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b=WAYnUTXMTXFJKySbFuqmzPeYKgqYlqqRd7oCs3fqws60PvxNF/9klFq7Oc0tur97v v2klAFQ0UtKjB23cHitm4X8qmLcY0tql6Sfay8DLht6bG41WBKFxrtPijuj5XzIKyW /RENMf0MhvCZ9/bNd/7Hx1ljqhzWXqJnaUN1Whoi1WK1/tJWt9JF4rWiswaTBi48Dg EbzImNa1nN+ucQhgWHRlTi0W0x8A6k1dQsXIM67gUPzMXzz75Yg0TfwpDSAqw87viy WUf82vC80QtmXOSQSNGU+hi75dVP8dHJ6WHuEq5Ix6PFeyY0nQ9kBSmTehgred27gu znOwWLZdQ1T7Q== Date: Mon, 28 Sep 2026 09:19:37 -1000 Message-ID: From: Tejun Heo To: Liz Fong-Jones Cc: Christian Brauner , Jan Kara , Alexander Viro , Jens Axboe , Andrew Morton , Johannes Weiner , Roman Gushchin , Shakeel Butt , Xin Yin , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, ian@honeycomb.io, stable@vger.kernel.org Subject: Re: [PATCH] writeback: let foreign flushes reach dying cgwbs In-Reply-To: <20260926-wb-dying-cgwb-flush-v1-1-a8d898085a3a@honeycomb.io> References: <20260926-wb-dying-cgwb-flush-v1-1-a8d898085a3a@honeycomb.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3D3781C0008 X-Stat-Signature: g56wmghoc3o563jnw7og6o739dke8pf7 X-HE-Tag: 1790623179-439125 X-HE-Meta: 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 Al3+Gbgh x2k1LwzjLd+IfU8CeY5JvShpWtGyd/w5l7QK73PI/yZfQRJbOq7k/eq6F0loYwdEbM252cwtEhmi4/61xKBKmeXEE54W3SOWnfSbrWHuSMA7tfiEKGzEOcjJ1Htu++sKOYT9N8rrVeSNn7IwcuD0Ge6DVVxFAnOI1Qm/8L9IxH2otKlAGyRUUseLkzvzkJjkFyP7l6wEmqFlnIzojTgDCEFcLB0VHgiut17gf3n8v5NDfoQGe/rB+IMZm1oqpGC9CLa7SZ6gCjY8Xpyp0/yM/H5V0nQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, Liz. On Sun, Sep 27, 2026 at 05:04:39AM +0000, Liz Fong-Jones wrote: > Fall back to searching bdi->wb_list, where killed wbs stay until they > are released. With commit 168a8c13159c ("writeback: size foreign > flushes by target wb dirty pages"), the flush is then sized from the > wb's own dirty pages and writes out what the replacement dirtied. Instead of walking bdi->wb_list, can't we update the lifetime rule so that a wb stays on bdi->cgwb_tree until it's actually released? That is, remove it from the tree in cgwb_release_workfn() instead of cgwb_kill() and have the creation paths skip dying wbs. cgroup_writeback_by_id() would then find the dying wb through the regular lookup. Note that the blkcg association check in wb_get_lookup() would have to move to the creation side. If io is enabled on the removed cgroup, cgroup_get_e_css() returns an ancestor's io css and a dying wb would never match. > Fixes: d62241c7a406 ("writeback, memcg: Implement cgroup_writeback_by_id()") > Cc: stable@vger.kernel.org I don't think this qualifies as a fix. Can you drop the Fixes: and stable tags? Thanks. -- tejun