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b=TJpmCq71lf4vNsjlzVfawi9feXaYdWGIp2Tx/oFwULPbEo//ZIlensVPiLKZYUMaz 59QZukL5NOjLSUFTY4rB3KSpTvLIWFGNHSg8b7rIHF4PRKfmJpZr4UcahgmwpB5IQp lXGOX9VUmEmQdUIV+AqeoDTXj50gf9NdIQ9XnxhE= Date: Mon, 25 Mar 2024 13:35:46 -0700 From: Andrew Morton To: Chris Li Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Yosry Ahmed , Nhat Pham , Johannes Weiner , "Matthew Wilcox (Oracle)" , Chengming Zhou , Barry Song , Johannes Weiner Subject: Re: [PATCH v8] zswap: replace RB tree with xarray Message-Id: <20240325133546.ffd728d1c309ba58eadb179c@linux-foundation.org> In-Reply-To: <20240320-zswap-xarray-v8-1-dc08ee9f8744@kernel.org> References: <20240320-zswap-xarray-v8-1-dc08ee9f8744@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6FF61A001A X-Rspam-User: X-Stat-Signature: zjgr9azk5ueah6zctew1e141nr9tgk6f X-Rspamd-Server: rspam03 X-HE-Tag: 1711398948-55759 X-HE-Meta: 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 RAUIokua MZi64UeGycqp4M6lchUUosudDK0I1Ss5s7OhKaiANVhsgG3m3c3mrD6PeF7yIUO+voUvZFwHKZ5GQuHaqT7wzWDSjz/aBUyoQAcd222F70aoltmzO/UvAO9CIYrSlWZERSbHaC5ELomDvDjsNk9bSE050uDldNlmwZDOL9/Dqpv9qesvSB8pXNgMY2gu6Hyj+3Ymd4Pn6XdUyAUw/rcP0Ile4+/2bCMEYPWl5MRSQupDmiDHMXaZEe1fYadcgliDFx+M5bhjrovARrOg2dRt74QYe6TCd4jiUqTZW 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 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=2GB, 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.