrastructure Nhat Pham
2026-03-20 19:27 ` [PATCH v5 02/21] swap: rearrange the swap header file Nhat Pham
2026-03-20 19:27 ` [PATCH v5 03/21] mm: swap: add an abstract API for locking out swapoff Nhat Pham
2026-03-20 19:27 ` [PATCH v5 04/21] zswap: add new helpers for zswap entry operations Nhat Pham
2026-03-20 19:27 ` [PATCH v5 05/21] mm/swap: add a new function to check if a swap entry is in swap cached Nhat Pham
2026-03-20 19:27 ` [PATCH v5 06/21] mm: swap: add a separate type for physical swap slots Nhat Pham
2026-03-20 19:27 ` [PATCH v5 07/21] mm: create scaffolds for the new virtual swap implementation Nhat Pham
2026-03-20 19:27 ` [PATCH v5 08/21] zswap: prepare zswap for swap virtualization Nhat Pham
2026-03-20 19:27 ` [PATCH v5 09/21] mm: swap: allocate a virtual swap slot for each swapped out page Nhat Pham
2026-03-20 19:27 ` [PATCH v5 10/21] swap: move swap cache to virtual swap descriptor Nhat Pham
2026-03-20 19:27 ` [PATCH v5 11/21] zswap: move zswap entry management to the " Nhat Pham
2026-03-20 19:27 ` [PATCH v5 12/21] swap: implement the swap_cgroup API using virtual swap Nhat Pham
2026-03-20 19:27 ` [PATCH v5 13/21] swap: manage swap entry lifecycle at the virtual swap layer Nhat Pham
2026-03-20 19:27 ` [PATCH v5 14/21] mm: swap: decouple virtual swap slot from backing store Nhat Pham
2026-03-20 19:27 ` [PATCH v5 15/21] zswap: do not start zswap shrinker if there is no physical swap slots Nhat Pham
2026-03-20 19:27 ` [PATCH v5 16/21] swap: do not unnecesarily pin readahead swap entries Nhat Pham
2026-03-20 19:27 ` [PATCH v5 17/21] swapfile: remove zeromap bitmap Nhat Pham
2026-03-20 19:27 ` [PATCH v5 18/21] memcg: swap: only charge physical swap slots Nhat Pham
2026-03-20 19:27 ` [PATCH v5 19/21] swap: simplify swapoff using virtual swap Nhat Pham
2026-03-20 19:27 ` [PATCH v5 20/21] swapfile: replace the swap map with bitmaps Nhat Pham
2026-03-20 19:27 ` [PATCH v5 21/21] vswap: batch contiguous vswap free calls Nhat Pham
2026-03-21 18:22 ` [PATCH v5 00/21] Virtual Swap Space Andrew Morton
2026-03-22 2:18 ` Roman Gushchin
[not found] ` <CAMgjq7AiUr_Ntj51qoqvV+=XbEATjr7S4MH+rgD32T5pHfF7mg@mail.gmail.com>
2026-03-23 15:32 ` Nhat Pham
2026-03-23 16:40 ` Kairui Song
2026-03-23 20:05 ` Nhat Pham
2026-03-25 18:53 ` YoungJun Park
2026-03-24 13:19 ` Askar Safin
2026-03-24 17:23 ` Nhat Pham [this message]
2026-03-25 2:35 ` Askar Safin
2026-03-25 18:36 ` YoungJun Park
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