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Tue, 04 Aug 2026 18:27:06 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:32eb:b46b:e9eb:65c5]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3903f5e21c7sm460514a91.3.2026.08.04.18.27.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Aug 2026 18:27:05 -0700 (PDT) Date: Wed, 5 Aug 2026 10:27:01 +0900 From: Sergey Senozhatsky To: "Barry Song (Xiaomi)" Cc: senozhatsky@chromium.org, akpm@linux-foundation.org, bigeasy@linutronix.de, hdanton@sina.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, ryncsn@gmail.com, yosry.ahmed@linux.dev, surenb@google.com, Dongdong Zhang Subject: Re: [RFC PATCH] zram: avoid preemption with CPU-based compression backends Message-ID: References: <20260805005545.66112-1-baohua@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260805005545.66112-1-baohua@kernel.org> On (26/08/05 08:55), Barry Song (Xiaomi) wrote: > Since commit 2efa9e9eb4db ("zram: permit preemption with active > compression stream"), a major Android regression has been reported. > > The reason is that compression/decompression is now sleepable and > preemptible. This means a stream may be migrated to another CPU or > be preempted while holding the stream mutex. As a result, high > priority UI threads may get stuck waiting for the mutex during swap-in. [..] > We add an async flag (currently false for almost all backends) to > indicate whether a backend is asynchronous. For synchronous > backends, we use preempt_disable() in the !PREEMPT_RT case. A I wonder what does that report say. Is that what I think it is (we discussed something RT related privately recently)?