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Mon, 25 Mar 2024 14:29:52 -0700 (PDT) MIME-Version: 1.0 References: <20240320-zswap-xarray-v8-1-dc08ee9f8744@kernel.org> <20240325133546.ffd728d1c309ba58eadb179c@linux-foundation.org> In-Reply-To: <20240325133546.ffd728d1c309ba58eadb179c@linux-foundation.org> From: Chris Li Date: Mon, 25 Mar 2024 14:29:41 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v8] zswap: replace RB tree with xarray To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Yosry Ahmed , Nhat Pham , Johannes Weiner , Chengming Zhou , Barry Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 98C86C000A X-Stat-Signature: agsms7jukfbgyyrfi1rkpo4bra58nwsa X-HE-Tag: 1711402195-463780 X-HE-Meta: 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 RcCXWQB3 tTcj9MasF2axaf45M4jR9a3tCRh1qojAk2eE5NvXmf8Se5aLOMXE3KzhbGPUvPsuGlXqAmEhPaYfUffjoi16q9WFWQXoeraU14qTULouMXO8a1coBmb0JTp4i4+IVA3NCG0oJTph0GHVRCj3PHG9r97j1yYyatAm8Q4IDAn0mb1BA9OfDAlxR7n+b4DX7IDQbyVd/f3x/rPuU6u5vn+pp4RF5LYjBUj9f6RS1ztJcMo9TrueBNE0Zm4wPub9Lq1C/4XuFx6rAV9mKN59A4V7lEEMu3d0AW29IYkglWlZIiB3FS/8GI6otJfhqtgtv6OtBBt6roNMVvkn5ynXVgIN0fFYqvg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 25, 2024 at 1:35=E2=80=AFPM Andrew Morton wrote: > > On Wed, 20 Mar 2024 12:31:38 -0700 Chris Li wrote: > > > Very deep RB tree requires rebalance at times. That > > contributes to the zswap fault latencies. Xarray does not > > need to perform tree rebalance. Replacing RB tree to xarray > > can have some small performance gain. > > > > One small difference is that xarray insert might fail with > > ENOMEM, while RB tree insert does not allocate additional > > memory. > > > > The zswap_entry size will reduce a bit due to removing the > > RB node, which has two pointers and a color field. Xarray > > store the pointer in the xarray tree rather than the > > zswap_entry. Every entry has one pointer from the xarray > > tree. Overall, switching to xarray should save some memory, > > if the swap entries are densely packed. > > > > Notice the zswap_rb_search and zswap_rb_insert always > > followed by zswap_rb_erase. Use xa_erase and xa_store > > directly. That saves one tree lookup as well. > > > > Remove zswap_invalidate_entry due to no need to call > > zswap_rb_erase any more. Use zswap_free_entry instead. > > > > The "struct zswap_tree" has been replaced by "struct xarray". > > The tree spin lock has transferred to the xarray lock. > > > > Run the kernel build testing 10 times for each version, averages: > > (memory.max=3D2GB, zswap shrinker and writeback enabled, > > one 50GB swapfile, 24 HT core, 32 jobs) > > > > So this conflits with Johannes's "mm: zswap: fix data loss on > SWP_SYNCHRONOUS_IO devices", right in the critical part of > zswap_load(). Naive resolution of that conflict would have resulted in > basically reverting Johannes's fix. > > That fix is cc:stable so we do want it to have a clean run in > linux-next before sending it upstream. So I'll drop this patch > ("zswap: replace RB tree with xarray") for now. Please redo it against > latest mm-unstable and of course, be sure to preserve Johannes's fix, > thanks. Sure, I will wait for your mm-unstable update that contains Jonanne's fix then re-submit a new version. Chris