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b=EBHsSDNp7SJRGlgzs1s4PvOgtoI+WThEUd6L3zusu14fF9Utndhrof2SlWJ0i39Pe 9T26TGOv85czWPVV7eDQXIPcm+GnstsRvy7bnniBlBr06sjbs5zVXiUfbAJKt7wFUS IHKxtSWvSyFeWy8eHkFsK0IlLb0Gqvi+Q/IiYy+/gxptoTtALdupBaU0TWhdtgEtOo 8jKr/9WKYjKSH3LgPyhy9N7QeycHORIo0YPIWrXdGLHd6ay0+BofOOWNVw9iIp23re X2F1VUs7t7NeY2p3NQsglPI4wW7nGfL2vE4+9mVc7+PQ1RXIjh0q2jnKhtz/utdKvB 4mNxoaGwLxrLA== Date: Fri, 02 Oct 2026 09:21:11 -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 Subject: Re: [PATCH v5 2/3] writeback: let foreign flushes reach dying cgwbs In-Reply-To: <20261001-wb-dying-cgwb-flush-v5-2-8361eb8c65c6@honeycomb.io> References: <20261001-wb-dying-cgwb-flush-v5-0-8361eb8c65c6@honeycomb.io> <20261001-wb-dying-cgwb-flush-v5-2-8361eb8c65c6@honeycomb.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B4ECE40004 X-Rspam-User: X-Stat-Signature: ghubshwndptqfpstixainjpgysse36kg X-HE-Tag: 1790968872-315693 X-HE-Meta: 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 nOuxEKiK A1AZlN2K0G/WOhts3ovbmDE3KM8g9NyImQ2LvTZlpGkeCbPfc1gNavxT99KHJZa/4uvbzpyNF0DjqMym1Tr61BIi222l34LBTgN1IS6j63Wpb5lEM5RDRKe71YpiTRk+dmwJvcNgFLREEuoFz7ERlDWMKwDWF6hwHhfM5uj6r/0CwMQwPzlMH5OppnL/eNPK2quCB7ZyO7tOjNaGcsM2vgy856ATrJoTlSHeYZTbmHEPv4W4Tmyq3CdMhBePbkTiZVdPlnnqSqDgfcrRFh2+0AZxIuQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, Liz. On Thu, Oct 01, 2026 at 11:50:20PM +0000, Liz Fong-Jones wrote: > + * The wb may have been killed and its blkcg association may be stale. This > + * is what foreign flushes want: they target the wb that owns the dirty > + * inodes, which can be a killed one. Use wb_get_create() to get a wb to > + * attach inodes to. The next patch attaches inodes to what this returns. Maybe just say that it returns the wb in @memcg_css's slot, killed or not? > + * This function uses css_get() on @memcg_css and thus expects its refcnt > + * to be positive on invocation. IOW, rcu_read_lock() protection on > + * @memcg_css isn't enough. try_get it before calling this function. This describes cgwb_create(), so wb_get_create() is where it belongs. The struct bdi_writeback comment in backing-dev-defs.h and wb_dying()'s still describe the old lifetime rule. Can you update them too? Acked-by: Tejun Heo Thanks. -- tejun